Similarities and differences in the structure of prokaryotic and eukaryotic cells - Knowledge Hypermarket. Structure of prokaryotic and eukaryotic cells Distinctive features of prokaryotes and eukaryotes

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 activities were continued by Koch.

Let's try to figure out which organisms belong to each of these two main classes of cells. What structure do cells have and what are their differences? 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 (superkingdom “Pre-nuclear”) and eukaryotes (superkingdom “Nuclear”).

Prokaryotes include:

To eukaryotes:

• mushrooms;
• plants;
• animals.

How are they different? Let's look at it below.

Signs of a eukaryotic cell

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

The signatures in each state one distinctive feature of 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 contains 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 - their structure resembles proteins, they also contain DNA;
• lysosomes - are vesicles that help the general metabolism of this cell;
• chloroplasts.

These connections are also separated by membranes, the main role of which is to connect the various elements of the organism unit with the external environment. In order for all the elements of the composition to function well, this cell has threads and microtubules for a complete “skeleton”.

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

Structure of prokaryotic cells

Unlike the previous superkingdom, protozoa do not have a nucleus in the cell.

Instead of a nucleus, there is one chromosome in the cytoplasm that transmits genetic material.

They reproduce simply by cell division. There is very little in the cellular fluid various types structures. They are also covered with a membrane. They contain ribosomes.

Let's look at the main representatives of this super-kingdom.

Bacteria and cyanobacteria

The former refers to unicellular 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 soil. They have autotrophic nutrition. Their buoyancy is determined by vacuoles. In addition, they, like representatives of the plant kingdom, are characterized by photosynthesis.

Examples include green algae. They also reproduce by simple division. At very unfavorable conditions can use spores for movement.

Similarities and differences between prokaryotes and eukaryotes

The comparative table “Characteristics of the Overkingdoms” shows signs by which it is easy to identify the main differences.

Conclusion

So, without representatives of these two super-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 and serve as a source of nutrition and respiration for plants.

Eukaryotes not only provide food for others, but are also the main regulating force of the population different types, that is, one of the mechanisms of natural selection.

This is the oldest group, appearing approximately 3.5 billion years ago; Moreover, these are the smallest organisms that have cellular structure. The properties of prokaryotes are summarized in table. 2.2. As a rule, prokaryotes are represented by single cells, although blue-green algae (cyanobacteria, Cyanobacteria) can form chains of cells called threads.

Some bacteria adhere to each other, forming characteristic clusters resembling bunches of grapes (Fig. 2.10), but the united cells remain completely independent of each other. An individual bacterial cell can only be seen with the help of, which is why they are called microorganisms. The science that studies bacteria bacteriology- forms an important branch.

Bacteria vary in size: their length ranges from 0.1 to 10 microns, and their average diameter is 1 micron. Thus, in bacterial cell there is enough space to fit 200 molecules of medium-sized globular proteins (5 nm in diameter) across it. Since such molecules are able to diffuse at a distance of approximately 60 microns per second, these organisms do not require any special transport mechanisms.

Bacteria can be found everywhere: in soil and dust, in water and air, inside and on surfaces, etc. Some bacteria thrive in hot springs with temperatures of 78°C or higher. Others are able to survive in very low temperatures and even survive certain periods of being frozen in ice. Bacteria are also found in deep crevices on the ocean floor at very high temperatures. high blood pressure and temperature 360°C. They begin the unique food chains in these areas of the ocean.

The number of bacteria is unimaginably large; it has been established that one gram of fertile soil contains 2.5 billion bacteria; in 1 cm 3 of fresh milk their content can exceed 3 billion. Together with fungi, bacteria are vitally important for all other organisms, since, by destroying organic substances as a result of their vital activity, they ensure the circulation of nutrients in nature. In addition, they are becoming increasingly important in human life, and not only because some of them are causative agents of various diseases, but also because, due to the variety of biochemical reactions occurring in them, they can be used in many biotechnological processes. This issue is discussed in more detail in Chap. 12.

Unity of cell structure.

The contents of any cell are separated from the external environment by a special structure - plasma membrane (plasmalemma). This isolation allows you to create a very special environment inside the cell, unlike what surrounds it. Therefore, processes that do not occur anywhere else can occur in the cell; they are called life processes.

The internal environment of a living cell, bounded by the plasma membrane, is called cytoplasm. It includes hyaloplasm(basic transparent substance) and cell organelles, as well as various non-permanent structures - inclusions. Organelles that are present in any cell also include ribosomes, where it happens protein synthesis.

The structure of eukaryotic cells.

Eukaryotes- These are organisms whose cells have a nucleus. Core- this is the very organelle of the eukaryotic cell in which the hereditary information recorded in the chromosomes is stored and from which the hereditary information is transcribed. Chromosome is a DNA molecule integrated with proteins. The core contains nucleolus- the place where other important organelles involved in protein synthesis are formed - ribosomes. But ribosomes are only formed in the nucleus, and they work (i.e. synthesize protein) in the cytoplasm. Some of them are free in the cytoplasm, and some are attached to membranes, forming a network, which is called endoplasmic.

