Cell as a biological system (multiple choice). Do all living organisms have a cell structure? Biology: the cellular structure of the body The cellular structure of all living organisms

Theory for task 4 from the exam in biology

Cell as a biological system

Modern cellular theory, its main provisions, the role in the formation of the modern natural-science picture of the world. Development of knowledge about the cell. The cellular structure of organisms is the basis of the unity of the organic world, proof of the relationship of living nature

Modern cellular theory, its main provisions, role in the formation of the modern natural-science picture of the world

One of the fundamental concepts in modern biology is the idea that all living organisms have a cellular structure. Science deals with the study of the structure of the cell, its vital activity and interaction with the environment. cytology now commonly referred to as cell biology. Cytology owes its appearance to the formulation cell theory(1838-1839, M. Schleiden, T. Schwann, supplemented in 1855 by R. Virchow).

cell theory is a generalized idea of ​​the structure and functions of cells as living units, their reproduction and role in the formation of multicellular organisms.

The main provisions of the cell theory:

1. A cell is a unit of structure, life activity, growth and development of living organisms - there is no life outside the cell.
2. Cell - one system, consisting of a set of elements naturally connected with each other, representing a certain holistic formation.
3. The cells of all organisms are similar in their own way. chemical composition, structure and function.
4. New cells are formed only as a result of division of mother cells (“cell from cell”).
5. The cells of multicellular organisms form tissues, and organs are made up of tissues. The life of an organism as a whole is determined by the interaction of its constituent cells.
6. The cells of multicellular organisms have a complete set of genes, but differ from each other in that different groups of genes work for them, which results in the morphological and functional diversity of cells - differentiation.

Thanks to the creation of the cellular theory, it became clear that the cell is the smallest unit of life, an elementary living system, which has all the signs and properties of living things. The formulation of the cellular theory became the most important prerequisite for the development of views on heredity and variability, since the identification of their nature and their inherent laws inevitably suggested the universality of the structure of living organisms. Revealing the unity of the chemical composition and structural plan of cells served as an impetus for the development of ideas about the origin of living organisms and their evolution. In addition, the origin of multicellular organisms from a single cell in the process embryonic development has become the dogma of modern embryology.

Development of knowledge about the cell

Until the 17th century, man knew nothing at all about the microstructure of the objects surrounding him and perceived the world with the naked eye. The instrument for studying the microworld, the microscope, was invented approximately in 1590 by the Dutch mechanics G. and Z. Jansen, but its imperfection made it impossible to examine sufficiently small objects. Only the creation on its basis of the so-called compound microscope by K. Drebbel (1572-1634) contributed to the progress in this area.

In 1665, the English physicist R. Hooke (1635-1703) improved the design of the microscope and the technology of grinding lenses, and, wanting to make sure that the image quality improved, he examined cork sections under it, charcoal and living plants. On the sections, he found the smallest pores resembling a honeycomb, and called them cells (from lat. cellula cell, cell). It is interesting to note that R. Hooke considered the cell membrane to be the main component of the cell.

In the second half of the 17th century, the works of the most prominent microscopists M. Malpighi (1628-1694) and N. Gru (1641-1712) appeared, who also discovered the cellular structure of many plants.

To make sure that what R. Hooke and other scientists saw was true, the Dutch merchant A. van Leeuwenhoek, who did not have a special education, independently developed a microscope design that was fundamentally different from the existing one, and improved the lens manufacturing technology. This allowed him to achieve an increase of 275-300 times and to consider such details of the structure that were technically inaccessible to other scientists. A. van Leeuwenhoek was an unsurpassed observer: he carefully sketched and described what he saw under a microscope, but did not seek to explain it. He discovered unicellular organisms, including bacteria, found nuclei, chloroplasts, thickenings of cell walls in plant cells, but his discoveries could be evaluated much later.

Discoveries of the components of the internal structure of organisms in the first half of the 19th century followed one after another. G. Mol distinguished in plant cells living matter and a watery liquid - cell sap, discovered pores. The English botanist R. Brown (1773-1858) discovered the nucleus in orchid cells in 1831, then it was found in all plant cells. The Czech scientist J. Purkinje (1787-1869) introduced the term "protoplasm" (1840) to refer to the semi-liquid gelatinous contents of a cell without a nucleus. The Belgian botanist M. Schleiden (1804-1881) advanced further than all his contemporaries, who, studying the development and differentiation of various cell structures higher plants, proved that all plant organisms originate from a single cell. He also considered rounded nucleolus bodies in the nuclei of onion scale cells (1842).

In 1827, the Russian embryologist K. Baer discovered the eggs of humans and other mammals, thereby refuting the notion of the development of an organism exclusively from male gametes. In addition, he proved the formation of a multicellular animal organism from a single cell - a fertilized egg, as well as the similarity of the stages of embryonic development of multicellular animals, which suggested the unity of their origin. The information accumulated by the middle of the 19th century required generalization, which became the cellular theory. Biology owes its formulation to the German zoologist T. Schwann (1810-1882), who, based on his own data and M. Schleiden's conclusions on the development of plants, suggested that if a nucleus is present in any formation visible under a microscope, then this formation is cell. Based on this criterion, T. Schwann formulated the main provisions of the cell theory.

The German physician and pathologist R. Virchow (1821-1902) introduced another important proposition into this theory: cells arise only by dividing the original cell, that is, cells are formed only from cells (“cell from cell”).

Since the creation of the cell theory, the doctrine of the cell as a unit of the structure, function and development of the organism has been continuously developed. By the end of the 19th century, thanks to the advances in microscopic technology, the structure of the cell was clarified, organelles were described - parts of the cell that perform various functions, methods for the formation of new cells (mitosis, meiosis) were studied, and the paramount importance of cellular structures in the transfer of hereditary properties became clear. The use of the latest physical and chemical research methods made it possible to delve into the processes of storage and transmission of hereditary information, as well as to study the fine structure of each of the cell structures. All this contributed to the separation of the science of the cell into an independent branch of knowledge - cytology.

The cellular structure of organisms, the similarity of the structure of the cells of all organisms - the basis of the unity of the organic world, evidence of the relationship of living nature

All currently known living organisms (plants, animals, fungi and bacteria) have a cellular structure. Even viruses that do not have a cellular structure can only reproduce in cells. A cell is an elementary structural and functional unit of the living, which is inherent in all its manifestations, in particular, metabolism and energy conversion, homeostasis, growth and development, reproduction and irritability. At the same time, it is in the cells that hereditary information is stored, processed and realized.

Despite all the diversity of cells, the structural plan for them is the same: they all contain hereditary apparatusimmersed in cytoplasm, and the surrounding cell plasma membrane.

The cell arose as a result of a long evolution of the organic world. The unification of cells into a multicellular organism is not a simple summation, since each cell, while retaining all the characteristics inherent in a living organism, at the same time acquires new properties due to the performance of a certain function by it. On the one hand, a multicellular organism can be divided into its constituent parts - cells, but on the other hand, putting them together again, it is impossible to restore the functions of an integral organism, since new properties appear only in the interaction of parts of the system. This manifests one of the main patterns that characterize the living, the unity of the discrete and the integral. The small size and a significant number of cells create a large surface area in multicellular organisms, which is necessary to ensure a rapid metabolism. In addition, in the event of the death of one part of the body, its integrity can be restored due to the reproduction of cells. Outside the cell, the storage and transmission of hereditary information, the storage and transfer of energy with its subsequent transformation into work are impossible. Finally, the division of functions between cells in a multicellular organism provided ample opportunities for organisms to adapt to their environment and was a prerequisite for the complication of their organization.

Thus, the establishment of the unity of the plan of the structure of the cells of all living organisms served as proof of the unity of the origin of all life on Earth.

variety of cells. Prokaryotic and eukaryotic cells. Comparative characteristics of cells of plants, animals, bacteria, fungi Diversity of cells

According to the cellular theory, a cell is the smallest structural and functional unit of organisms, which has all the properties of a living thing. According to the number of cells, organisms are divided into unicellular and multicellular. Cells of unicellular organisms exist as independent organisms and carry out all the functions of a living thing. All prokaryotes and a number of eukaryotes (many species of algae, fungi and protozoa) are unicellular, which amaze with an extraordinary variety of shapes and sizes. However, most organisms are still multicellular. Their cells are specialized in performing certain functions and form tissues and organs, which cannot but be reflected in morphological features. For example, the human body is formed from about 10 14 cells, represented by about 200 species, having a wide variety of shapes and sizes.

The shape of the cells can be round, cylindrical, cubic, prismatic, disc-shaped, spindle-shaped, stellate, etc. and stellate - cells nervous tissue. A number of cells do not have a permanent shape at all. These include, first of all, blood leukocytes.

Cell sizes also vary significantly: most cells of a multicellular organism have sizes from 10 to 100 microns, and the smallest - 2-4 microns. The lower limit is due to the fact that the cell must have a minimum set of substances and structures to ensure life, and too large cells will interfere with the exchange of substances and energy with the environment, and will also impede the processes of maintaining homeostasis. However, some cells can be seen with the naked eye. First of all, these include the cells of the fruits of watermelon and apple trees, as well as the eggs of fish and birds. Even if one of the linear dimensions of the cell exceeds the average, all the rest correspond to the norm. For example, a neuron outgrowth may exceed 1 m in length, but its diameter will still correspond to the average value. There is no direct relationship between cell size and body size. So, the muscle cells of an elephant and a mouse are the same size.

Prokaryotic and eukaryotic cells

As mentioned above, cells have many similar functional properties and morphological features. Each of them consists of a cytoplasm immersed in it hereditary apparatus, and separated from the external environment plasma membrane, or plasmalemma, which does not interfere with the process of metabolism and energy. Outside of the membrane, the cell may also have a cell wall, consisting of various substances, which serves to protect the cell and is a kind of its external skeleton.

The cytoplasm is the entire contents of the cell that fills the space between the plasma membrane and the structure containing genetic information. It consists of the main substance - hyaloplasm- and organelles and inclusions immersed in it. Organelles- these are permanent components of the cell that perform certain functions, and inclusions are components that appear and disappear during the life of the cell, performing mainly storage or excretory functions. Inclusions are often divided into solid and liquid. Solid inclusions are mainly represented by granules and can be of a different nature, while vacuoles and fat drops are considered as liquid inclusions.

Currently, there are two main types of cell organization: prokaryotic and eukaryotic.

A prokaryotic cell does not have a nucleus; its genetic information is not separated from the cytoplasm by membranes.

The region of the cytoplasm that stores genetic information in a prokaryotic cell is called nucleoid. in the cytoplasm prokaryotic cells there is mainly one type of organelle - ribosomes, and organelles surrounded by membranes are absent altogether. Bacteria are prokaryotes.

A eukaryotic cell is a cell in which, at least at one of the stages of development, there is core- a special structure in which DNA is located.

The cytoplasm of eukaryotic cells is distinguished by a significant variety of membrane and non-membrane organelles. Eukaryotic organisms include plants, animals and fungi. The size of prokaryotic cells, as a rule, is an order of magnitude smaller than the size of eukaryotic cells. Most prokaryotes are single-celled organisms, while eukaryotes are multicellular.

Comparative characteristics of the structure of cells of plants, animals, bacteria and fungi

In addition to the features characteristic of prokaryotes and eukaryotes, the cells of plants, animals, fungi and bacteria have a number of other features. So, plant cells contain specific organelles - chloroplasts, which determine their ability to photosynthesis, while in other organisms these organelles are not found. Of course, this does not mean that other organisms are not capable of photosynthesis, since, for example, in bacteria, it occurs on invaginations of the plasmalemma and individual membrane vesicles in the cytoplasm.

Plant cells usually contain large vacuoles filled with cell sap. In the cells of animals, fungi and bacteria, they are also found, but they have a completely different origin and perform different functions. The main reserve substance found in the form of solid inclusions is starch in plants, glycogen in animals and fungi, and glycogen or volutin in bacteria.

Another hallmark of these groups of organisms is the organization of the surface apparatus: the cells of animal organisms do not have a cell wall, their plasma membrane is covered only with a thin glycocalyx, while all the rest have it. This is entirely understandable, since the way animals feed is associated with the capture of food particles in the process of phagocytosis, and the presence of a cell wall would deprive them of this opportunity. The chemical nature of the substance that makes up the cell wall is not the same in different groups of living organisms: if in plants it is cellulose, then in fungi it is chitin, and in bacteria it is murein. Comparative characteristics cell structures of plants, animals, fungi and bacteria

sign	bacteria	Animals	Mushrooms	Plants
Feeding method	heterotrophic or autotrophic	Heterotrophic	Heterotrophic	autotrophic
Organization of hereditary information	prokaryotes	eukaryotes	eukaryotes	eukaryotes
DNA localization	Nucleoid, plasmids	nucleus, mitochondria	nucleus, mitochondria	Nucleus, mitochondria, plastids
plasma membrane	Eat	Eat	Eat	Eat
cell wall	Mureinovaya	—	Chitinous	Cellulosic
Cytoplasm	Eat	Eat	Eat	Eat
Organelles	Ribosomes	Membrane and non-membrane, including the cell center	Membrane and non-membrane	Membrane and non-membrane, including plastids
Organelles of movement	Flagella and villi	Flagella and cilia	Flagella and cilia	Flagella and cilia
Vacuoles	Rarely	contractile, digestive	Sometimes	central vacuole with cell sap
Inclusions	Glycogen, volutin	Glycogen	Glycogen	Starch

Differences in the structure of cells of representatives of different kingdoms of wildlife are shown in the figure.

The chemical composition of the cell. Macro- and microelements. The relationship of the structure and functions of inorganic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. The role of chemicals in the cell and the human body

The chemical composition of the cell

In the composition of living organisms, most of the chemical elements of the Periodic Table of Elements of D. I. Mendeleev, discovered to date, have been found. On the one hand, they do not contain a single element that would not be in inanimate nature, and on the other hand, their concentrations in bodies of inanimate nature and living organisms differ significantly.

These chemical elements form inorganic and organic substances. Despite the fact that inorganic substances predominate in living organisms, it is organic substances that determine the uniqueness of their chemical composition and the phenomenon of life in general, since they are synthesized mainly by organisms in the process of vital activity and play an important role in reactions.

Science deals with the study of the chemical composition of organisms and the chemical reactions that take place in them. biochemistry.

It should be noted that the content of chemicals in different cells and tissues can vary significantly. For example, while proteins predominate among organic compounds in animal cells, carbohydrates predominate in plant cells.

Chemical element	Earth's crust	Sea water	Alive organisms
O	49.2	85.8	65-75
C	0.4	0.0035	15-18
H	1.0	10.67	8-10
N	0.04	0.37	1.5-3.0
P	0.1	0.003	0.20-1.0
S	0.15	0.09	0.15-0.2
K	2.35	0.04	0.15-0.4
Ca	3.25	0.05	0.04-2.0
Cl	0.2	0.06	0.05-0.1
mg	2.35	0.14	0.02-0.03
Na	2.4	1.14	0.02-0.03
Fe	4.2	0.00015	0.01-0.015
Zn	< 0.01	0.00015	0.0003
Cu	< 0.01	< 0.00001	0.0002
I	< 0.01	0.000015	0.0001
F	0.1	2.07	0.0001

Macro- and microelements

About 80 chemical elements are found in living organisms, but only 27 of these elements have their functions in the cell and organism. The rest of the elements are present in trace amounts, and appear to be ingested through food, water, and air. The content of chemical elements in the body varies significantly. Depending on the concentration, they are divided into macronutrients and microelements.

The concentration of each macronutrients in the body exceeds 0.01%, and their total content is 99%. Macronutrients include oxygen, carbon, hydrogen, nitrogen, phosphorus, sulfur, potassium, calcium, sodium, chlorine, magnesium, and iron. The first four of these elements (oxygen, carbon, hydrogen and nitrogen) are also called organogenic, since they are part of the main organic compounds. Phosphorus and sulfur are also components of a number of organic substances, such as proteins and nucleic acids. Phosphorus is essential for the formation of bones and teeth.

