Comparative characteristics of prokaryotes and eukaryotes. cell theory

All living organisms can be classified into one of two groups (prokaryotes or eukaryotes) depending on the basic structure of their cells. Prokaryotes are living organisms consisting of cells that do not have a cell nucleus and membrane organelles. Eukaryotes are living organisms that contain a nucleus and membrane organelles.

The cell is a fundamental part of our modern definition life and living beings. Cells are seen as the basic building blocks of life and are used in defining what it means to be "alive".

Let's take a look at one definition of life: "Living beings are chemical organizations made up of cells and capable of reproducing" (Keaton, 1986). This definition is based on two theories - cell theory and theories of biogenesis. was first proposed in the late 1830s by German scientists Matthias Jakob Schleiden and Theodor Schwann. They argued that all living things are made up of cells. The theory of biogenesis, proposed by Rudolf Virchow in 1858, states that all living cells arise from existing (living) cells and cannot spontaneously arise from non-living matter.

The components of cells are enclosed in a membrane that acts as a barrier between the outside world and the internal components of the cell. cell membrane- a selective barrier, which means that it passes some chemicals that maintain the balance necessary for the vital activity of cells.

The cell membrane regulates movement chemical substances from cell to cell in the following ways:

• diffusion (the tendency of molecules of a substance to minimize concentration, that is, the movement of molecules from an area with a higher concentration towards an area with a lower one until the concentration is equalized);
• osmosis (the movement of solvent molecules through a partially permeable membrane in order to equalize the concentration of a solute that is unable to move through the membrane);
• selective transport (using membrane channels and pumps).

Prokaryotes are organisms composed of cells that do not have a cell nucleus or any membrane organelles. This means that the genetic material of DNA in prokaryotes is not bound in the nucleus. In addition, the DNA of prokaryotes is less structured than that of eukaryotes. In prokaryotes, DNA is single-loop. Eukaryotic DNA is organized into chromosomes. Most prokaryotes consist of only one cell (unicellular), but there are a few that are multicellular. Scientists divide prokaryotes into two groups: and.

A typical prokaryotic cell includes:

• plasma (cell) membrane;
• cytoplasm;
• ribosomes;
• flagella and pili;
• nucleoid;
• plasmids;

eukaryotes

Eukaryotes are living organisms whose cells contain a nucleus and membrane organelles. The genetic material in eukaryotes is located in the nucleus, and DNA is organized into chromosomes. eukaryotic organisms may be unicellular or multicellular. are eukaryotes. Also eukaryotes include plants, fungi and protozoa.

A typical eukaryotic cell includes:

• nucleolus;

There are only two types of organisms on Earth: eukaryotes and prokaryotes. They differ greatly in their structure, origin and evolutionary development, which will be discussed in detail below.

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Signs of a prokaryotic cell

Prokaryotes are otherwise called pre-nuclear. A prokaryotic cell does not have other organelles that have a membrane sheath (, endoplasmic reticulum, Golgi complex).

Also characteristic features for them are the following:

1. without a shell and does not form bonds with proteins. Information is transmitted and read continuously.
2. All prokaryotes are haploid organisms.
3. Enzymes are located in a free state (diffusely).
4. They have the ability to sporulate adverse conditions.
5. The presence of plasmids - small extrachromosomal DNA molecules. Their function is to convey genetic information, increasing resistance to many aggressive factors.
6. The presence of flagella and pili - external protein formations necessary for movement.
7. Gas vacuoles are cavities. Due to them, the body is able to move in the water column.
8. The cell wall in prokaryotes (specifically bacteria) consists of murein.
9. The main methods of obtaining energy in prokaryotes are chemo- and photosynthesis.

These include bacteria and archaea. Examples of prokaryotes: spirochetes, proteobacteria, cyanobacteria, krenarcheotes.

Attention! Despite the fact that prokaryotes lack a nucleus, they have its equivalent - a nucleoid (a circular DNA molecule devoid of shells), and free DNA in the form of plasmids.

The structure of a prokaryotic cell

bacteria

Representatives of this kingdom are among the most ancient inhabitants of the Earth and have a high survival rate in extreme conditions.