Ribosomes- non-membrane organelles.

Endoplasmic reticulum is a network of membrane-bounded tubules. There are two types: smooth and granular. Ribosomes are located on the membranes of the granular endoplasmic reticulum, so proteins are synthesized and transported there. And the smooth endoplasmic reticulum is the site of synthesis and transport of carbohydrates and lipids. There are no ribosomes on it.

The synthesis of proteins, carbohydrates and fats requires energy, which is produced in the eukaryotic cell by the “energy stations” of the cell - mitochondria.

Mitochondria- double-membrane organelles in which the process of cellular respiration occurs. Organic compounds are oxidized on mitochondrial membranes and chemical energy is accumulated in the form of special energy molecules (ATP).

There is also a place in the cell where organic compounds can accumulate and from where they can be transported - this is Golgi apparatus, system of flat membrane bags. It is involved in the transport of proteins, lipids, and carbohydrates. Organelles of intracellular digestion are also formed in the Golgi apparatus - lysosomes.

Lysosomes- single-membrane organelles, characteristic of animal cells, contain enzymes that can break down proteins, carbohydrates, nucleic acids, lipids.

A cell may contain organelles that do not have a membrane structure, such as ribosomes and a cytoskeleton.

Cytoskeleton- This musculoskeletal system cells, includes microfilaments, cilia, flagella, a cell center that produces microtubules and centrioles.

There are organelles characteristic only of plant cells - plastids. There are: chloroplasts, chromoplasts and leucoplasts. The process of photosynthesis occurs in chloroplasts.

In plant cells also vacuoles- products cell activity, which are reservoirs of water and compounds dissolved in it. Eukaryotic organisms include plants, animals and fungi.

The structure of prokaryotic cells.

Prokaryotes- single-celled organisms whose cells do not have a nucleus.

Prokaryotic cells are small in size and store genetic material in the form of a circular DNA molecule (nucleoid). Prokaryotic organisms include bacteria and cyanobacteria, which were formerly called blue-green algae.

If a process occurs in prokaryotes aerobic respiration, then for this purpose special protrusions of the plasma membrane are used - mesosomes. If bacteria are photosynthetic, then the process of photosynthesis occurs on photosynthetic membranes - thylakoids.

Protein synthesis in prokaryotes occurs at ribosomes. IN prokaryotic cell few organelles.

Hypotheses of the origin of organelles of eukaryotic cells.

Prokaryotic cells appeared on Earth earlier than eukaryotic cells.

1) symbiotic hypothesis explains the mechanism of emergence of some organelles of the eukaryotic cell - mitochondria and photosynthetic plastids.

2) Intussusception hypothesis- states that the origin of the eukaryotic cell comes from the fact that the ancestral form was an aerobic prokaryote. The organelles in it arose as a result of invagination and detachment of parts of the shell, followed by functional specialization into the nucleus, mitochondria, chloroplasts of other organelles.

Prokaryotic cells are distinguished by their 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 a few small ribosomes and various inclusions in the form of granules of lipids and other substances. The genetic material (DNA) is not separated by membranes from the cytoplasm, there are no formed chromosomes, and a “chromosome” is conventionally called a single circular DNA molecule.

Eukaryotic cells are very complex units of living nature and are characterized by great structural and functional diversity (Fig. 37). Moreover, the shape of cells often depends on the functions they perform in a multicellular organism. However, the general structure of all eukaryotic cells is fundamentally similar. Eukaryotic cells have a well-formed nucleus, delimited from the cytoplasm by a shell of two membranes; chromosomes made of long twisted strands of DNA; a complete set of various organelles.

Difference between prokaryotic and eukaryotic cells It is especially clearly visible when comparing their main features (table).

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 cell nucleus and membrane organelles. Eukaryotes are living organisms that contain a nucleus and membrane organelles.

The cell is the fundamental component 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 look at one definition of life: "Living things are chemical organizations composed 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 of cells. The theory of biogenesis, proposed by Rudolf Virchow in 1858, states that all living cells arise from existing (living) cells and cannot arise spontaneously from nonliving matter.

The components of cells are enclosed in a membrane, which serves as a barrier between the outside world and the internal components of the cell. Cell membrane- a selective barrier, which means that it allows the passage of certain chemicals that maintain the balance necessary for the functioning of cells.

The cell membrane regulates movement chemicals 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 of ​​​​higher concentration towards an area of ​​​​lower until the concentration equalizes);
• 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 consisting of cells that do not have a cell nucleus or any membrane-bound organelles. This means that the genetic material 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-circuit. 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. In eukaryotes, the genetic material is located in the nucleus, and the DNA is organized into chromosomes. Eukaryotic organisms can be unicellular or multicellular. are eukaryotes. Eukaryotes also include plants, fungi and protozoa.

A typical eukaryotic cell includes:

• nucleolus;