Without the remaining macronutrients, the normal functioning of the body is impossible. So, potassium, sodium and chlorine are involved in the processes of excitation of cells. Potassium is also needed for many enzymes to function and to retain water in the cell. Calcium is found in the cell walls of plants, bones, teeth, and mollusk shells, and is required for muscle contraction and intracellular movement. Magnesium is a component of chlorophyll - the pigment that ensures the flow of photosynthesis. It also takes part in protein biosynthesis. Iron, in addition to being a part of hemoglobin, which carries oxygen in the blood, is necessary for the processes of respiration and photosynthesis, as well as for the functioning of many enzymes.

trace elements are contained in the body in concentrations of less than 0.01%, and their total concentration in the cell does not even reach 0.1%. Trace elements include zinc, copper, manganese, cobalt, iodine, fluorine, etc. Zinc is part of the pancreatic hormone molecule insulin, copper is required for photosynthesis and respiration. Cobalt is a component of vitamin B12, the absence of which leads to anemia. Iodine is necessary for the synthesis of thyroid hormones, which ensure the normal course of metabolism, and fluorine is associated with the formation of tooth enamel.

Both deficiency and excess or disturbance of the metabolism of macro- and microelements lead to the development of various diseases. In particular, a lack of calcium and phosphorus causes rickets, a lack of nitrogen causes severe protein deficiency, an iron deficiency causes anemia, and a lack of iodine causes a violation of the formation of thyroid hormones and a decrease in metabolic rate. Reducing the intake of fluoride with water and food to a large extent causes a violation of the renewal of tooth enamel and, as a result, a predisposition to caries. Lead is toxic to almost all organisms. Its excess causes irreversible damage to the brain and central nervous system which is manifested by loss of vision and hearing, insomnia, kidney failure, convulsions, and can also lead to paralysis and diseases such as cancer. Acute lead poisoning is accompanied by sudden hallucinations and ends in coma and death.

The lack of macro- and microelements can be compensated by increasing their content in food and drinking water as well as by taking medications. So, iodine is found in seafood and iodized salt, calcium in eggshells, etc.

The relationship of the structure and functions of inorganic and organic substances (proteins, nucleic acids, carbohydrates, lipids, ATP) that make up the cell. The role of chemicals in the cell and the human body

inorganic substances

The chemical elements of the cell form various compounds - inorganic and organic. The inorganic substances of the cell include water, mineral salts, acids, etc., and the organic substances include proteins, nucleic acids, carbohydrates, lipids, ATP, vitamins, etc.

Water(H 2 O) - the most common inorganic substance of the cell, which has unique physical and chemical properties. It has no taste, no color, no smell. Density and viscosity of all substances are estimated by water. Like many other substances, water can be in three states of aggregation: solid (ice), liquid and gaseous (steam). The melting point of water is $0°$C, the boiling point is $100°$C, however, the dissolution of other substances in water can change these characteristics. The heat capacity of water is also quite high - 4200 kJ / mol K, which makes it possible for it to take part in the processes of thermoregulation. In a water molecule, hydrogen atoms are located at an angle of $105°$, while the common electron pairs are pulled away by the more electronegative oxygen atom. This determines the dipole properties of water molecules (one of their ends is positively charged and the other negatively) and the possibility of formation of hydrogen bonds between water molecules. The adhesion of water molecules underlies the phenomenon of surface tension, capillarity and the properties of water as a universal solvent. As a result, all substances are divided into soluble in water (hydrophilic) and insoluble in it (hydrophobic). Thanks to these unique properties, it is predetermined that water has become the basis of life on Earth.

The average water content in the cells of the body is not the same and may change with age. So, in a one and a half month old human embryo, the water content in the cells reaches 97.5%, in an eight month old - 83%, in a newborn it decreases to 74%, and in an adult it averages 66%. However, body cells differ in water content. So, the bones contain about 20% water, the liver - 70%, and the brain - 86%. On the whole, it can be said that the concentration of water in cells is directly proportional to the metabolic rate.

mineral salts may be in dissolved or undissolved states. Soluble salts dissociate into ions - cations and anions. The most important cations are potassium and sodium ions, which facilitate the transfer of substances across the membrane and participate in the occurrence and conduction of a nerve impulse; as well as calcium ions, which takes part in the processes of contraction of muscle fibers and blood clotting; magnesium, which is part of chlorophyll; iron, which is part of a number of proteins, including hemoglobin. The most important anions are the phosphate anion, which is part of ATP and nucleic acids, and the carbonic acid residue, which softens fluctuations in the pH of the medium. Ions of mineral salts provide both the penetration of the water itself into the cell and its retention in it. If the concentration of salts in the environment is lower than in the cell, then water penetrates into the cell. Ions also determine the buffer properties of the cytoplasm, i.e., its ability to maintain a constant slightly alkaline pH of the cytoplasm, despite the constant formation of acidic and alkaline products in the cell.

Insoluble salts(CaCO 3, Ca 3 (PO 4) 2, etc.) are part of the bones, teeth, shells and shells of unicellular and multicellular animals.

In addition, other inorganic compounds, such as acids and oxides, can be produced in organisms. So, parietal cells of the human stomach produce hydrochloric acid, which activates the digestive enzyme pepsin, and silicon oxide impregnates the cell walls of horsetails and forms diatom shells. In recent years, the role of nitric oxide (II) in signaling in cells and the body has also been investigated.

organic matter

General characteristics of the organic substances of the cell

The organic substances of a cell can be represented by both relatively simple molecules and more complex ones. In cases where a complex molecule (macromolecule) is formed by a significant number of repeating simpler molecules, it is called polymer, and structural units - monomers. Depending on whether the units of polymers are repeated or not, they are classified as regular or irregular. Polymers make up to 90% of the dry matter mass of the cell. They belong to three main classes of organic compounds - carbohydrates (polysaccharides), proteins and nucleic acids. Regular polymers are polysaccharides, while proteins and nucleic acids are irregular. In proteins and nucleic acids, the sequence of monomers is extremely important, since they perform an informational function.

Carbohydrates

Carbohydrates- these are organic compounds, which mainly include three chemical elements - carbon, hydrogen and oxygen, although a number of carbohydrates also contain nitrogen or sulfur. The general formula for carbohydrates is C m (H 2 O) n. They are divided into simple and complex carbohydrates.

Simple carbohydrates (monosaccharides) contain a single sugar molecule that cannot be broken down into simpler ones. These are crystalline substances, sweet in taste and highly soluble in water. Monosaccharides take an active part in the metabolism in the cell and are part of complex carbohydrates - oligosaccharides and polysaccharides.

Monosaccharides are classified by the number of carbon atoms (C 3 -C 9), for example, pentoses(C 5) and hexoses(From 6). Pentoses include ribose and deoxyribose. Ribose is part of RNA and ATP. Deoxyribose is a component of DNA. Hexoses (C 6 H 12 O 6) are glucose, fructose, galactose, etc. Glucose(grape sugar) is found in all organisms, including human blood, as it is an energy reserve. It is part of many complex sugars: sucrose, lactose, maltose, starch, cellulose, etc. Fructose(fruit sugar) highest concentrations found in fruits, honey, sugar beet roots. It not only takes an active part in metabolic processes, but also is part of sucrose and some polysaccharides, such as insulin.

Most monosaccharides are able to give a silver mirror reaction and reduce copper by adding Fehling's liquid (a mixture of solutions of copper (II) sulfate and potassium-sodium tartrate) and boiling.

TO oligosaccharides include carbohydrates formed by several monosaccharide residues. They are generally also highly soluble in water and are sweet in taste. Depending on the number of these residues, disaccharides (two residues), trisaccharides (three), etc. are distinguished. Disaccharides include sucrose, lactose, maltose, etc. sucrose(beet or cane sugar) consists of residues of glucose and fructose, it is found in the storage organs of some plants. Especially a lot of sucrose in the roots of sugar beet and sugar cane, where they are obtained in an industrial way. It serves as a benchmark for the sweetness of carbohydrates. Lactose, or milk sugar , formed by residues of glucose and galactose, found in maternal and cow's milk. Maltose(malt sugar) consists of two glucose residues. It is formed during the breakdown of polysaccharides in plant seeds and in digestive system man, is used in the production of beer.

Polysaccharides are biopolymers whose monomers are mono- or disaccharide residues. Most polysaccharides are insoluble in water and taste unsweetened. These include starch, glycogen, cellulose and chitin. Starch- This is a white powdery substance that is not wetted by water, but forms a suspension when brewed with hot water - a paste. Starch is actually made up of two polymers, the less branched amylose and the more branched amylopectin (Figure 2.9). The monomer of both amylose and amylopectin is glucose. Starch is the main reserve substance of plants, which accumulates in large quantities in seeds, fruits, tubers, rhizomes and other storage organs of plants. A qualitative reaction to starch is a reaction with iodine, in which the starch turns blue-violet.

Glycogen(animal starch) is a reserve polysaccharide of animals and fungi, which in humans accumulates in the largest quantities in the muscles and liver. It is also insoluble in water and tastes unsweetened. The monomer of glycogen is glucose. Compared to starch molecules, glycogen molecules are even more branched.

Cellulose, or cellulose, - the main reference polysaccharide of plants. The monomer of cellulose is glucose. Unbranched cellulose molecules form bundles that are part of the cell walls of plants. Cellulose is the basis of wood, it is used in construction, in the production of textiles, paper, alcohol and many organic substances. Cellulose is chemically inert and does not dissolve in either acids or alkalis. It is also not broken down by the enzymes of the human digestive system, but bacteria in the large intestine help digest it. In addition, fiber stimulates wall contractions. gastrointestinal tract helping to improve its performance.

Chitin is a polysaccharide, the monomer of which is a nitrogen-containing monosaccharide. It is part of the cell walls of fungi and arthropod shells. In the human digestive system, there is also no enzyme for digesting chitin, only some bacteria have it.

Functions of carbohydrates. Carbohydrates perform plastic (construction), energy, storage and support functions in the cell. They form the cell walls of plants and fungi. The energy value of the breakdown of 1 g of carbohydrates is 17.2 kJ. Glucose, fructose, sucrose, starch and glycogen are reserve substances. Carbohydrates can also be part of complex lipids and proteins, forming glycolipids and glycoproteins, in particular in cell membranes. No less important is the role of carbohydrates in the intercellular recognition and perception of environmental signals, since they act as receptors in the composition of glycoproteins.

Lipids

Lipids is a chemically heterogeneous group of low molecular weight substances with hydrophobic properties. These substances are insoluble in water, form emulsions in it, but are readily soluble in organic solvents. Lipids are oily to the touch, many of them leave characteristic non-drying traces on paper. Together with proteins and carbohydrates, they are one of the main components of cells. The content of lipids in different cells is not the same, especially a lot of them in the seeds and fruits of some plants, in the liver, heart, blood.

Depending on the structure of the molecule, lipids are divided into simple and complex. TO simple lipids include neutral lipids (fats), waxes and steroids. Complex lipids also contain another, non-lipid component. The most important of them are phospholipids, glycolipids, etc.

Fats are esters of the trihydric alcohol glycerol and higher fatty acids. Most fatty acids contain 14-22 carbon atoms. Among them there are both saturated and unsaturated, that is, containing double bonds. Of the saturated fatty acids, palmitic and stearic acids are most common, and of the unsaturated fatty acids, oleic. Some unsaturated fatty acid are not synthesized in the human body or are synthesized in insufficient quantities, and therefore are irreplaceable. Glycerol residues form hydrophilic heads, while fatty acid residues form hydrophobic tails.

Fats perform mainly a storage function in cells and serve as a source of energy. They are rich in subcutaneous fatty tissue, which performs shock-absorbing and thermal insulation functions, and in aquatic animals it also increases buoyancy. Plant fats mostly contain unsaturated fatty acids, as a result of which they are liquid and are called oils. Oils are found in the seeds of many plants, such as sunflower, soybeans, rapeseed, etc.

Waxes are esters and mixtures of fatty acids and fatty alcohols. In plants, they form a film on the surface of the leaf, which protects against evaporation, the penetration of pathogens, etc. In a number of animals, they cover the body or serve to build honeycombs.

TO steroids include lipids such as cholesterol, an essential component of cell membranes, as well as sex hormones estradiol, testosterone, vitamin D, etc.

Phospholipids, in addition to residues of glycerol and fatty acids, contain a residue of orthophosphoric acid. They are part of cell membranes and provide their barrier properties.

Glycolipids are also components of membranes, but their content there is low. The non-lipid part of glycolipids are carbohydrates.

Functions of lipids. Lipids perform plastic (building), energy, storage, protective, excretory and regulatory functions in the cell, in addition, they are vitamins. It is an essential component of cell membranes. When splitting 1 g of lipids, 38.9 kJ of energy is released. They are stored in various bodies plants and animals. In addition, subcutaneous fatty tissue protects internal organs from hypothermia or overheating, as well as shock. The regulatory function of lipids is due to the fact that some of them are hormones. The fat body of insects serves for excretion.

Squirrels

Squirrels- These are high-molecular compounds, biopolymers, the monomers of which are amino acids linked by peptide bonds.

amino acid called an organic compound having an amino group, a carboxyl group and a radical. In total, about 200 amino acids are found in nature, which differ in radicals and the mutual arrangement of functional groups, but only 20 of them can be part of proteins. These amino acids are called proteinogenic.

Unfortunately, not all proteinogenic amino acids can be synthesized in the human body, so they are divided into interchangeable and irreplaceable. Non-essential amino acids are formed in the human body in the required amount, and irreplaceable- No. They must come from food, but can also be partially synthesized by intestinal microorganisms. There are 8 fully essential amino acids. These include valine, isoleucine, leucine, lysine, methionine, threonine, tryptophan, and phenylalanine. Despite the fact that absolutely all proteinogenic amino acids are synthesized in plants, vegetable proteins are incomplete because they do not contain a complete set of amino acids, moreover, the presence of protein in the vegetative parts of plants rarely exceeds 1-2% of the mass. Therefore, it is necessary to eat proteins not only of vegetable, but also of animal origin.

A sequence of two amino acids linked by peptide bonds is called dipeptide, out of three tripeptide etc. Among the peptides there are such important compounds as hormones (oxytocin, vasopressin), antibiotics, etc. A chain of more than twenty amino acids is called polypeptide, and polypeptides containing more than 60 amino acid residues are proteins.

Levels structural organization squirrel. Proteins can have primary, secondary, tertiary and quaternary structures.

Primary structure of a protein- This linear amino acid sequence linked by a peptide bond. The primary structure ultimately determines the specificity of the protein and its uniqueness, since even if we assume that the average protein contains 500 amino acid residues, then the number of possible combinations is 20,500. Therefore, a change in the location of at least one amino acid in the primary structure entails a change secondary and higher structures, as well as the properties of the protein as a whole.

Structural features of the protein determine its spatial packing - the emergence of secondary and tertiary structures.

secondary structure is the spatial arrangement of a protein molecule in the form spirals or folds held by hydrogen bonds between the oxygen and hydrogen atoms of peptide groups of different turns of the helix or folds. Many proteins contain more or less long regions with a secondary structure. These are, for example, keratins of hair and nails, silk fibroin.

Tertiary structure squirrel ( globule) is also a form of spatial folding of the polypeptide chain, held by hydrophobic, hydrogen, disulfide (S-S) and other bonds. It is characteristic of most body proteins, such as muscle myoglobin.

Quaternary structure- the most complex, formed by several polypeptide chains connected mainly by the same bonds as in the tertiary (hydrophobic, ionic and hydrogen), as well as other weak interactions. The quaternary structure is characteristic of a few proteins, such as hemoglobin, chlorophyll, etc.

The shape of the molecule is fibrillar And globular proteins. The first of them are elongated, like, for example, connective tissue collagen or hair and nail keratins. Globular proteins are in the form of a ball (globules), like muscle myoglobin.

Simple and complex proteins. Proteins can be simple And complex. Simple proteins are made up of only amino acids, while complex proteins (lipoproteins, chromoproteins, glycoproteins, nucleoproteins, etc.) contain protein and non-protein parts. Chromoproteins contain a colored non-protein portion. These include hemoglobin, myoglobin, chlorophyll, cytochromes, etc. Thus, in the composition of hemoglobin, each of the four polypeptide chains of the globin protein is associated with a non-protein part - heme, in the center of which there is an iron ion, which gives hemoglobin a red color. Non-protein part lipoproteins is a lipid and glycoproteins- carbohydrate. Both lipoproteins and glycoproteins are part of cell membranes. Nucleoproteins are complexes of proteins and nucleic acids (DNA and RNA). They perform the most important functions in the processes of storage and transmission of hereditary information.

Protein properties. Many proteins are highly soluble in water, but there are some among them that dissolve only in solutions of salts, alkalis, acids, or organic solvents. The structure of a protein molecule and its functional activity depend on environmental conditions. The loss of a protein molecule of its structure while maintaining the primary is called denaturation.