There are gram-positive and gram-negative bacteria. Their main difference lies in the structure of the cell membrane. Gram-positive have a thicker shell, up to 80% consists of a murein base, as well as polysaccharides and polypeptides. When stained by Gram they give a purple color. Most of these bacteria are pathogens. Gram-negative ones have a thinner wall, which is separated from the membrane by the periplasmic space. However, such a shell has increased strength and is much more resistant to the effects of antibodies.

Bacteria play a very important role in nature:

1. Cyanobacteria (blue-green algae) help maintain the right level of oxygen in the atmosphere. They form more than half of all O2 on Earth.
2. They contribute to the decomposition of organic remains, thereby taking part in the cycle of all substances, participate in the formation of soil.
3. Nitrogen fixers on the roots of legumes.
4. They purify water from waste, for example, the metallurgical industry.
5. They are part of the microflora of living organisms, helping to absorb nutrients as much as possible.
6. They are used in the food industry for fermentation. This is how cheeses, cottage cheese, alcohol, and dough are obtained.

Attention! Apart from positive value bacteria also play a role. Many of them cause deadly dangerous diseases such as cholera, typhoid fever, syphilis, tuberculosis.

bacteria

Archaea

Previously, they were combined with bacteria into a single kingdom of Drobyanok. However, over time, it became clear that archaea have their own individual evolutionary path and are very different from other microorganisms in their biochemical composition and metabolism. Up to 5 types are distinguished, the most studied are Euryarchaeots and Crenarchaeotes. Archaeal features are:

• most of them are chemoautotrophs - they synthesize organic substances from carbon dioxide, sugar, ammonia, metal ions and hydrogen;
• play a key role in the nitrogen and carbon cycle;
• participate in digestion in humans and many ruminants;
• have a more stable and durable membrane shell due to the presence of ether bonds in glycerol-ether lipids. This allows archaea to live in highly alkaline or acidic environments, as well as under conditions of high temperatures;
• the cell wall, unlike bacteria, does not contain peptidoglycan and consists of pseudomurein.

The structure of eukaryotes

Eukaryotes are a kingdom of organisms whose cells contain a nucleus. In addition to archaea and bacteria, all living things on Earth are eukaryotes (for example, plants, protozoa, animals). Cells can vary greatly in their shape, structure, size, and function. Despite this, they are similar in the basics of life, metabolism, growth, development, ability to irritate and variability.

Eukaryotic cells can be hundreds or thousands of times larger than prokaryotic cells. They include the nucleus and cytoplasm with numerous membranous and non-membrane organelles. Membrane include: endoplasmic reticulum, lysosomes, Golgi complex, mitochondria,. Non-membrane: ribosomes, cell center, microtubules, microfilaments.

The structure of eukaryotes

Let us compare eukaryotic cells from different kingdoms.

The kingdoms of eukaryotes include:

• protozoa. Heterotrophs, some capable of photosynthesis (algae). They reproduce asexually, sexually and in a simple way into two parts. Most do not have a cell wall;
• plants. They are producers, the main way to obtain energy is photosynthesis. Most plants are immobile and reproduce asexually, sexually and vegetatively. The cell wall is made up of cellulose;
• mushrooms. Multicellular. Distinguish between lower and higher. They are heterotrophic organisms and cannot move independently. They reproduce asexually, sexually and vegetatively. Store glycogen and have a strong cell wall from chitin;
• animals. There are 10 types: sponges, worms, arthropods, echinoderms, chordates and others. They are heterotrophic organisms. capable of independent movement. The main storage substance is glycogen. The cell wall is made up of chitin, just like in fungi. The main mode of reproduction is sexual.

Table: Comparative characteristics vegetable and animal cell

Comparison of prokaryotes and eukaryotes

The structural features of prokaryotic and eukaryotic cells are significant, but one of the main differences concerns the storage of genetic material and the way energy is obtained.