Denaturation occurs due to changes in temperature, pH, atmospheric pressure, under the action of acids, alkalis, salts heavy metals, organic solvents, etc. The reverse process of restoring secondary and higher structures is called renaturation, however, it is not always possible. The complete breakdown of a protein molecule is called destruction.

Protein functions. Proteins perform a number of functions in the cell: plastic (construction), catalytic (enzymatic), energy, signal (receptor), contractile (motor), transport, protective, regulatory and storage.

The building function of proteins is associated with their presence in cell membranes and structural components of the cell. Energy - due to the fact that during the breakdown of 1 g of protein, 17.2 kJ of energy is released. Membrane receptor proteins are actively involved in the perception of environmental signals and their transmission through the cell, as well as in intercellular recognition. Without proteins, the movement of cells and organisms as a whole is impossible, since they form the basis of flagella and cilia, and also provide muscle contraction and movement of intracellular components. In the blood of humans and many animals, the protein hemoglobin carries oxygen and part of carbon dioxide, while other proteins transport ions and electrons. The protective role of proteins is associated primarily with immunity, since the interferon protein is able to destroy many viruses, and antibody proteins inhibit the development of bacteria and other foreign agents. There are many hormones among proteins and peptides, for example, the pancreatic hormone insulin, which regulates the concentration of glucose in the blood. In some organisms, proteins can be stored in reserve, as in legumes in seeds, or the proteins of a chicken egg.

Nucleic acids

Nucleic acids are biopolymers whose monomers are nucleotides. Currently, two types of nucleic acids are known: ribonucleic (RNA) and deoxyribonucleic (DNA).

Nucleotide formed by a nitrogenous base, a pentose sugar residue and a phosphoric acid residue. The features of nucleotides are mainly determined by the nitrogenous bases that make up their composition, therefore, even conditionally, nucleotides are designated by the first letters of their names. The composition of nucleotides can include five nitrogenous bases: adenine (A), guanine (G), thymine (T), uracil (U) and cytosine (C). Nucleotide pentoses - ribose and deoxyribose - determine which nucleotide will be formed - ribonucleotide or deoxyribonucleotide. Ribonucleotides are RNA monomers, they can act as signal molecules (cAMP) and be part of high-energy compounds, such as ATP, and coenzymes, such as NADP, NAD, FAD, etc., and deoxyribonucleotides are part of DNA.

Deoxyribonucleic acid (DNA)- double-stranded biopolymer, the monomers of which are deoxyribonucleotides. The composition of deoxyribonucleotides includes only four nitrogenous bases out of five possible - adenine (A), thymine (T), guanine (G) or cytosine (C), as well as deoxyribose and phosphoric acid residues. Nucleotides in the DNA chain are interconnected through orthophosphoric acid residues, forming a phosphodiester bond. When a double-stranded molecule is formed, the nitrogenous bases are directed inward of the molecule. However, the connection of DNA chains does not occur randomly - the nitrogenous bases of different chains are interconnected by hydrogen bonds according to the principle of complementarity: adenine is connected to thymine by two hydrogen bonds (A \u003d T), and guanine and cytosine by three (G $ ≡ $ C).

For her were set Chargaff rules:

1. The number of DNA nucleotides containing adenine is equal to the number of nucleotides containing thymine (A=T).
2. The number of DNA nucleotides containing guanine is equal to the number of nucleotides containing cytosine (G$≡$C).
3. The sum of deoxyribonucleotides containing adenine and guanine is equal to the sum of deoxyribonucleotides containing thymine and cytosine (A+G = T+C).
4. The ratio of the sum of deoxyribonucleotides containing adenine and thymine to the sum of deoxyribonucleotides containing guanine and cytosine depends on the type of organism.

The structure of DNA was deciphered by F. Crick and D. Watson ( Nobel Prize in Physiology or Medicine, 1962). According to their model, the DNA molecule is a right-handed double helix. The distance between nucleotides in the DNA chain is 0.34 nm.

The most important property of DNA is the ability to replicate (self-doubling). The main function of DNA is the storage and transmission of hereditary information, which is written in the form of nucleotide sequences. The stability of the DNA molecule is maintained by powerful repair (recovery) systems, but even they are not able to completely eliminate adverse effects, which ultimately leads to mutations. The DNA of eukaryotic cells is concentrated in the nucleus, mitochondria and plastids, while prokaryotic cells are located directly in the cytoplasm. Nuclear DNA is the basis of chromosomes, it is represented by open molecules. DNA of mitochondria, plastids and prokaryotes has a circular shape.

Ribonucleic acid (RNA)- a biopolymer whose monomers are ribonucleotides. They also contain four nitrogenous bases - adenine (A), uracil (U), guanine (G) or cytosine (C), thereby differing from DNA in one of the bases (instead of thymine, RNA contains uracil). The pentose sugar residue in ribonucleotides is represented by ribose. RNA is mostly single-stranded molecules, with the exception of some viral ones. There are three main types of RNA: informational, or template (mRNA, mRNA), ribosomal (rRNA) and transport (tRNA). All of them are formed in the process transcriptions- rewriting from DNA molecules.

And RNAs make up the smallest RNA fraction in a cell (2-4%), which is offset by their diversity, since one cell can contain thousands of different mRNAs. These are single-stranded molecules that are templates for the synthesis of polypeptide chains. Information about the structure of the protein is recorded in them in the form of sequences of nucleotides, and each amino acid encodes a triplet of nucleotides - codon.

R RNA is the most numerous type of RNA in the cell (up to 80%). Their molecular weight averages 3000-5000; are formed in the nucleoli and are part of the cellular organelles - ribosomes. rRNAs also appear to play a role in protein synthesis.

T RNA is the smallest of the RNA molecules, as it contains only 73-85 nucleotides. Their share of the total amount of cell RNA is about 16%. The function of tRNA is the transport of amino acids to the site of protein synthesis (on ribosomes). The shape of the tRNA molecule resembles a clover leaf. At one end of the molecule there is a site for attaching an amino acid, and in one of the loops there is a triplet of nucleotides that is complementary to the mRNA codon and determines which amino acid the tRNA will carry - anticodon.

All types of RNA take an active part in the process of realizing hereditary information, which is rewritten from DNA to mRNA, and on the latter protein synthesis is carried out. tRNA in the process of protein synthesis delivers amino acids to ribosomes, and rRNA is part of the ribosomes directly.

Adenosine triphosphoric acid (ATP) is a nucleotide containing, in addition to the nitrogenous base of adenine and a ribose residue, three phosphoric acid residues. The bonds between the last two phosphorus residues are macroergic (42 kJ / mol of energy is released during splitting), while the standard chemical bond during splitting gives 12 kJ / mol. If energy is needed, the macroergic bond of ATP is split, adenosine diphosphoric acid (ADP), a phosphorus residue are formed, and energy is released:

ATP + H 2 O $→$ ADP + H 3 PO 4 + 42 kJ.

ADP can also be broken down to form AMP (adenosine monophosphoric acid) and a phosphoric acid residue:

ADP + H 2 O $→$ AMP + H 3 PO 4 + 42 kJ.

In the process of energy metabolism (during respiration, fermentation), as well as in the process of photosynthesis, ADP attaches a phosphorus residue and turns into ATP. The ATP recovery reaction is called phosphorylation. ATP is a universal source of energy for all life processes of living organisms.

The study of the chemical composition of the cells of all living organisms has shown that they contain the same chemical elements, chemicals that perform the same functions. Moreover, a piece of DNA transferred from one organism to another will work in it, and a protein synthesized by bacteria or fungi will act as a hormone or enzyme in the human body. This is one of the proofs of the unity of the origin of the organic world.

Cell structure. The relationship of the structure and functions of the parts and organelles of the cell is the basis of its integrity

Cell structure

The structure of prokaryotic and eukaryotic cells

The main structural components of cells are the plasma membrane, cytoplasm and hereditary apparatus. Depending on the characteristics of the organization, two main types of cells are distinguished: prokaryotic and eukaryotic. The main difference between prokaryotic and eukaryotic cells is the organization of their hereditary apparatus: in prokaryotes it is located directly in the cytoplasm (this area of ​​the cytoplasm is called nucleoid) and is not separated from it by membrane structures, while in eukaryotes most of the DNA is concentrated in the nucleus, surrounded by a double membrane. In addition, the genetic information of prokaryotic cells, located in the nucleoid, is recorded in the circular DNA molecule, while in eukaryotes the DNA molecules are not closed.

Unlike eukaryotes, the cytoplasm of prokaryotic cells also contains a small amount of organelles, while eukaryotic cells are characterized by a significant variety of these structures.

The structure and functions of biological membranes

The structure of the biomembrane. The cell-bounding membranes and membrane organelles of eukaryotic cells share a common chemical composition and structure. They include lipids, proteins and carbohydrates. Membrane lipids are mainly represented by phospholipids and cholesterol. Most membrane proteins are complex proteins such as glycoproteins. Carbohydrates do not occur on their own in the membrane, they are associated with proteins and lipids. The thickness of the membranes is 7-10 nm.

According to the currently accepted fluid mosaic model of membrane structure, lipids form a double layer, or lipid bilayer, in which the hydrophilic "heads" of lipid molecules are turned outward, and the hydrophobic "tails" are hidden inside the membrane. These “tails”, due to their hydrophobicity, ensure the separation of the aqueous phases of the internal environment of the cell and its environment. Proteins are associated with lipids through various types of interactions. Some of the proteins are located on the surface of the membrane. Such proteins are called peripheral, or superficial. Other proteins are partially or completely immersed in the membrane - these are integral, or submerged proteins. Membrane proteins perform structural, transport, catalytic, receptor and other functions.

Membranes are not like crystals, their components are constantly in motion, as a result of which gaps appear between lipid molecules - pores through which they can enter or leave the cell various substances.

Biological membranes differ in their location in the cell, their chemical composition, and their functions. The main types of membranes are plasma and internal. plasma membrane contains about 45% lipids (including glycolipids), 50% proteins and 5% carbohydrates. Chains of carbohydrates that make up complex proteins-glycoproteins and complex lipids-glycolipids protrude above the surface of the membrane. Plasmalemma glycoproteins are extremely specific. So, for example, through them there is a mutual recognition of cells, including sperm and eggs.

On the surface of animal cells, carbohydrate chains form a thin surface layer - glycocalyx. It has been found in almost all animal cells, but its severity is not the same (10-50 microns). The glycocalyx provides a direct connection of the cell with the external environment; extracellular digestion occurs in it; receptors are located in the glycocalyx. The cells of bacteria, plants and fungi, in addition to the plasmalemma, are also surrounded by cell membranes.

Internal membranes eukaryotic cells delimit different parts of the cell, forming a kind of "compartments" - compartments, which contributes to the separation of various processes of metabolism and energy. They may differ in chemical composition and functions, but they retain the general plan of the structure.

Membrane functions:

1. Limiting. It consists in the fact that they separate the internal space of the cell from the external environment. The membrane is semi-permeable, that is, only those substances that are necessary for the cell can freely overcome it, while there are mechanisms for transporting the necessary substances.
2. Receptor. It is associated primarily with the perception of environmental signals and the transfer of this information into the cell. Special receptor proteins are responsible for this function. Membrane proteins are also responsible for cellular recognition according to the "friend or foe" principle, as well as for the formation of intercellular connections, the most studied of which are the synapses of nerve cells.
3. catalytic. Numerous enzyme complexes are located on the membranes, as a result of which intensive synthetic processes take place on them.
4. Energy transforming. Associated with the formation of energy, its storage in the form of ATP and expenditure.
5. Compartmentalization. The membranes also delimit the space inside the cell, thereby separating the initial substances of the reaction and the enzymes that can carry out the corresponding reactions.
6. Formation of intercellular contacts. Despite the fact that the membrane thickness is so small that it cannot be distinguished with the naked eye, on the one hand, it serves as a fairly reliable barrier for ions and molecules, especially water-soluble ones, and on the other hand, it ensures their transfer into the cell and out.
7. Transport.

membrane transport. Due to the fact that cells as elementary biological systems are open systems, to ensure metabolism and energy, maintain homeostasis, growth, irritability and other processes, the transfer of substances through the membrane is required - membrane transport. Currently, the transport of substances across the cell membrane is divided into active, passive, endo- and exocytosis.

Passive transport is a type of transport that occurs without the expenditure of energy from a higher concentration to a lower one. Lipid-soluble small non-polar molecules (O 2, CO 2) easily penetrate the cell by simple diffusion. Insoluble in lipids, including charged small particles, are picked up by carrier proteins or pass through special channels (glucose, amino acids, K +, PO 4 3-). This type of passive transport is called facilitated diffusion. Water enters the cell through pores in the lipid phase, as well as through special channels lined with proteins. The transport of water across a membrane is called osmosis.

Osmosis is extremely important in the life of the cell, because if it is placed in a solution with a higher concentration of salts than in the cell solution, then water will begin to leave the cell, and the volume of living contents will begin to decrease. In animal cells, the cell as a whole shrinks, and in plant cells, the cytoplasm lags behind the cell wall, which is called plasmolysis. When a cell is placed in a solution less concentrated than the cytoplasm, water is transported in the opposite direction - into the cell. However, there are limits to the extensibility of the cytoplasmic membrane, and the animal cell eventually ruptures, while in the plant cell this is not allowed by a strong cell wall. The phenomenon of filling the entire internal space of the cell with cellular contents is called deplasmolysis. Intracellular salt concentration should be taken into account in the preparation of drugs, especially for intravenous administration, as this can lead to damage to blood cells (for this, saline with a concentration of 0.9% sodium chloride). This is no less important in the cultivation of cells and tissues, as well as organs of animals and plants.

active transport proceeds with the expenditure of ATP energy from a lower concentration of a substance to a higher one. It is carried out with the help of special proteins-pumps. Proteins pump ions K +, Na +, Ca 2+ and others through the membrane, which contributes to the transport of the most important organic substances, as well as the formation nerve impulses etc.

Endocytosis- this is an active process of absorption of substances by the cell, in which the membrane forms invaginations, and then forms membrane vesicles - phagosomes, which contain absorbed objects. The primary lysosome then fuses with the phagosome to form secondary lysosome, or phagolysosome, or digestive vacuole. The contents of the vesicle are cleaved by lysosome enzymes, and the cleavage products are absorbed and assimilated by the cell. Undigested residues are removed from the cell by exocytosis. There are two main types of endocytosis: phagocytosis and pinocytosis.

Phagocytosis is the process of capture by the cell surface and absorption of solid particles by the cell, and pinocytosis- liquids. Phagocytosis occurs mainly in animal cells (single-celled animals, human leukocytes), it provides their nutrition, and often the protection of the body. By way of pinocytosis, the absorption of proteins, antigen-antibody complexes in the process of immune reactions, etc. occurs. However, many viruses also enter the cell by way of pinocytosis or phagocytosis. In the cells of plants and fungi, phagocytosis is practically impossible, since they are surrounded by strong cell membranes.

Exocytosis is the reverse process of endocytosis. Thus, undigested food residues are released from the digestive vacuoles, the substances necessary for the life of the cell and the organism as a whole are removed. For example, the transmission of nerve impulses occurs due to the release of chemical messengers by the neuron that sends the impulse - mediators, and in plant cells, auxiliary carbohydrates of the cell membrane are released in this way.

Cell walls of plant cells, fungi and bacteria. Outside of the membrane, the cell can secrete a strong framework - cell membrane, or cell wall.

In plants, the cell wall is made up of cellulose packed in bundles of 50-100 molecules. The gaps between them are filled with water and other carbohydrates. The plant cell membrane is pierced by tubules - plasmodesmata through which the membranes of the endoplasmic reticulum pass. The plasmodesmata transport substances between cells. However, the transport of substances, such as water, can also occur along the cell walls themselves. Over time, various substances, including tannins or fat-like substances, accumulate in the cell membrane of plants, which leads to lignification or corking of the cell wall itself, the displacement of water and the death of cellular contents. Between the cell walls of neighboring plant cells there are jelly-like pads - middle plates that fasten them together and cement the plant body as a whole. They are destroyed only in the process of fruit ripening and when the leaves fall.

The cell walls of fungal cells are formed chitin- a carbohydrate containing nitrogen. They are strong enough and are the outer skeleton of the cell, but still, like in plants, they prevent phagocytosis.

In bacteria, the cell wall contains a carbohydrate with fragments of peptides - murein, however, its content differs significantly in different groups bacteria. On top of the cell wall, other polysaccharides can also be released, forming a mucous capsule that protects bacteria from external influences.

The shell determines the shape of the cell, serves as a mechanical support, performs a protective function, provides the osmotic properties of the cell, limiting the stretching of the living contents and preventing the rupture of the cell, which increases due to the influx of water. In addition, water and substances dissolved in it overcome the cell wall before entering the cytoplasm or, conversely, when leaving it, while water is transported along the cell walls faster than through the cytoplasm.

Cytoplasm

Cytoplasm is the interior of the cell. All the organelles of the cell, the nucleus and various waste products are immersed in it.

The cytoplasm connects all parts of the cell with each other, numerous metabolic reactions take place in it. The cytoplasm is separated from the environment and divided into compartments by membranes, that is, cells have a membrane structure. It can be in two states - sol and gel. Sol- this is a semi-liquid, jelly-like state of the cytoplasm, in which vital processes proceed most intensively, and gel- a denser, gelatinous state that impedes the flow of chemical reactions and the transport of substances.

The liquid part of the cytoplasm without organelles is called hyaloplasm. Hyaloplasm, or cytosol, is a colloidal solution in which there is a kind of suspension of fairly large particles, such as proteins, surrounded by dipoles of water molecules. The sedimentation of this suspension does not occur due to the fact that they have the same charge and repel each other.

Organelles

Organelles- These are permanent components of the cell that perform certain functions.

Depending on the structural features, they are divided into membrane and non-membrane. Membrane organelles, in turn, are referred to as single-membrane (endoplasmic reticulum, Golgi complex and lysosomes) or double-membrane (mitochondria, plastids and nucleus). Non-membrane organelles are ribosomes, microtubules, microfilaments and the cell center. Of the listed organelles, only ribosomes are inherent in prokaryotes.

The structure and functions of the nucleus. Core- a large two-membrane organelle lying in the center of the cell or on its periphery. The size of the nucleus can vary within 3-35 microns. The shape of the nucleus is more often spherical or ellipsoid, but there are also rod-shaped, spindle-shaped, bean-shaped, lobed and even segmented nuclei. Some researchers believe that the shape of the nucleus corresponds to the shape of the cell itself.

Most cells have one nucleus, but, for example, in liver and heart cells there can be two, and in a number of neurons - up to 15. Skeletal muscle fibers usually contain many nuclei, but they are not cells in the full sense of the word, since they are formed in the result of the fusion of several cells.

The core is surrounded nuclear envelope, and its interior space is filled nuclear juice, or nucleoplasm (karyoplasm) in which are immersed chromatin And nucleolus. The nucleus performs such important functions as the storage and transmission of hereditary information, as well as the control of cell vital activity.

The role of the nucleus in the transmission of hereditary information has been convincingly proven in experiments with the green algae acetabularia. In a single giant cell, reaching a length of 5 cm, a hat, a leg and a rhizoid are distinguished. Moreover, it contains only one nucleus located in the rhizoid. In the 1930s, I. Hemmerling transplanted the nucleus of one species of acetabularia with a green color into a rhizoid of another species, with a brown color, in which the nucleus was removed. After some time, the plant with the transplanted nucleus grew a new hat, like an algae-donor of the nucleus. At the same time, the cap or stalk separated from the rhizoid, which did not contain a nucleus, died after some time.

nuclear envelope It is formed by two membranes - outer and inner, between which there is a space. The intermembrane space communicates with the cavity of the rough endoplasmic reticulum, and the outer membrane of the nucleus can carry ribosomes. The nuclear envelope is permeated with numerous pores, edged with special proteins. Substances are transported through the pores: the necessary proteins (including enzymes), ions, nucleotides and other substances enter the nucleus, and RNA molecules, waste proteins, subunits of ribosomes leave it. Thus, the functions of the nuclear envelope are the separation of the contents of the nucleus from the cytoplasm, as well as the regulation of the metabolism between the nucleus and the cytoplasm.

Nucleoplasm called the contents of the nucleus, in which the chromatin and nucleolus are immersed. It is a colloidal solution, chemically reminiscent of the cytoplasm. Enzymes of the nucleoplasm catalyze the exchange of amino acids, nucleotides, proteins, etc. The nucleoplasm is connected to the hyaloplasm through nuclear pores. The functions of the nucleoplasm, like the hyaloplasm, are to ensure the interconnection of all structural components of the nucleus and the implementation of a number of enzymatic reactions.

chromatin called a set of thin threads and granules immersed in the nucleoplasm. It can only be detected by staining, since the refractive indices of chromatin and nucleoplasm are approximately the same. The filamentous component of chromatin is called euchromatin, and granular heterochromatin. Euchromatin is weakly compacted, since hereditary information is read from it, while more spiralized heterochromatin is genetically inactive.

Chromatin is a structural modification of chromosomes in a non-dividing nucleus. Thus, chromosomes are constantly present in the nucleus; only their state changes depending on the function that the nucleus performs at the moment.

The composition of chromatin mainly includes nucleoproteins (deoxyribonucleoproteins and ribonucleoproteins), as well as enzymes, the most important of which are associated with the synthesis of nucleic acids, and some other substances.

The functions of chromatin consist, firstly, in the synthesis of nucleic acids specific to a given organism, which direct the synthesis of specific proteins, and secondly, in the transfer of hereditary properties from the mother cell to daughter cells, for which chromatin threads are packed into chromosomes during division.

nucleolus- a spherical body, clearly visible under a microscope, with a diameter of 1-3 microns. It is formed in chromatin regions that encode information about the structure of rRNA and ribosome proteins. The nucleolus in the nucleus is often one, but in those cells where intensive vital processes take place, there may be two or more nucleoli. The functions of the nucleoli are the synthesis of rRNA and the assembly of ribosome subunits by combining rRNA with proteins coming from the cytoplasm.

Mitochondria- two-membrane organelles of a round, oval or rod-shaped shape, although spiral-shaped ones are also found (in spermatozoa). Mitochondria are up to 1 µm in diameter and up to 7 µm in length. The space inside the mitochondria is filled with matrix. Matrix It is the main substance of mitochondria. A circular DNA molecule and ribosomes are immersed in it. The outer membrane of mitochondria is smooth and impermeable to many substances. The inner membrane has outgrowths - cristae, which increase the surface area of ​​membranes for chemical reactions to occur. On the surface of the membrane are numerous protein complexes that make up the so-called respiratory chain, as well as mushroom-shaped enzymes of ATP synthetase. In mitochondria, the aerobic stage of respiration takes place, during which ATP is synthesized.

plastids- large two-membrane organelles, characteristic only for plant cells. The inner space of plastids is filled stroma, or matrix. The stroma contains more or less advanced system membranous vesicles. thylakoids, which are collected in piles - grains, as well as its own circular DNA molecule and ribosomes. There are four main types of plastids: chloroplasts, chromoplasts, leucoplasts, and proplastids.

Chloroplasts- these are green plastids with a diameter of 3-10 microns, clearly visible under a microscope. They are found only in the green parts of plants - leaves, young stems, flowers and fruits. Chloroplasts are mostly oval or ellipsoid in shape, but can also be cup-shaped, spiral-shaped, and even lobed. The number of chloroplasts in a cell averages from 10 to 100 pieces. However, for example, in some algae it may be one, have a significant size and complex shape - then it is called chromatophore. In other cases, the number of chloroplasts can reach several hundred, while their size is small. The color of chloroplasts is due to the main pigment of photosynthesis - chlorophyll, although they contain additional pigments - carotenoids. Carotenoids become noticeable only in autumn, when the chlorophyll in aging leaves is destroyed. The main function of chloroplasts is photosynthesis. Light reactions of photosynthesis occur on thylakoid membranes, on which chlorophyll molecules are fixed, and dark reactions occur in the stroma, which contains numerous enzymes.

Chromoplasts are yellow, orange and red plastids containing carotenoid pigments. The shape of chromoplasts can also vary significantly: they are tubular, spherical, crystalline, etc. Chromoplasts give color to flowers and fruits of plants, attracting pollinators and dispersers of seeds and fruits.

Leucoplasts- These are white or colorless plastids, mostly round or oval in shape. They are common in non-photosynthetic parts of plants, such as leaf skin, potato tubers, etc. They store nutrients, most often starch, but in some plants it can be proteins or oil.

Plastids are formed in plant cells from proplastids, which are already present in the cells of the educational tissue and are small two-membrane bodies. On early stages development, different types of plastids are able to turn into each other: when exposed to light, the leukoplasts of a potato tuber and the chromoplasts of a carrot root turn green.

Plastids and mitochondria are called semi-autonomous cell organelles, since they have their own DNA molecules and ribosomes, carry out protein synthesis and divide independently of cell division. These features are explained by the origin from unicellular prokaryotic organisms. However, the "independence" of mitochondria and plastids is limited, since their DNA contains too few genes for free existence, while the rest of the information is encoded in the chromosomes of the nucleus, which allows it to control these organelles.

Endoplasmic reticulum (ER), or endoplasmic reticulum (ER), is a single-membrane organelle, which is a network of membrane cavities and tubules, occupying up to 30% of the contents of the cytoplasm. The diameter of ER tubules is about 25–30 nm. There are two types of EPS - rough and smooth. Rough XPS carries ribosomes and is where proteins are synthesized. Smooth EPS devoid of ribosomes. Its function is the synthesis of lipids and carbohydrates, as well as the transport, storage and disposal of toxic substances. It is especially developed in those cells where intensive metabolic processes take place, for example, in liver cells - hepatocytes - and skeletal muscle fibers. Substances synthesized in the EPS are transported to the Golgi apparatus. In the ER, cell membranes are also assembled, but their formation is completed in the Golgi apparatus.

golgi apparatus, or golgi complex, is a single-membrane organelle formed by a system of flat cisterns, tubules and vesicles laced off from them. The structural unit of the Golgi apparatus is dictyosome- a stack of tanks, on one pole of which substances from the ER come, and from the opposite pole, having undergone certain transformations, they are packed into bubbles and sent to other parts of the cell. The diameter of tanks is about 2 microns, and small bubbles are about 20-30 microns. The main functions of the Golgi complex are the synthesis of certain substances and the modification (change) of proteins, lipids and carbohydrates coming from the ER, the final formation of membranes, as well as the transport of substances through the cell, the renewal of its structures and the formation of lysosomes. The Golgi apparatus got its name in honor of the Italian scientist Camillo Golgi, who first discovered this organoid (1898).

Lysosomes- small single-membrane organelles up to 1 micron in diameter, which contain hydrolytic enzymes involved in intracellular digestion. The membranes of lysosomes are poorly permeable for these enzymes, so the performance of their functions by lysosomes is very accurate and targeted. So, they take an active part in the process of phagocytosis, forming digestive vacuoles, and in case of starvation or damage to certain parts of the cell, they digest them without affecting others. Recently, the role of lysosomes in cell death processes has been discovered.

Vacuole- a cavity in the cytoplasm of plant and animal cells, bounded by a membrane and filled with liquid. Digestive and contractile vacuoles are found in protozoan cells. The former take part in the process of phagocytosis, as they break down nutrients. The latter ensure the maintenance of water-salt balance due to osmoregulation. In multicellular animals, digestive vacuoles are mainly found.

In plant cells, vacuoles are always present, they are surrounded by a special membrane and filled with cell sap. The membrane surrounding the vacuole is similar in chemical composition, structure and functions to the plasma membrane. cell sap represents an aqueous solution of various inorganic and organic substances, including mineral salts, organic acids, carbohydrates, proteins, glycosides, alkaloids, etc. The vacuole can occupy up to 90% of the cell volume and push the nucleus to the periphery. This part of the cell performs storage, excretory, osmotic, protective, lysosomal and other functions, since it accumulates nutrients and waste products, it provides water supply and maintains the shape and volume of the cell, and also contains enzymes for the breakdown of many cell components. In addition, the biologically active substances of vacuoles can prevent many animals from eating these plants. In a number of plants, due to the swelling of vacuoles, cell growth occurs by stretching.

Vacuoles are also present in the cells of some fungi and bacteria, but in fungi they perform only the function of osmoregulation, while in cyanobacteria they maintain buoyancy and participate in the processes of nitrogen uptake from the air.

Ribosomes- small non-membrane organelles with a diameter of 15-20 microns, consisting of two subunits - large and small. Eukaryotic ribosome subunits are assembled in the nucleolus and then transported to the cytoplasm. The ribosomes of prokaryotes, mitochondria, and plastids are smaller than those of eukaryotes. Ribosome subunits include rRNA and proteins.

The number of ribosomes in a cell can reach several tens of millions: in the cytoplasm, mitochondria and plastids they are in a free state, and on the rough ER they are in a bound state. They take part in protein synthesis, in particular, they carry out the process of translation - the biosynthesis of a polypeptide chain on an mRNA molecule. On free ribosomes, proteins of hyaloplasm, mitochondria, plastids and own proteins of ribosomes are synthesized, while on ribosomes attached to the rough ER, proteins are translated for excretion from cells, assembly of membranes, formation of lysosomes and vacuoles.

Ribosomes can be located in the hyaloplasm singly or assembled in groups with simultaneous synthesis of several polypeptide chains on one mRNA. These groups of ribosomes are called polyribosomes, or polysomes.

microtubules- These are cylindrical hollow non-membrane organelles that penetrate the entire cytoplasm of the cell. Their diameter is about 25 nm, the wall thickness is 6-8 nm. They are made up of numerous protein molecules. tubulin, which first form 13 strands resembling beads and then assemble into a microtubule. Microtubules form a cytoplasmic reticulum that gives the cell shape and volume, connects the plasma membrane with other parts of the cell, provides transport of substances through the cell, takes part in the movement of the cell and intracellular components, as well as in the division of genetic material. They are part of the cell center and organelles of movement - flagella and cilia.

microfilaments, or microfilaments, are also non-membrane organelles, however, they have a filamentous shape and are formed not by tubulin, but actinome. They take part in the processes of membrane transport, intercellular recognition, division of the cell cytoplasm and in its movement. In muscle cells, the interaction of actin microfilaments with myosin filaments provides contraction.

Microtubules and microfilaments form the inner skeleton of the cell cytoskeleton. It is a complex network of fibers that provide mechanical support for the plasma membrane, determines the shape of the cell, the location of cellular organelles and their movement during cell division.

Cell Center- non-membrane organelle located in animal cells near the nucleus; it is absent in plant cells. Its length is about 0.2–0.3 µm, and its diameter is 0.1–0.15 µm. The cell center is made up of two centrioles lying in mutually perpendicular planes, And radiant sphere from microtubules. Each centriole is formed by nine groups of microtubules, collected in threes, i.e. triplets. The cell center takes part in the assembly of microtubules, the division of the hereditary material of the cell, as well as in the formation of flagella and cilia.

Organelles of movement. Flagella And cilia are outgrowths of cells covered with plasmalemma. These organelles are based on nine pairs of microtubules located along the periphery and two free microtubules in the center. Microtubules are interconnected by various proteins that ensure their coordinated deviation from the axis - oscillation. Fluctuations are energy-dependent, that is, the energy of macroergic bonds of ATP is spent on this process. Restoration of lost flagella and cilia is a function basal bodies, or kinetosomes located at their base.

The length of the cilia is about 10-15 nm, and the length of the flagella is 20-50 microns. Due to the strictly directed movements of the flagella and cilia, not only the movement of unicellular animals, spermatozoa, etc. is carried out, but also purification takes place. respiratory tract, the promotion of the egg through the fallopian tubes, since all these parts of the human body are lined with ciliated epithelium.

Inclusions

Inclusions- These are non-permanent components of the cell, which are formed and disappear in the course of its life. These include both reserve substances, for example, grains of starch or protein in plant cells, glycogen granules in animal and fungal cells, volutin in bacteria, fat drops in all cell types, and waste products, in particular, undigested food residues as a result of phagocytosis. , forming the so-called residual bodies.

The relationship of the structure and functions of the parts and organelles of the cell is the basis of its integrity

Each of the parts of the cell, on the one hand, is a separate structure with a specific structure and functions, and on the other hand, a component of a more complex system called a cell. Most of the hereditary information of a eukaryotic cell is concentrated in the nucleus, but the nucleus itself is not able to ensure its implementation, since this requires at least the cytoplasm, which acts as the main substance, and ribosomes, on which this synthesis occurs. Most ribosomes are located on the granular endoplasmic reticulum, from where proteins are most often transported to the Golgi complex, and then, after modification, to those parts of the cell for which they are intended, or are excreted. Membrane packaging of proteins and carbohydrates can be incorporated into organoid membranes and the cytoplasmic membrane, ensuring their constant renewal. Lysosomes and vacuoles, which perform the most important functions, are also laced from the Golgi complex. For example, without lysosomes, cells would quickly turn into a kind of dump of waste molecules and structures.