Prokaryotes and eukaryotes photosynthesize differently. In prokaryotes, this process takes place on membrane outgrowths (chromatophores) stacked in separate piles. Bacteria do not have a fluorine photosystem, therefore they do not release oxygen, unlike blue-green algae, which form it during photolysis. The sources of hydrogen in prokaryotes are hydrogen sulfide, H2, various organic substances and water. The main pigments are bacteriochlorophyll (in bacteria), chlorophyll and phycobilins (in cyanobacteria).

Of all the eukaryotes, only plants are capable of photosynthesis. They have special formations - chloroplasts containing membranes laid in grana or lamellae. The presence of photosystem II allows oxygen to be released into the atmosphere during the process of water photolysis. The only source of hydrogen molecules is water. The main pigment is chlorophyll, and phycobilins are present only in red algae.

Main differences and characteristics prokaryotes and eukaryotes are presented in the table below.

Table: Similarities and differences between prokaryotes and eukaryotes

Differences between prokaryotes and eukaryotes

Similarities and differences between prokaryotic and eukaryotic cells

Conclusion

Comparison of a prokaryotic and eukaryotic organism is a rather laborious process that requires consideration of many nuances. They have much in common with each other in terms of structure, ongoing processes and properties of all living things. The differences lie in the functions performed, the methods of nutrition and internal organization. Those who are interested in this topic can use this information.

Prokaryotic cells differ in very small sizes (from 0.5 to 5 microns) and the simplest structure (Fig. 36). They have immobile cytoplasm plasma membrane and cell wall. The cytoplasm contains few small ribosomes and various inclusions in the form of lipid granules and other substances. The genetic material (DNA) is not separated by membranes from the cytoplasm, there are no well-formed chromosomes, and a single circular DNA molecule is conventionally called a “chromosome”.

eukaryotic cells are very complex units of wildlife and are characterized by a large structural and functional diversity (Fig. 37). In this case, the shape of cells often depends on the functions they perform in a multicellular organism. However, the general plan of the structure of all eukaryotic cells has a fundamental similarity. In eukaryotic cells, there is a well-formed nucleus, delimited from the cytoplasm by a sheath of two membranes; chromosomes of long twisted strands of DNA; a complete set of various organelles.

The difference between prokaryotes and eukaryotes especially well seen when comparing their main features (table).

A cell is an elementary structural and functional unit of the structure and life of all organisms, which has its own metabolism and is capable of independent existence, self-reproduction. Organisms consisting of one cell are called unicellular. Many protozoa (sarcodes, flagellates, sporozoans, ciliates) and bacteria can be attributed to unicellular organisms. Each cell in its composition has up to 80% water, and only the rest falls on the mass of dry matter.

Features of the structure of cells

All cell forms life, based on the structural features of their constituent cells, can be divided into two types (superkingdoms):
1. Prokaryotes (pre-nuclear) - those that arose earlier in the process of evolution and are simpler in structure. These are unicellular living organisms that do not have a formalized cell nucleus and other internal membrane organelles. The average cell diameter is 0.5-10 microns. It has one circular DNA molecule located in the cytoplasm. Has simple binary fission. In this case, the fission spindle is not formed;
2. Eukaryotes (nuclear) - which arose later more complex cells. All organisms except bacteria and archaea are nuclear. Each nuclear cell contains a kernel. The average cell diameter is 10-100 microns. Usually has several linear DNA molecules (chromosomes) located in the nucleus. It has the division of meiosis or mitosis. Forms a spindle of division.

In turn, eukaryotes can also be divided into two types (kingdoms):
1. Plant cells;
2. Animal cells.

The structural features of an animal cell can be seen in the picture above. The cell can be divided into the following parts:
1. Cell membrane;
2. Cytoplasm or cytazol;
3. Cytoskeleton;
4. Centrioles;
5. Golgi apparatus;
6. Lysosome;
7. Ribosome;
8. Mitochondria;


11. Core;
12. Nucleolus;
13. Peroxisome.

The structural features of a plant cell can also be seen in the picture above. The cell can be divided into the following parts:
1. Cell membrane;
2. Cytoplasm or cytazol;
3. Cytoskeleton;
4. Pores;
5. Golgi apparatus;
6. Central vacuole;
7. Ribosome;
8. Mitochondria;
9. Rough endoplasmic reticulum;
10. Smooth endoplasmic reticulum;
11. Core;
12. Nucleolus.