All of these processes require energy produced by mitochondria and, in plants, also by chloroplasts. And although these organelles are relatively autonomous, since they have their own DNA molecules, some of their proteins are still encoded by the nuclear genome and synthesized in the cytoplasm.

Thus, the cell is an inseparable unity of its constituent components, each of which performs its own unique function.

Metabolism and energy conversion are properties of living organisms. Energy and plastic metabolism, their relationship. Stages of energy metabolism. Fermentation and respiration. Photosynthesis, its significance, cosmic role. Phases of photosynthesis. Light and dark reactions of photosynthesis, their relationship. Chemosynthesis. The role of chemosynthetic bacteria on Earth

Metabolism and energy conversion - properties of living organisms

The cell can be likened to a miniature chemical factory where hundreds and thousands of chemical reactions take place.

Metabolism- a set of chemical transformations aimed at the preservation and self-reproduction of biological systems.

It includes the intake of substances into the body during nutrition and respiration, intracellular metabolism, or metabolism, as well as the allocation of end products of metabolism.

Metabolism is inextricably linked with the processes of converting one type of energy into another. For example, in the process of photosynthesis, light energy is stored in the form of the energy of chemical bonds of complex organic molecules, and in the process of respiration it is released and spent on the synthesis of new molecules, mechanical and osmotic work, is dissipated in the form of heat, etc.

The flow of chemical reactions in living organisms is ensured by biological catalysts of protein nature - enzymes, or enzymes. Like other catalysts, enzymes accelerate the flow of chemical reactions in the cell by tens and hundreds of thousands of times, and sometimes even make them possible, but do not change either the nature or properties of the final product (products) of the reaction and do not change themselves. Enzymes can be both simple and complex proteins, which, in addition to the protein part, also include a non-protein part - cofactor (coenzyme). Examples of enzymes are salivary amylase, which breaks down polysaccharides during prolonged chewing, and pepsin, which ensures the digestion of proteins in the stomach.

Enzymes differ from non-protein catalysts in their high specificity of action, a significant increase in the reaction rate with their help, as well as the ability to regulate the action by changing the reaction conditions or interacting with various substances. In addition, the conditions under which enzymatic catalysis proceeds differ significantly from those under which non-enzymatic catalysis occurs: the optimum temperature for the functioning of enzymes in the human body is $37°C$, the pressure should be close to atmospheric, and the $pH$ of the medium can significantly hesitate. So, for amylase, an alkaline environment is necessary, and for pepsin, an acidic one.

The mechanism of action of enzymes is to reduce the activation energy of substances (substrates) that enter into the reaction due to the formation of intermediate enzyme-substrate complexes.

Energy and plastic metabolism, their relationship

Metabolism consists of two processes simultaneously occurring in the cell: plastic and energy exchanges.

Plastic metabolism (anabolism, assimilation) is a set of synthesis reactions that go with the expenditure of ATP energy. In the process of plastic metabolism, organic substances are synthesized, needed by the cell. Examples of plastic exchange reactions are photosynthesis, protein biosynthesis, and DNA replication (self-doubling).

Energy metabolism (catabolism, dissimilation) is a set of reactions that break down complex substances into simpler ones. As a result of energy metabolism, energy is released, stored in the form of ATP. The most important processes of energy metabolism are respiration and fermentation.

Plastic and energy exchanges are inextricably linked, since in the process of plastic exchange organic substances are synthesized and this requires the energy of ATP, and in the process of energy metabolism organic substances are split and energy is released, which will then be spent on synthesis processes.

Organisms receive energy in the process of nutrition, and release it and convert it into an accessible form mainly in the process of respiration. According to the way of nutrition, all organisms are divided into autotrophs and heterotrophs. Autotrophs able to independently synthesize organic substances from inorganic, and heterotrophs use exclusively ready-made organic substances.

Stages of energy metabolism

Despite the complexity of energy metabolism reactions, it is conditionally divided into three stages: preparatory, anaerobic (oxygen-free) and aerobic (oxygen).

On preparatory stage molecules of polysaccharides, lipids, proteins, nucleic acids break down into simpler ones, for example, glucose, glycerol and fatty acids, amino acids, nucleotides, etc. This stage can take place directly in the cells or in the intestine, from where the split substances are delivered with blood flow.

anaerobic stage energy metabolism is accompanied by further splitting of the monomers of organic compounds to even simpler intermediate products, for example, pyruvic acid, or pyruvate. It does not require the presence of oxygen, and for many organisms living in the silt of swamps or in the human intestine, it is the only way to obtain energy. The anaerobic stage of energy metabolism takes place in the cytoplasm.

Various substances can undergo oxygen-free cleavage, but glucose is often the substrate of the reactions. The process of its oxygen-free splitting is called glycolysis. During glycolysis, the glucose molecule loses four hydrogen atoms, i.e., it is oxidized, and two molecules of pyruvic acid, two ATP molecules and two molecules of the reduced hydrogen carrier $NADH + H^(+)$ are formed:

$C_6H_(12)O_6 + 2H_3PO_4 + 2ADP + 2NAD → 2C_3H_4O_3 + 2ATP + 2NADH + H^(+) + 2H_2O$.

The formation of ATP from ADP occurs due to the direct transfer of a phosphate anion from a previously phosphorylated sugar and is called substrate phosphorylation.

Aerobic stage energy exchange can occur only in the presence of oxygen, while the intermediate compounds formed in the process of oxygen-free cleavage are oxidized to final products (carbon dioxide and water) and most of the energy stored in the chemical bonds of organic compounds is released. It passes into the energy of macroergic bonds of 36 ATP molecules. This stage is also called tissue respiration. In the absence of oxygen, intermediate compounds are converted into other organic substances, a process called fermentation.

Breath

The mechanism of cellular respiration is schematically shown in fig.

Aerobic respiration occurs in mitochondria, while pyruvic acid first loses one carbon atom, which is accompanied by the synthesis of one reducing equivalent of $NADH + H^(+)$ and an acetyl coenzyme A (acetyl-CoA) molecule:

$C_3H_4O_3 + NAD + H~CoA → CH_3CO~CoA + NADH + H^(+) + CO_2$.

Acetyl-CoA in the mitochondrial matrix is ​​involved in a chain of chemical reactions, the totality of which is called Krebs cycle (tricarboxylic acid cycle, citric acid cycle). During these transformations, two ATP molecules are formed, acetyl-CoA is completely oxidized to carbon dioxide, and its hydrogen ions and electrons are attached to the hydrogen carriers $NADH + H^(+)$ and $FADH_2$. Carriers transport hydrogen protons and electrons to the inner membranes of mitochondria, which form cristae. With the help of carrier proteins, hydrogen protons are injected into the intermembrane space, and electrons are transferred along the so-called respiratory chain enzymes located on the inner membrane of mitochondria and are dumped on oxygen atoms:

$O_2+2e^(-)→O_2^-$.

It should be noted that some proteins of the respiratory chain contain iron and sulfur.

From the intermembrane space, hydrogen protons are transported back to the mitochondrial matrix with the help of special enzymes - ATP synthases, and the energy released in this case is spent on the synthesis of 34 ATP molecules from each glucose molecule. This process is called oxidative phosphorylation. In the mitochondrial matrix, hydrogen protons react with oxygen radicals to form water:

$4H^(+)+O_2^-→2H_2O$.

The set of reactions of oxygen respiration can be expressed as follows:

$2C_3H_4O_3 + 6O_2 + 36H_3PO_4 + 36ADP → 6CO_2 + 38H_2O + 36ATP.$

The overall breathing equation looks like this:

$C_6H_(12)O_6 + 6O_2 + 38H_3PO_4 + 38ADP → 6CO_2 + 40H_2O + 38ATP.$

Fermentation

In the absence of oxygen or its deficiency, fermentation occurs. Fermentation is an evolutionarily earlier way of obtaining energy than respiration, but it is energetically less profitable, since fermentation produces organic substances that are still rich in energy. There are several main types of fermentation: lactic acid, alcohol, acetic acid, etc. So, in skeletal muscles in the absence of oxygen during fermentation, pyruvic acid is reduced to lactic acid, while the previously formed reducing equivalents are consumed, and only two ATP molecules remain:

$2C_3H_4O_3 + 2NADH + H^(+) → 2C_3H_6O_3 + 2NAD$.

During fermentation with the help of yeast fungi, pyruvic acid in the presence of oxygen turns into ethyl alcohol and carbon monoxide (IV):

$C_3H_4O_3 + NADH + H^(+) → C_2H_5OH + CO_2 + NAD^(+)$.

During fermentation with the help of microorganisms, pyruvic acid can also form acetic, butyric, formic acids, etc.

ATP obtained as a result of energy metabolism is consumed in the cell for various types of work: chemical, osmotic, electrical, mechanical and regulatory. Chemical work consists in the biosynthesis of proteins, lipids, carbohydrates, nucleic acids and other vital compounds. Osmotic work includes the processes of absorption by the cell and removal from it of substances that are in the extracellular space in concentrations greater than in the cell itself. Electrical work is closely related to osmotic work, since it is as a result of the movement of charged particles through the membranes that the charge of the membrane is formed and the properties of excitability and conductivity are acquired. mechanical work associated with the movement of substances and structures within the cell, as well as the cell as a whole. Regulatory work includes all processes aimed at coordinating processes in the cell.

Photosynthesis, its significance, cosmic role

photosynthesis called the process of converting light energy into the energy of chemical bonds of organic compounds with the participation of chlorophyll.

As a result of photosynthesis, about 150 billion tons of organic matter and approximately 200 billion tons of oxygen are produced annually. This process ensures the circulation of carbon in the biosphere, preventing the accumulation of carbon dioxide and thereby preventing the occurrence of the greenhouse effect and overheating of the Earth. The organic substances formed as a result of photosynthesis are not completely consumed by other organisms, a significant part of them formed mineral deposits (hard and brown coal, oil) over millions of years. IN Lately rapeseed oil (“biodiesel”) and alcohol obtained from plant residues also began to be used as fuel. From oxygen, under the action of electrical discharges, ozone is formed, which forms an ozone shield that protects all life on Earth from the harmful effects of ultraviolet rays.

Our compatriot, the outstanding plant physiologist K. A. Timiryazev (1843-1920) called the role of photosynthesis “cosmic”, since it connects the Earth with the Sun (space), providing an influx of energy to the planet.

Phases of photosynthesis. Light and dark reactions of photosynthesis, their relationship

In 1905, the English plant physiologist F. Blackman discovered that the rate of photosynthesis cannot increase indefinitely, some factor limits it. Based on this, he proposed the existence of two phases of photosynthesis: light And dark. At low light intensity, the speed of light reactions increases in proportion to the increase in light intensity, and, in addition, these reactions do not depend on temperature, since enzymes are not needed for their occurrence. Light reactions occur on thylakoid membranes.

The rate of dark reactions, on the contrary, increases with increasing temperature; however, upon reaching the temperature threshold of $30°C$, this growth stops, which indicates the enzymatic nature of these transformations occurring in the stroma. It should be noted that light also has a certain effect on dark reactions, despite the fact that they are called dark.

The light phase of photosynthesis proceeds on thylakoid membranes, which carry several types of protein complexes, the main of which are photosystems I and II, as well as ATP synthase. The composition of photosystems includes pigment complexes, in which, in addition to chlorophyll, there are also carotenoids. Carotenoids trap light in those regions of the spectrum in which chlorophyll does not, and also protect chlorophyll from destruction by high-intensity light.

In addition to pigment complexes, photosystems also include a number of electron acceptor proteins that successively transfer electrons from chlorophyll molecules to each other. The sequence of these proteins is called chloroplast electron transport chain.

A special complex of proteins is also associated with photosystem II, which ensures the release of oxygen during photosynthesis. This oxygen-evolving complex contains manganese and chlorine ions.

IN light phase light quanta, or photons, falling on chlorophyll molecules located on thylakoid membranes, transfer them to an excited state, characterized by more high energy electrons. At the same time, excited electrons from the chlorophyll of photosystem I are transferred through a chain of intermediaries to the hydrogen carrier NADP, which adds hydrogen protons, which are always present in an aqueous solution:

$NADP + 2e^(-) + 2H^(+) → NADPH + H^(+)$.

The reduced $NADPH + H^(+)$ will subsequently be used in the dark stage. Electrons from the chlorophyll of photosystem II are also transferred along the electron transport chain, but they fill the "electron holes" of the chlorophyll of photosystem I. The lack of electrons in the chlorophyll of photosystem II is filled by depriving water molecules from water molecules, which occurs with the participation of the oxygen-releasing complex already mentioned above. As a result of the decomposition of water molecules, which is called photolysis, hydrogen protons are formed and molecular oxygen is released, which is a by-product of photosynthesis:

$H_2O → 2H^(+) + 2e^(-) + (1)/(2)O_2$.

Genetic information in a cell. Genes, genetic code and its properties. Matrix nature of biosynthetic reactions. Biosynthesis of protein and nucleic acids

Genetic information in a cell

Reproduction of one's own kind is one of the fundamental properties of the living. Due to this phenomenon, there is a similarity not only between organisms, but also between individual cells, as well as their organelles (mitochondria and plastids). The material basis of this similarity is the transfer of DNA encrypted in the sequence of nucleotides genetic information, which is carried out due to the processes of replication (self-doubling) of DNA. All features and properties of cells and organisms are realized thanks to proteins, the structure of which is primarily determined by the DNA nucleotide sequences. Therefore, it is the biosynthesis of nucleic acids and proteins that is of paramount importance in metabolic processes. The structural unit of hereditary information is the gene.

Genes, genetic code and its properties

Hereditary information in a cell is not monolithic, it is divided into separate "words" - genes.

Gene is the basic unit of genetic information.

The work on the "Human Genome" program, which was carried out simultaneously in several countries and was completed at the beginning of this century, gave us an understanding that a person has only about 25-30 thousand genes, but information from most of our DNA is never read, since it contains a huge number of meaningless sections, repeats and genes encoding features that have lost their meaning for humans (tail, body hair, etc.). In addition, a number of genes responsible for the development of hereditary diseases, as well as drug target genes, have been deciphered. However practical use the results obtained during the implementation of this program are postponed until the genomes of more people are deciphered and it becomes clear how they differ.

Genes encoding the primary structure of a protein, ribosomal or transfer RNA are called structural, and genes that provide activation or suppression of reading information from structural genes - regulatory. However, even structural genes contain regulatory regions.

The hereditary information of organisms is encrypted in DNA in the form of certain combinations of nucleotides and their sequence - genetic code. Its properties are: triplet, specificity, universality, redundancy and non-overlapping. In addition, there are no punctuation marks in the genetic code.

Each amino acid is encoded in DNA by three nucleotides. triplet for example, methionine is encoded by the TAC triplet, that is, the triplet code. On the other hand, each triplet encodes only one amino acid, which is its specificity or unambiguity. The genetic code is universal for all living organisms, that is, hereditary information about human proteins can be read by bacteria and vice versa. This testifies to the unity of the origin of the organic world. However, 64 combinations of three nucleotides correspond to only 20 amino acids, as a result of which 2-6 triplets can encode one amino acid, that is, the genetic code is redundant, or degenerate. Three triplets do not have corresponding amino acids, they are called stop codons, as they mark the end of the synthesis of the polypeptide chain.

The sequence of bases in DNA triplets and the amino acids they encode

*Stop codon, indicating the end of the synthesis of the polypeptide chain.

Abbreviations for amino acid names:

Ala - alanine

Arg - arginine

Asn - asparagine

Asp - aspartic acid

Val - valine

His - histidine

Gly - glycine

Gln - glutamine

Glu - glutamic acid

Ile - isoleucine

Leu - leucine

Liz - lysine

Meth - methionine

Pro - proline

Ser - serine

Tyr - tyrosine

Tre - threonine

Three - tryptophan

Fen - phenylalanine

cis - cysteine

If you start reading genetic information not from the first nucleotide in the triplet, but from the second, then not only will the reading frame shift, the protein synthesized in this way will be completely different not only in the nucleotide sequence, but also in structure and properties. There are no punctuation marks between the triplets, so there are no obstacles to the shift of the reading frame, which opens up scope for the occurrence and maintenance of mutations.

Matrix nature of biosynthetic reactions

Bacterial cells are able to duplicate every 20-30 minutes, and eukaryotic cells - every day and even more often, which requires high speed and accuracy of DNA replication. In addition, each cell contains hundreds and thousands of copies of many proteins, especially enzymes, therefore, for their reproduction, the "piece" method of their production is unacceptable. A more progressive way is stamping, which allows you to get numerous exact copies of the product and also reduce its cost. For stamping, a matrix is ​​needed, with which an impression is made.

In cells, the principle of matrix synthesis is that new molecules of proteins and nucleic acids are synthesized in accordance with the program laid down in the structure of pre-existing molecules of the same nucleic acids (DNA or RNA).

Biosynthesis of protein and nucleic acids

DNA replication. DNA is a double-stranded biopolymer whose monomers are nucleotides. If DNA biosynthesis proceeded according to the principle of photocopying, then numerous distortions and errors in hereditary information would inevitably arise, which would ultimately lead to the death of new organisms. Therefore, the process of DNA duplication is different, in a semi-conservative way: the DNA molecule unwinds, and on each of the chains a new chain is synthesized according to the principle of complementarity. The process of self-reproduction of the DNA molecule, which ensures the exact copying of hereditary information and its transmission from generation to generation, is called replication(from lat. replication- repetition). As a result of replication, two absolutely exact copies of the parent DNA molecule are formed, each of which carries one copy of the parent.

The process of replication is actually extremely complex, since a number of proteins are involved in it. Some of them unwind the double helix of DNA, others break the hydrogen bonds between the nucleotides of complementary chains, others (for example, the DNA polymerase enzyme) select new nucleotides according to the principle of complementarity, etc. The two DNA molecules formed as a result of replication diverge in two during division. newly formed daughter cells.

Errors in the replication process are extremely rare, but if they do occur, they are very quickly eliminated by both DNA polymerases and special repair enzymes, since any error in the nucleotide sequence can lead to an irreversible change in the structure and functions of the protein and, ultimately, adversely affect the viability of a new cell or even an individual.

protein biosynthesis. As the outstanding philosopher of the 19th century F. Engels figuratively put it: "Life is a form of existence of protein bodies." The structure and properties of protein molecules are determined by their primary structure, i.e., the sequence of amino acids encoded in DNA. Not only the existence of the polypeptide itself, but also the functioning of the cell as a whole depends on the accuracy of reproduction of this information; therefore, the process of protein synthesis is of great importance. It seems to be the most complex process of synthesis in the cell, since up to three hundred different enzymes and other macromolecules are involved here. In addition, it flows at a high speed, which requires even greater precision.

There are two main steps in protein biosynthesis: transcription and translation.

Transcription(from lat. transcription- rewriting) is the biosynthesis of mRNA molecules on a DNA template.

Since the DNA molecule contains two antiparallel chains, reading information from both chains would lead to the formation of completely different mRNAs, therefore their biosynthesis is possible only on one of the chains, which is called coding, or codogenic, in contrast to the second, non-coding, or non-codogenic. The rewriting process is provided by a special enzyme, RNA polymerase, which selects RNA nucleotides according to the principle of complementarity. This process can take place both in the nucleus and in organelles that have their own DNA - mitochondria and plastids.

The mRNA molecules synthesized during transcription undergo a complex process of preparation for translation (mitochondrial and plastid mRNAs can remain inside organelles, where the second stage of protein biosynthesis takes place). In the process of mRNA maturation, the first three nucleotides (AUG) and a tail of adenyl nucleotides are attached to it, the length of which determines how many protein copies can be synthesized on a given molecule. Only then do mature mRNAs leave the nucleus through nuclear pores.

In parallel, the process of amino acid activation occurs in the cytoplasm, during which the amino acid is attached to the corresponding free tRNA. This process is catalyzed by a special enzyme, it consumes ATP.

Broadcast(from lat. broadcast- transfer) is the biosynthesis of a polypeptide chain on an mRNA template, in which genetic information is translated into a sequence of amino acids of the polypeptide chain.

The second stage of protein synthesis most often occurs in the cytoplasm, for example, on the rough endoplasmic reticulum. Its occurrence requires the presence of ribosomes, activation of tRNA, during which they attach the corresponding amino acids, the presence of Mg2+ ions, as well as optimal environmental conditions (temperature, pH, pressure, etc.).

To start broadcasting initiation) a small subunit of the ribosome is attached to the mRNA molecule ready for synthesis, and then, according to the principle of complementarity, the tRNA carrying the amino acid methionine is selected to the first codon (AUG). Only then does the large subunit of the ribosome join. Within the assembled ribosome, there are two mRNA codons, the first of which is already occupied. A second tRNA, also carrying an amino acid, is attached to the codon adjacent to it, after which a peptide bond is formed between the amino acid residues with the help of enzymes. The ribosome moves one codon of the mRNA; the first of the tRNA, freed from the amino acid, returns to the cytoplasm for the next amino acid, and a fragment of the future polypeptide chain, as it were, hangs on the remaining tRNA. The next tRNA joins the new codon, which is within the ribosome, the process repeats and step by step the polypeptide chain lengthens, i.e., it elongation.

End of protein synthesis termination) occurs as soon as a specific nucleotide sequence is encountered in an mRNA molecule that does not encode an amino acid (stop codon). After that, the ribosome, mRNA and polypeptide chain are separated, and the newly synthesized protein acquires the appropriate structure and is transported to the part of the cell where it will perform its functions.

Translation is a very energy-intensive process, since the energy of one ATP molecule is spent on attaching one amino acid to tRNA, and several more are used to move the ribosome along the mRNA molecule.

To accelerate the synthesis of certain protein molecules, several ribosomes can be sequentially attached to the mRNA molecule, which form a single structure - polysome.

The cell is the genetic unit of living things. Chromosomes, their structure (shape and size) and functions. The number of chromosomes and their species constancy. Somatic and sex cells. Cell life cycle: interphase and mitosis. Mitosis is the division of somatic cells. Meiosis. Phases of mitosis and meiosis. The development of germ cells in plants and animals. Cell division is the basis for the growth, development and reproduction of organisms. The role of meiosis and mitosis

The cell is the genetic unit of life

Despite the fact that nucleic acids are the carrier of genetic information, the implementation of this information is impossible outside the cell, which is easily proved by the example of viruses. These organisms, often containing only DNA or RNA, cannot reproduce on their own, for this they must use the hereditary apparatus of the cell. They cannot even penetrate the cell without the help of the cell itself, except by using the mechanisms of membrane transport or due to cell damage. Most viruses are unstable, they die after a few hours of exposure to the open air. Therefore, the cell is a genetic unit of the living, which has a minimum set of components for the preservation, modification and implementation of hereditary information, as well as its transmission to descendants.

Most of the genetic information of a eukaryotic cell is located in the nucleus. A feature of its organization is that, unlike the DNA of a prokaryotic cell, eukaryotic DNA molecules are not closed and form complex complexes with proteins - chromosomes.

Chromosomes, their structure (shape and size) and functions

Chromosome(from Greek. chrome- color, color and catfish body) is a structure cell nucleus, which contains genes and carries certain hereditary information about the signs and properties of the organism.

Sometimes the ring DNA molecules of prokaryotes are also called chromosomes. Chromosomes are capable of self-duplication, they have structural and functional individuality and retain it in a number of generations. Each cell carries all the hereditary information of the body, but only a small part of it works.

The basis of the chromosome is a double-stranded DNA molecule packed with proteins. In eukaryotes, histone and non-histone proteins interact with DNA, while in prokaryotes, histone proteins are absent.

Chromosomes are best seen under a light microscope during cell division, when, as a result of compaction, they take the form of rod-shaped bodies separated by a primary constriction - centromere — on shoulders. The chromosome may also have secondary constriction, which in some cases separates the so-called satellite. The ends of chromosomes are called telomeres. Telomeres prevent the ends of chromosomes from sticking together and ensure their attachment to the nuclear membrane in a non-dividing cell. At the beginning of division, the chromosomes are doubled and consist of two daughter chromosomes - chromatids attached at the centromere.

According to the shape, equal-arm, unequal-arm and rod-shaped chromosomes are distinguished. Chromosome sizes vary significantly, but the average chromosome has a size of 5 $×$ 1.4 µm.

In some cases, chromosomes, as a result of numerous DNA duplications, contain hundreds and thousands of chromatids: such giant chromosomes are called polythene. They are found in the salivary glands of Drosophila larvae, as well as in the digestive glands of roundworms.

The number of chromosomes and their species constancy. Somatic and sex cells

According to the cellular theory, a cell is a unit of structure, life and development of an organism. Thus, such important functions of living things as growth, reproduction and development of the organism are provided at the cellular level. Cells of multicellular organisms can be divided into somatic and sex.

somatic cells are all the cells of the body that are formed as a result of mitotic division.

The study of chromosomes made it possible to establish that the somatic cells of the organism of each biological species are characterized by a constant number of chromosomes. For example, a person has 46 of them. The set of chromosomes of somatic cells is called diploid(2n), or double.

sex cells, or gametes, are specialized cells that serve for sexual reproduction.

Gametes always contain half as many chromosomes as in somatic cells (in humans - 23), so the set of chromosomes of germ cells is called haploid(n), or single. Its formation is associated with meiotic cell division.

The amount of DNA of somatic cells is designated as 2c, and that of germ cells is 1c. The genetic formula of somatic cells is written as 2n2c, and sex - 1n1c.

In the nuclei of some somatic cells, the number of chromosomes may differ from their number in somatic cells. If this difference is greater by one, two, three, etc. haploid sets, then such cells are called polyploid(tri-, tetra-, pentaploid, respectively). In such cells, metabolic processes are usually very intensive.

The number of chromosomes in itself is not a species-specific trait, since different organisms may have the same number of chromosomes, while related ones may have different numbers. For example, malarial plasmodium and horse roundworm have two chromosomes, while humans and chimpanzees have 46 and 48, respectively.

Human chromosomes are divided into two groups: autosomes and sex chromosomes (heterochromosomes). Autosome there are 22 pairs in human somatic cells, they are the same for men and women, and sex chromosomes only one pair, but it is she who determines the sex of the individual. There are two types of sex chromosomes - X and Y. The cells of the body of a woman carry two X chromosomes, and men - X and Y.

Karyotype- this is a set of signs of the chromosome set of an organism (the number of chromosomes, their shape and size).

The conditional record of the karyotype includes the total number of chromosomes, sex chromosomes, and possible deviations in the set of chromosomes. For example, the karyotype of a normal male is written as 46,XY, while the karyotype of a normal woman is 46,XX.

Cell life cycle: interphase and mitosis

Cells do not arise each time anew, they are formed only as a result of the division of mother cells. After separation, the daughter cells take some time to form organelles and acquire the appropriate structure that would ensure the performance of a certain function. This period of time is called ripening.

The period of time from the appearance of a cell as a result of division to its division or death is called cell life cycle.

In eukaryotic cells, the life cycle is divided into two main stages: interphase and mitosis.

Interphase- this is the period of time in the life cycle in which the cell does not divide and functions normally. The interphase is divided into three periods: G 1 -, S- and G 2 -periods.

G 1 -period(presynthetic, postmitotic) is a period of cell growth and development, during which there is an active synthesis of RNA, proteins and other substances necessary for the complete life support of the newly formed cell. By the end of this period, the cell may begin to prepare for DNA duplication.

IN S-period(synthetic) the process of DNA replication takes place. The only part of the chromosome that does not undergo replication is the centromere, therefore, the resulting DNA molecules do not completely diverge, but remain fastened in it, and at the beginning of division, the chromosome has an X-shaped appearance. The genetic formula of the cell after DNA duplication is 2n4c. Also in the S-period, doubling of the centrioles of the cell center occurs.

G 2 -period(postsynthetic, premitotic) is characterized by intensive synthesis of RNA, proteins and ATP necessary for the process of cell division, as well as the separation of centrioles, mitochondria and plastids. Until the end of the interphase, the chromatin and nucleolus remain clearly distinguishable, the integrity of the nuclear membrane is not disturbed, and the organelles do not change.

Some of the cells of the body are able to perform their functions throughout the life of the body (neurons of our brain, muscle cells of the heart), while others exist for a short time, after which they die (cells of the intestinal epithelium, cells of the epidermis of the skin). Consequently, the processes of cell division and the formation of new cells must constantly occur in the body, which would replace the dead ones. Cells capable of dividing are called stem. In the human body, they are found in the red bone marrow, in the deep layers of the epidermis of the skin and other places. Using these cells, you can grow a new organ, achieve rejuvenation, and also clone the body. The prospects for the use of stem cells are quite clear, but the moral and ethical aspects of this problem are still being discussed, since in most cases embryonic stem cells obtained from human fetuses killed during abortion are used.

The duration of interphase in plant and animal cells averages 10-20 hours, while mitosis takes about 1-2 hours.

In the course of successive divisions in multicellular organisms, daughter cells become more and more diverse, as they read information from an increasing number of genes.

Some cells eventually stop dividing and die, which may be due to the completion of certain functions, as in the case of epidermal cells of the skin and blood cells, or to damage to these cells by environmental factors, in particular pathogens. Genetically programmed cell death is called apoptosis while accidental death is necrosis.

Mitosis is the division of somatic cells. Phases of mitosis

Mitosis- a method of indirect division of somatic cells.

During mitosis, the cell goes through a series of successive phases, as a result of which each daughter cell receives the same set of chromosomes as in the mother cell.

Mitosis is divided into four main phases: prophase, metaphase, anaphase, and telophase. Prophase- the longest stage of mitosis, during which chromatin condensation occurs, as a result of which X-shaped chromosomes, consisting of two chromatids (daughter chromosomes), become visible. In this case, the nucleolus disappears, the centrioles diverge towards the poles of the cell, and the achromatin spindle (spindle) of microtubules begins to form. At the end of prophase, the nuclear membrane breaks up into separate vesicles.

IN metaphase chromosomes line up along the equator of the cell with their centromeres, to which microtubules of a fully formed division spindle are attached. At this stage of division, the chromosomes are most dense and have a characteristic shape, which makes it possible to study the karyotype.

IN anaphase rapid DNA replication occurs in the centromeres, as a result of which the chromosomes split and the chromatids diverge towards the poles of the cell, stretched by microtubules. The distribution of chromatids must be absolutely equal, since it is this process that maintains the constancy of the number of chromosomes in the cells of the body.

On the stage telophase daughter chromosomes gather at the poles, despiralize, around them nuclear envelopes form from the vesicles, and nucleoli appear in the newly formed nuclei.

After the division of the nucleus, the division of the cytoplasm occurs - cytokinesis, during which there is a more or less uniform distribution of all the organelles of the mother cell.

Thus, as a result of mitosis, two daughter cells are formed from one mother cell, each of which is a genetic copy of the mother cell (2n2c).

In diseased, damaged, aging cells and specialized tissues of the body, a slightly different division process can occur - amitosis. Amitosis called direct division of eukaryotic cells, in which the formation of genetically equivalent cells does not occur, since the cellular components are distributed unevenly. It occurs in plants in the endosperm and in animals in the liver, cartilage, and cornea of ​​the eye.

Meiosis. Phases of meiosis

Meiosis- this is a method of indirect division of primary germ cells (2n2c), as a result of which haploid cells (1n1c), most often germ cells, are formed.

Unlike mitosis, meiosis consists of two successive cell divisions, each preceded by an interphase. The first division of meiosis (meiosis I) is called reduction, since in this case the number of chromosomes is halved, and the second division (meiosis II) - equational, since in its process the number of chromosomes is conserved.

Interphase I proceeds similarly to the interphase of mitosis. Meiosis I is divided into four phases: prophase I, metaphase I, anaphase I and telophase I. prophase I Two major processes occur: conjugation and crossing over. Conjugation- this is the process of fusion of homologous (paired) chromosomes along the entire length. The pairs of chromosomes formed during conjugation are retained until the end of metaphase I.

Crossing over- mutual exchange of homologous regions of homologous chromosomes. As a result of crossing over, the chromosomes received by the organism from both parents acquire new combinations of genes, which leads to the appearance of genetically diverse offspring. At the end of prophase I, as in the prophase of mitosis, the nucleolus disappears, the centrioles diverge towards the poles of the cell, and the nuclear envelope disintegrates.

IN metaphase I pairs of chromosomes line up along the equator of the cell, microtubules of the fission spindle are attached to their centromeres.

IN anaphase I whole homologous chromosomes consisting of two chromatids diverge to the poles.

IN telophase I around clusters of chromosomes at the poles of the cell, nuclear membranes form, nucleoli form.