Structural features of eukaryotic and prokaryotic cells

One can write a whole article about the structural features of eukaryotic and prokaryotic cells, but still we will try to highlight only the important parts and analyze the difference between one superkingdom over another. We begin to describe the difference by moving to the core.

One of the important classifications in cell biology is their division into prokaryotes and eukaryotes.

Speaking about the evolution of microbiology, it is worth noting the significant contribution of the scientist Pasteur, who was its founder. It was thanks to this man that the fields of immunology and biotechnology began to develop.

He gave a basic definition of the main concepts related to the cell, substantiated the principles and operation of the mechanism on the relevance of the role of microorganisms in all spheres of life of organisms. His work was continued by Koch.

Let's try to figure out which organisms belong to each of these two main classes of cells. What is the structure of cells and how do they differ? What is the classification of each of these types.

How are they useful for humans and the biosphere, and what is their significance in general? The reader will find answers to all these questions below.

What are prokaryotes and eukaryotes

It is known that all living organisms by their nature are divided into cellular and non-cellular (viruses). Moreover, the former are also divided into 2 categories: prokaryotes (the pre-nuclear kingdom) and eukaryotes (the nuclear kingdom).

Prokaryotes include:

For eukaryotes:

• mushrooms;
• plants;
• animals.

How are they different? Consider below.

Signs of a eukaryotic cell

It is believed that nuclear cellular organisms appeared about 1.5 billion years ago. Although in the past, scientists poorly understood the essence of phenomena at the cellular level, but in their writings they often began to appear approximate drawings of this unit of the organism.

Signatures in each state one distinguishing feature cells of this type - the presence of a nucleus covered with a double layer of membrane.

It is in the nucleus that the main genetic material of these organisms is stored. In addition, it has several nucleoli with most of the volume of all types of RNA.

Also in such a cell there are other formations - organelles that are located in its cytoplasm. These include:

• mitochondria - resemble proteins in their structure, also contain DNA;
• lysosomes - are vesicles that help the overall metabolism of this cell;
• chloroplasts.

These compounds are also separated by membranes, the main role of which is the connection of the various elements of the organism unit with the external environment. In order for all the elements of the composition to function well, for a complete "skeleton" in this cell there are filaments and microtubules.

The process of respiration is more common among living organisms formed by these cells.

The structure of prokaryotic cells

Unlike the previous superkingdom, protozoa lack a nucleus in the cell.

In it, instead of the nucleus, there is one chromosome in the cytoplasm, which transmits the genetic material.

They reproduce simply by cell division. Very little in cell fluid various kinds structures. They are also covered with a membrane. They contain ribosomes.

Consider the main representatives of this super-kingdom.

Bacteria and cyanobacteria

The former are single-celled microorganisms. With the help of flagella, they are very mobile.

They live in all areas of life. From external environment they are protected by murein and a special shell.

The second type is represented by the simplest cells with small ribosomes and one hereditary chromosome.

Seaweed

They live mainly in aquatic environment and on the ground. They have autotrophic nutrition. Their buoyancy is determined by vacuoles. In addition, for them, as for representatives of the plant kingdom, photosynthesis is characteristic.

Examples are represented by green algae. They also reproduce by simple division. Under very unfavorable conditions, spores can be used for movement.

Similarities and differences between prokaryotes and eukaryotes

The comparative table "Characteristics of the super-kingdoms" shows signs by which it is easy to identify the main differences.

Conclusion

So, without representatives of these two kingdoms it is impossible to imagine life on earth. What is their role in nature? It's simple: protozoa are organisms without which almost all biochemical processes in a biosystem are impossible. In addition, many are involved in the process of photosynthesis, serve as a source of nutrition and respiration for plants.

Eukaryotes are not only food for others, but also the main regulatory force of the population. different types, i.e., one of the mechanisms of natural selection.