Cytokinesis I provides division of cytoplasms of daughter cells.

The daughter cells formed as a result of meiosis I (1n2c) are genetically heterogeneous, since their chromosomes, randomly dispersed to the poles of the cell, contain unequal genes.

Comparative characteristics of mitosis and meiosis

sign	Mitosis	Meiosis
What cells start dividing?	Somatic (2n)	Primary germ cells (2n)
Number of divisions	1	2
How many and what kind of cells are formed in the process of division?	2 somatic (2n)	4 sexual (n)
Interphase		Cell preparation for division, DNA duplication	Very short, DNA duplication does not occur
Phases		Meiosis I	Meiosis II
Prophase		Chromosome condensation, disappearance of the nucleolus, disintegration of the nuclear envelope, conjugation and crossing over may occur	Condensation of chromosomes, disappearance of the nucleolus, disintegration of the nuclear envelope
metaphase		Pairs of chromosomes are located along the equator, a division spindle is formed	Chromosomes line up along the equator, the spindle of division is formed
Anaphase		Homologous chromosomes from two chromatids diverge towards the poles	Chromatids diverge towards the poles
Telophase		Chromosomes despiralize, new nuclear envelopes and nucleoli form	Chromosomes despiralize, new nuclear envelopes and nucleoli form

Interphase II very short, since DNA doubling does not occur in it, that is, there is no S-period.

Meiosis II also divided into four phases: prophase II, metaphase II, anaphase II and telophase II. IN prophase II the same processes occur as in prophase I, with the exception of conjugation and crossing over.

IN metaphase II Chromosomes are located along the equator of the cell.

IN anaphase II Chromosomes split at the centromere and the chromatids stretch towards the poles.

IN telophase II nuclear membranes and nucleoli form around clusters of daughter chromosomes.

After cytokinesis II the genetic formula of all four daughter cells is 1n1c, but they all have a different set of genes, which is the result of crossing over and a random combination of maternal and paternal chromosomes in daughter cells.

The development of germ cells in plants and animals

Gametogenesis(from Greek. gamete- wife, gametes- husband and genesis- origin, occurrence) is the process of formation of mature germ cells.

Since sexual reproduction most often requires two individuals - female and male, producing different sex cells - eggs and sperm, then the processes of formation of these gametes should be different.

The nature of the process also depends to a large extent on whether it occurs in a plant or animal cell, since in plants only mitosis occurs during the formation of gametes, while in animals both mitosis and meiosis occur.

The development of germ cells in plants. In angiosperms, the formation of male and female germ cells occurs in different parts of the flower - stamens and pistils, respectively.

Before the formation of male germ cells - microgametogenesis(from Greek. micros- small) - happening microsporogenesis, that is, the formation of microspores in the anthers of the stamens. This process is associated with the meiotic division of the mother cell, which results in four haploid microspores. Microgametogenesis is associated with mitotic division microspores, giving a male gametophyte of two cells - a large vegetative(siphonogenic) and shallow generative. After division, the male gametophyte is covered with dense shells and forms a pollen grain. In some cases, even in the process of pollen maturation, and sometimes only after transfer to the stigma of the pistil, the generative cell divides mitotically with the formation of two immobile male germ cells - sperm. After pollination, a pollen tube is formed from the vegetative cell, through which sperm penetrate into the ovary of the pistil for fertilization.

The development of female germ cells in plants is called megagametogenesis(from Greek. megas- big). It occurs in the ovary of the pistil, which is preceded by megasporogenesis, as a result of which four megaspores are formed from the mother cell of the megaspore lying in the nucellus by meiotic division. One of the megaspores divides mitotically three times, giving rise to the female gametophyte, an embryo sac with eight nuclei. With the subsequent separation of the cytoplasms of the daughter cells, one of the resulting cells becomes an egg, on the sides of which lie the so-called synergids, three antipodes are formed at the opposite end of the embryo sac, and in the center, as a result of the fusion of two haploid nuclei, a diploid central cell is formed.

The development of germ cells in animals. In animals, two processes of the formation of germ cells are distinguished - spermatogenesis and oogenesis.

spermatogenesis(from Greek. sperm, spermatos- seed and genesis- origin, occurrence) is the process of formation of mature male germ cells - spermatozoa. In humans, it occurs in the testes, or testes, and is divided into four periods: reproduction, growth, maturation and formation.

IN breeding season primordial germ cells divide mitotically, resulting in the formation of diploid spermatogonia. IN growth period spermatogonia accumulate nutrients in the cytoplasm, increase in size and turn into primary spermatocytes, or spermatocytes of the 1st order. Only after that they enter meiosis ( ripening period), which first results in two secondary spermatocyte, or spermatocyte of the 2nd order, and then - four haploid cells with a fairly large amount of cytoplasm - spermatids. IN formation period they lose almost all of the cytoplasm and form a flagellum, turning into spermatozoa.

spermatozoa, or gummies, - very small mobile male sex cells with a head, neck and tail.

IN head, except for the core, is acrosome- a modified Golgi complex, which ensures the dissolution of the membranes of the egg during fertilization. IN neck there are centrioles of the cell center, and the basis ponytail form microtubules that directly support the movement of the spermatozoon. It also contains mitochondria, which provide the sperm with ATP energy for movement.

Ovogenesis(from Greek. UN- an egg and genesis- origin, occurrence) is the process of formation of mature female germ cells - eggs. In humans, it occurs in the ovaries and consists of three periods: reproduction, growth and maturation. Periods of reproduction and growth, similar to those in spermatogenesis, occur even during intrauterine development. At the same time, diploid cells are formed from the primary germ cells as a result of mitosis. oogonia, which then turn into diploid primary oocytes, or oocytes of the 1st order. Meiosis and subsequent cytokinesis occurring in ripening period, are characterized by uneven division of the cytoplasm of the mother cell, so that as a result, at first one is obtained secondary oocyte, or oocyte 2nd order, And first polar body, and then from the secondary oocyte - the egg, which retains the entire supply of nutrients, and the second polar body, while the first polar body is divided into two. Polar bodies take away excess genetic material.

In humans, eggs are produced with an interval of 28-29 days. The cycle associated with the maturation and release of eggs is called the menstrual cycle.

Egg- large female sex cell, which carries not only a haploid set of chromosomes, but also a significant supply of nutrients for the subsequent development of the embryo.

The egg in mammals is covered with four membranes, which reduce the likelihood of damage to it by various factors. The diameter of the egg in humans reaches 150-200 microns, while in an ostrich it can be several centimeters.

Cell division is the basis for the growth, development and reproduction of organisms. The role of mitosis and meiosis

If in unicellular organisms cell division leads to an increase in the number of individuals, i.e., reproduction, then in multicellular organisms this process may have different meaning. Thus, cell division of the embryo, starting from the zygote, is the biological basis for the interconnected processes of growth and development. Similar changes are seen in humans adolescence when the number of cells not only increases, but also a qualitative change occurs in the body. Reproduction of multicellular organisms is also based on cell division, for example, during asexual reproduction, due to this process, a whole body is restored from a part of the organism, and during sexual reproduction, germ cells are formed during gametogenesis, subsequently giving a new organism. It should be noted that the main methods of eukaryotic cell division - mitosis and meiosis - have different meanings in life cycles organisms.

As a result of mitosis, there is a uniform distribution of hereditary material between daughter cells - exact copies of the mother. Without mitosis, the existence and growth of multicellular organisms developing from a single cell, the zygote, would be impossible, since all cells of such organisms must contain the same genetic information.

In the process of division, daughter cells become more and more diverse in structure and functions, which is associated with the activation of new groups of genes in them due to intercellular interaction. Thus, mitosis is necessary for the development of an organism.

This method of cell division is necessary for the processes of asexual reproduction and regeneration (recovery) of damaged tissues, as well as organs.

Meiosis, in turn, ensures the constancy of the karyotype during sexual reproduction, as it reduces by half the set of chromosomes before sexual reproduction, which is then restored as a result of fertilization. In addition, meiosis leads to the appearance of new combinations of parental genes due to crossing over and random combination of chromosomes in daughter cells. Thanks to this, the offspring is genetically diverse, which provides material for natural selection and is the material basis of evolution. A change in the number, shape and size of chromosomes, on the one hand, can lead to the appearance of various deviations in the development of the organism and even its death, and on the other hand, it can lead to the appearance of individuals more adapted to the environment.

Thus, the cell is a unit of growth, development and reproduction of organisms.

Cell- the elementary unit of a living system. Various structures of a living cell, which are responsible for the performance of a particular function, are called organelles, like the organs of the whole organism. Specific functions in the cell are distributed among organelles, intracellular structures that have a certain shape, such as the cell nucleus, mitochondria, etc.

Cell structures:

Cytoplasm. Mandatory part of the cell, enclosed between the plasma membrane and the nucleus. Cytosol- This is a viscous aqueous solution of various salts and organic substances, permeated with a system of protein filaments - cytoskeletons. Most of the chemical and physiological processes of the cell take place in the cytoplasm. Structure: Cytosol, cytoskeleton. Functions: includes various organelles, the internal environment of the cell
plasma membrane. Each cell of animals, plants, is limited from the environment or other cells by the plasma membrane. The thickness of this membrane is so small (about 10 nm) that it can only be seen with an electron microscope.

Lipids they form a double layer in the membrane, and proteins penetrate its entire thickness, are immersed to different depths in the lipid layer, or are located on the outer and inner surfaces of the membrane. The structure of the membranes of all other organelles is similar to the plasma membrane. Structure: a double layer of lipids, proteins, carbohydrates. Functions: restriction, preservation of the shape of the cell, protection from damage, regulator of the intake and removal of substances.

Lysosomes. Lysosomes are membranous organelles. They have an oval shape and a diameter of 0.5 microns. They contain a set of enzymes that break down organic matter. The membrane of lysosomes is very strong and prevents the penetration of its own enzymes into the cytoplasm of the cell, but if the lysosome is damaged by any external influences, then the entire cell or part of it is destroyed.
Lysosomes are found in all cells of plants, animals and fungi.

Carrying out the digestion of various organic particles, lysosomes provide additional "raw materials" for chemical and energy processes in the cell. During starvation, lysosome cells digest some organelles without killing the cell. Such partial digestion provides the cell with the necessary minimum of nutrients for a while. Sometimes lysosomes digest whole cells and groups of cells, which plays an essential role in the developmental processes in animals. An example is the loss of the tail during the transformation of a tadpole into a frog. Structure: oval-shaped vesicles, membrane outside, enzymes inside. Functions: breakdown of organic substances, destruction of dead organelles, destruction of spent cells.

Golgi complex. The products of biosynthesis entering the lumens of the cavities and tubules of the endoplasmic reticulum are concentrated and transported in the Golgi apparatus. This organelle is 5–10 µm in size.

Structure: cavities surrounded by membranes (vesicles). Functions: accumulation, packaging, excretion of organic substances, formation of lysosomes

Endoplasmic reticulum. The endoplasmic reticulum is a system for the synthesis and transport of organic substances in the cytoplasm of a cell, which is an openwork structure of connected cavities.
A large number of ribosomes are attached to the membranes of the endoplasmic reticulum - the smallest organelles of the cell, having the form of a sphere with a diameter of 20 nm. and made up of RNA and protein. Ribosomes are where protein synthesis takes place. Then the newly synthesized proteins enter the system of cavities and tubules, through which they move inside the cell. Cavities, tubules, tubules from membranes, on the surface of ribosome membranes. Functions: synthesis of organic substances with the help of ribosomes, transport of substances.

Ribosomes. Ribosomes are attached to the membranes of the endoplasmic reticulum or are freely located in the cytoplasm, they are arranged in groups, and proteins are synthesized on them. Protein composition, ribosomal RNA Functions: provides protein biosynthesis (assembly of a protein molecule from).
Mitochondria. Mitochondria are energy organelles. The shape of mitochondria is different, they can be the rest, rod-shaped, filamentous with an average diameter of 1 micron. and 7 µm long. The number of mitochondria depends on the functional activity of the cell and can reach tens of thousands in the flying muscles of insects. Mitochondria are externally bounded by an outer membrane, under it is an inner membrane that forms numerous outgrowths - cristae.

Inside the mitochondria are RNA, DNA and ribosomes. Specific enzymes are built into its membranes, with the help of which the energy of food substances is converted into ATP energy in the mitochondria, which is necessary for the life of the cell and the organism as a whole.

Membrane, matrix, outgrowths - cristae. Functions: synthesis of an ATP molecule, synthesis of its own proteins, nucleic acids, carbohydrates, lipids, formation of its own ribosomes.

plastids. Only in the plant cell: leukoplasts, chloroplasts, chromoplasts. Functions: accumulation of reserve organic substances, attraction of pollinating insects, synthesis of ATP and carbohydrates. Chloroplasts are shaped like a disc or a ball with a diameter of 4-6 microns. With a double membrane - external and internal. Inside the chloroplast there are DNA ribosomes and special membrane structures - grana, connected to each other and to the inner membrane of the chloroplast. Each chloroplast has about 50 grains, staggered for better light capture. Chlorophyll is found in the gran membranes, thanks to which the energy of sunlight is converted into the chemical energy of ATP. The energy of ATP is used in chloroplasts for the synthesis of organic compounds, primarily carbohydrates.
Chromoplasts. Red and yellow pigments found in chromoplasts give various parts of the plant their red and yellow color. carrots, tomato fruits.

Leukoplasts are the place of accumulation of a reserve nutrient - starch. There are especially many leukoplasts in the cells of potato tubers. In the light, leukoplasts can turn into chloroplasts (as a result of which potato cells turn green). In autumn, chloroplasts turn into chromoplasts and green leaves and fruits turn yellow and red.

Cell Center. It consists of two cylinders, centrioles, located perpendicular to each other. Functions: support for spindle threads

Cellular inclusions either appear in the cytoplasm or disappear during the life of the cell.

Dense inclusions in the form of granules contain reserve nutrients (starch, proteins, sugars, fats) or cell waste products that cannot yet be removed. All plastids of plant cells have the ability to synthesize and accumulate reserve nutrients. In plant cells, the accumulation of reserve nutrients occurs in vacuoles.

Grains, granules, drops Functions: non-permanent formations that store organic matter and energy

Core. Nuclear envelope of two membranes, nuclear juice, nucleolus. Functions: storage of hereditary information in the cell and its reproduction, RNA synthesis - informational, transport, ribosomal. IN nuclear membrane there are spores, through which an active exchange of substances between the nucleus and the cytoplasm is carried out. The nucleus stores hereditary information not only about all the features and properties of a given cell, about the processes that should proceed to it (for example, protein synthesis), but also about the characteristics of the organism as a whole. Information is recorded in DNA molecules, which are the main part of chromosomes. The nucleus contains a nucleolus. The nucleus, due to the presence in it of chromosomes containing hereditary information, performs the functions of a center that controls all vital activity and development of the cell.

As you know, almost all organisms on our planet have a cellular structure. Basically, all cells have a similar structure. It is the smallest structural and functional unit of a living organism. Cells can have different functions and, consequently, variations in their structure. In many cases, they can act as independent organisms.

Plants, animals, fungi, bacteria have a cellular structure. However, there are some differences between their structural and functional units. And in this article we will consider the cellular structure. Grade 8 provides for the study of this topic. Therefore, the article will be of interest to schoolchildren, as well as to those who are simply interested in biology. This review will describe the various organisms, the similarities and differences between them.

History of the theory of cellular structure

People did not always know what organisms are made of. The fact that all tissues are formed from cells has become known relatively recently. The science that studies this is biology. The cellular structure of the body was first described by scientists Matthias Schleiden and Theodor Schwann. It happened in 1838. Then the structure consisted of the following provisions:

animals and plants of all kinds are formed from cells;

they grow by forming new cells;

the cell is the smallest unit of life;

An organism is a collection of cells.

Modern theory includes slightly different provisions, and there are a little more of them:

a cell can only come from a parent cell;

It does not consist of a simple collection of cells, but of those combined into tissues, organs and organ systems;

the cells of all organisms have a similar structure;

a cell is a complex system consisting of smaller functional units;

cell - the smallest structural unit capable of acting as an independent organism.

Cell structure

Since almost all living organisms have a cellular structure, it is worth considering the general characteristics of the structure of this element. First, all cells are divided into prokaryotic and eukaryotic. In the latter, there is a nucleus that protects the hereditary information recorded on DNA. In prokaryotic cells, it is absent, and DNA floats freely. All are built according to the following scheme. They have a shell - a plasma membrane, around which additional protective formations are usually located. Everything below it, except for the nucleus, is the cytoplasm. It consists of hyaloplasm, organelles and inclusions. Hyaloplasm is the main transparent substance that serves as the internal environment of the cell and fills all its space. Organelles are permanent structures that perform certain functions, that is, they ensure the vital activity of the cell. Inclusions are non-permanent formations that also play a particular role, but do so temporarily.

Cellular structure of living organisms

Now we will list the organelles that are the same for the cells of any living creature on the planet, except for bacteria. These are mitochondria, ribosomes, Golgi apparatus, endoplasmic reticulum, lysosomes, cytoskeleton. Bacteria are characterized by only one of these organelles - ribosomes. Now consider the structure and functions of each organelle separately.

Mitochondria

They provide intracellular respiration. Mitochondria play the role of a kind of "power plant", generating energy, which is necessary for the life of the cell, for the passage of certain chemical reactions in it.

They belong to two-membrane organelles, that is, they have two protective shells - external and internal. Under them is a matrix - an analogue of hyaloplasm in the cell. Cristae form between the outer and inner membranes. These are the folds that contain enzymes. These substances are needed in order to be able to carry out chemical reactions, due to which the energy necessary for the cell is released.

Ribosomes

They are responsible for protein metabolism, namely, for the synthesis of substances of this class. Ribosomes consist of two parts - subunits, large and small. This organelle has no membrane. Ribosome subunits unite only immediately before the process of protein synthesis, the rest of the time they are separated. Substances are produced here on the basis of information recorded on DNA. This information is supplied to the ribosomes with the help of tRNA, since it would be very impractical and dangerous to transport DNA here every time - the probability of its damage would be too high.

golgi apparatus

This organoid consists of stacks of flat cisterns. The functions of this organoid are that it accumulates and modifies various substances, and also participates in the formation of lysosomes.

Endoplasmic reticulum

It is divided into smooth and rough. The first is built from flat tubes. It is responsible for the production of steroids and lipids in the cell. Rough is so called because on the walls of the membranes of which it consists, there are numerous ribosomes. It performs a transport function. Namely, it transfers proteins synthesized there from ribosomes to the Golgi apparatus.

Lysosomes

They are which contain the enzymes necessary for the implementation of chemical reactions that occur in the process of intracellular metabolism. The largest number of lysosomes is observed in leukocytes - cells that perform an immune function. This is explained by the fact that they carry out phagocytosis and are forced to digest a foreign protein, which requires a large amount of enzymes.

cytoskeleton

It is the last organelle that is common to fungi, animals, and plants. One of its main functions is to maintain the shape of the cell. It is made up of microtubules and microfilaments. The former are hollow tubes made from the protein tubulin. Due to their presence in the cytoplasm, some organelles can move around the cell. In addition, cilia and flagella in unicellular organisms can also consist of microtubules. The second component of the cytoskeleton - microfilaments - consists of contractile proteins actin and myosin. In bacteria, this organelle is usually absent. But some of them are characterized by the presence of a cytoskeleton, however, a more primitive one, not as complex as that of fungi, plants and animals.

plant cell organelles

The cellular structure of plants has some features. In addition to the organelles listed above, vacuoles and plastids are also present. The former are designed to accumulate substances in it, including unnecessary ones, since it is often impossible to remove them from the cell due to the presence of a dense wall around the membrane. The fluid that is inside the vacuole is called cell sap. In the young, there are initially several small vacuoles, which, as it ages, merge into one large one. There are three types of plastids: chromoplasts, leucoplasts, and chromoplasts. The former are characterized by the presence of red, yellow or orange pigment in them. Chromoplasts in most cases are needed to attract pollinating insects or animals that are involved in the distribution of fruits along with seeds with a bright color. It is thanks to these organelles that flowers and fruits have a variety of colors. Chromoplasts can form from chloroplasts, which can be observed in autumn, when the leaves turn yellow-red, and also when the fruit ripens, when it gradually disappears completely. green color. The next type of plastids - leukoplasts - are designed to store substances such as starch, some fats and proteins. Chloroplasts carry out the process of photosynthesis, thanks to which plants obtain the necessary organic substances for themselves.

From six molecules of carbon dioxide and the same amount of water, a cell can receive one molecule of glucose and six oxygen, which is released into the atmosphere. Chloroplasts are two-membrane organelles. Their matrix contains thylakoids grouped into grana. These structures contain chlorophyll, and here the photosynthesis reaction takes place. In addition, the chloroplast matrix also contains its own ribosomes, RNA, DNA, special enzymes, starch grains and lipid drops. The matrix of these organelles is also called the stroma.

Features of mushrooms

These organisms also have a cellular structure. In ancient times, they were combined into one kingdom with plants purely according to outward sign However, with the advent of more advanced science, it became clear that this could not be done.

Firstly, fungi, unlike plants, are not autotrophs, they are not capable of producing organic substances themselves, but only feed on ready-made ones. Secondly, the cell of the fungus is more similar to the animal, although it has some features of the plant. A fungal cell, like a plant, is surrounded by a dense wall, but it does not consist of cellulose, but of chitin. This substance is difficult to digest by the body of animals, which is why mushrooms are considered heavy food. In addition to the organelles described above, which are characteristic of all eukaryotes, there is also a vacuole here - this is another similarity between fungi and plants. But plastids are not observed in the structure of the fungal cell. Between the wall and the cytoplasmic membrane there is a lomasome, the functions of which are still not fully understood. The rest of the structure of the fungal cell resembles an animal. In addition to organelles, inclusions such as fat drops and glycogen also float in the cytoplasm.

animal cells

They are characterized by all the organelles that were described at the beginning of the article. In addition, a glycocalyx is located on top of the plasma membrane - a membrane consisting of lipids, polysaccharides and glycoproteins. It is involved in the transport of substances between cells.

Core

Of course, in addition to common organelles, animal, plant, and fungal cells have a nucleus. It is protected by two shells in which there are pores. The matrix consists of karyoplasm (nuclear juice), in which chromosomes float with hereditary information recorded on them. There are also nucleoli, which are responsible for the formation of ribosomes and RNA synthesis.

prokaryotes

These include bacteria. The cellular structure of bacteria is more primitive. They don't have a nucleus. The cytoplasm contains organelles such as ribosomes. Surrounding the plasma membrane is a murein cell wall. Most prokaryotes are equipped with organelles of movement - mainly flagella. An additional protective shell, a mucous capsule, can also be located around the cell wall. In addition to the basic DNA molecules, the bacterial cytoplasm contains plasmids that contain information responsible for increasing the body's resistance to adverse conditions.

Are all organisms made up of cells?

Some believe that all living organisms have a cellular structure. But this is not true. There is such a kingdom of living organisms as viruses.

They are not made up of cells. This organism is represented by a capsid - a protein shell. Inside it is DNA or RNA, which contains a small amount of genetic information. A lipoprotein coat, which is called a supercapsid, can also be located around the protein shell. Viruses can only reproduce inside foreign cells. In addition, they are capable of crystallization. As you can see, the statement that all living organisms have a cellular structure is incorrect.

comparison table

After we have considered the structure of various organisms, let's summarize. So, the cellular structure, table:

	Animals	Plants	Mushrooms	bacteria
Core	Eat	Eat	Eat	No
cell wall	No	Yes, made of cellulose	Yes, from chitin	Yes, from murein
Ribosomes	Eat	Eat	Eat	Eat
Lysosomes	Eat	Eat	Eat	No
Mitochondria	Eat	Eat	Eat	No
golgi apparatus	Eat	Eat	Eat	No
cytoskeleton	Eat	Eat	Eat	Eat
Endoplasmic reticulum	Eat	Eat	Eat	No
cytoplasmic membrane	Eat	Eat	Eat	Eat
Additional shells	Glycocalyx	No	No	Mucous capsule

That, perhaps, is all. We examined the cellular structure of all organisms that exist on the planet.

Famous English naturalist and traveler Charles Robin Darwin in his book "The Origin of Species" convincingly proved that all life on Earth is changing, more simple shapes life give rise to more complex. The simplest living organisms that appeared 2-3 billion years ago are connected by a long chain of transformations with higher plants and animals that live on Earth at the present time. On the path of long historical development, there were numerous transformations and complications, the emergence of new, more and more perfect forms.

But all living organisms bear a trace of origin from the most distant ancestor. This trace is cellular structure.

Robert Hooke's first microscope

The study of the cellular structure became possible only after 17th century inventions of the microscope. One of the first inventors of the microscope was an English naturalist and inventor Robert Hooke. When the original model of the microscope was designed by him, a new, hitherto unseen world opened up before the astonished gaze of the scientist. With the help of his microscope, Hooke examined everything that came to hand.

Hooke's microscope was a very imperfect instrument. It gave a blurry, indistinct image. The magnifying instruments of the 18th century were also imperfect. That is why, until the middle of the 19th century, the structure of the smallest particles discovered by Hooke continued to remain unclear to scientists.

The structure and life of cells

If you look at the ripe juicy pulp of a watermelon, on a break in the pulp you can see tiny pink grains playing in the sun, like drops of dew. These are the cells of watermelon pulp. So much juice has accumulated in them that they have reached a size at which the cell becomes visible without a microscope. Closer to the crust, the cells become smaller. In a thin slice of the crust, under a microscope, rectangular boxes - cells are visible. Their walls - cell membranes - consist of a very strong substance - fiber. Under the protection of the shell are the main parts of the cell: a semi-liquid substance - protoplasm and a spherical body core. The watermelon pulp cell is one example of the structure of a plant cell. All organs of a plant - root, stem, leaves, flowers, fruits - consist of countless cells.

Structure animal cell differs from the plant only in the absence of a separate cell membrane and cell sap. The main parts - protoplasm and nucleus - are found in both plant and animal cells. This allows us to talk about the cellular structure of both plants and animals.

How cells reproduce

The ability of cells to reproduce is of great importance for the body. Millions of cells are constantly dying, having completed their vital task. Only about three weeks live red blood cells. The integumentary cells of our body exist for no more than a month, then turning into dead ones. horny scales. And if the supply of these cells was not replenished by constant reproduction, then the body would be threatened with a very quick death. But in the deep layers of the integumentary tissue of the skin, reproduction of young integumentary cells. Red blood cells are formed by the reproduction of young hematopoietic cells in bone marrow where the development of blood cells occurs.

Cell reproduction takes place by dividing in two. This reveals the remarkable phenomenon of exceptionally precise division of the cell nucleus into two equal parts. Daughter cells are similar to each other and indistinguishable from the parent cell. A cell of any type during reproduction forms only cells similar to itself.

All living beings and organisms do not consist of cells: plants, fungi, bacteria, animals, people. Despite the minimum size, all the functions of the whole organism are performed by the cell. Complex processes take place inside it, on which the viability of the body and the work of its organs depend.

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Structural Features

Scientists are studying structural features of the cell and principles of its work. It is possible to examine in detail the features of the cell structure only with the help of a powerful microscope.

All our tissues - skin, bones, internal organs are made up of cells that are construction material, there are different forms and size, each variety performs a specific function, but the main features of their structure are similar.

First, let's find out what underlies structural organization of cells. In the course of the research, scientists have found that the cellular foundation is membrane principle. It turns out that all cells are formed from membranes, which consist of a double layer of phospholipids, where from the outside and inside immersed protein molecules.

What property is characteristic for all types of cells: the same structure, as well as functionality - regulation of the metabolic process, the use of one's own genetic material (the presence and RNA), the production and consumption of energy.

At the basis of the structural organization of the cell, the following elements are distinguished that perform a specific function:

• membrane — cell wall is made up of fats and proteins. Its main task is to separate the substances inside from the external environment. The structure is semi-permeable: it is able to pass carbon monoxide;
• core- the central region and the main component, separated from other elements by a membrane. It is inside the nucleus that information about growth and development is located, the genetic material, presented in the form of DNA molecules that make up;
• cytoplasm is a liquid substance internal environment, where various vital processes take place, contains a lot of important components.

What does the cellular content consist of, what are the functions of the cytoplasm and its main components:

1. Ribosome- the most important organelle, which is necessary for the processes of protein biosynthesis from amino acids, proteins perform a huge number of vital tasks.
2. Mitochondria- another component located inside the cytoplasm. It can be described in one phrase - an energy source. Their function is to provide the components with power for further energy production.
3. golgi apparatus consists of 5 - 8 pouches, which are interconnected. The main task of this apparatus is the transfer of proteins to other parts of the cell to provide energy potential.
4. Cleaning of damaged elements is carried out lysosomes.
5. Is engaged in transportation endoplasmic reticulum, through which proteins move molecules of useful substances.
6. Centrioles responsible for reproduction.

Core

Since it is a cellular center, therefore, special attention should be paid to its structure and functions. This component is an essential element for all cells: it contains hereditary traits. Without the nucleus, the processes of reproduction and transmission of genetic information would become impossible. Look at the picture depicting the structure of the nucleus.

• The nuclear membrane, which is highlighted in lilac, lets in the necessary substances and releases them back through the pores - small holes.
• Plasma is a viscous substance, it contains all the other nuclear components.
• the core is located in the very center, has the shape of a sphere. His main function- the formation of new ribosomes.
• If you look at the central part of the cell in a section, you can see subtle blue weaves - chromatin, the main substance that consists of a complex of proteins and long strands of DNA that carry the necessary information.

cell membrane

Let's take a closer look at the work, structure and functions of this component. Below is a table that clearly shows the importance of the outer shell.

Chloroplasts

This is another very important component. But why was the chloroplast not mentioned earlier, you ask. Yes, because this component is found only in plant cells. The main difference between animals and plants lies in the mode of nutrition: in animals it is heterotrophic, while in plants it is autotrophic. This means that animals are not able to create, that is, synthesize organic substances from inorganic ones - they feed on ready-made organic substances. Plants, on the contrary, are capable of carrying out the process of photosynthesis and contain special components - chloroplasts. These are green plastids containing chlorophyll. With its participation, the energy of light is converted into the energy of chemical bonds of organic substances.

Interesting! Chloroplasts are concentrated in large volumes mainly in the aerial parts of plants - green fruits and leaves.

If you are asked a question: name an important structural feature of the organic compounds of a cell, then the answer can be given as follows.

• many of them contain carbon atoms, which have different chemical and physical properties, and are also able to connect with each other;
• are carriers, active participants in various processes occurring in organisms, or are their products. This refers to hormones, various enzymes, vitamins;
• can form chains and rings, which provides a variety of connections;
• are destroyed by heating and interaction with oxygen;
• atoms in the composition of molecules combine with each other using covalent bonds, do not decompose into ions and therefore interact slowly, reactions between substances take a very long time - for several hours and even days.

The structure of the chloroplast

fabrics

Cells can exist one at a time, as in unicellular organisms, but most often they are combined into groups of their own kind and form various tissue structures that make up the body. There are several types of tissues in the human body:

• epithelial- focused on the surface skin, organs, elements digestive tract and respiratory system;
• muscular- we move thanks to the contraction of the muscles of our body, we carry out a variety of movements: from the simplest movement of the little finger to high-speed running. By the way, the heartbeat also occurs due to the contraction of muscle tissue;
• connective tissue makes up to 80 percent of the mass of all organs and plays a protective and supporting role;
• nervous- forms nerve fibers. Thanks to it, various impulses pass through the body.

reproduction process

Throughout the life of an organism, mitosis occurs - this is the name for the process of division, consisting of four stages:

1. Prophase. The two centrioles of the cell divide and move in opposite directions. At the same time, the chromosomes form pairs, and the shell of the nucleus begins to break down.
2. The second stage is called metaphase. Chromosomes are located between the centrioles, gradually the outer shell of the nucleus completely disappears.
3. Anaphase is the third stage, during which the movement of centrioles continues in the opposite direction from each other, and individual chromosomes also follow the centrioles and move away from each other. The cytoplasm and the whole cell begin to shrink.
4. Telophase- the final stage. The cytoplasm shrinks until two identical new cells appear. A new membrane is formed around the chromosomes and one pair of centrioles appears in each new cell.

Interesting! Cells in the epithelium divide faster than in bone tissue. It all depends on the density of the fabrics and other characteristics. The average life expectancy of the main structural units is 10 days.

Cell structure. The structure and functions of the cell. Cell life.

Conclusion

You learned what the structure of the cell is the most important component of the body. Billions of cells make up an amazingly wisely organized system that ensures the efficiency and vitality of all representatives of the animal and plant world.