Prokaryotes and eukaryotes briefly. What are eukaryotes? Are they bacteria? Additional eukaryotic differences

All are eukaryotic organisms. They can be unicellular or multicellular, but all have a common cell structure. All these very dissimilar organisms are believed to have a common origin, so the nuclear group is considered the highest-ranking monophyletic taxon. According to the most common hypotheses, eukaryotes appeared 1.5–2 billion years ago. An important role in the evolution of eukaryotes was played by symbiogenesis - a symbiosis between a eukaryotic cell, apparently already having a nucleus and capable of phagocytosis, and bacteria absorbed by this cell - the precursors of mitochondria and plastids.

Structure of a eukaryotic cell

Eukaryotic cells are on average much larger than prokaryotic cells, the difference in volume reaches thousands of times. Eukaryotic cells include about a dozen types of different structures known as organelles (or organelles, which, however, somewhat distorts the original meaning of this term), of which many are separated from the cytoplasm by one or more membranes (in prokaryotic cells, internal organelles surrounded by a membrane are rare ). The nucleus is a part of the cell, surrounded in eukaryotes by a double membrane (two elementary membranes) and containing genetic material: DNA molecules, “packed” into chromosomes. There is usually one nucleus, but there are also multinucleated cells.

Division into kingdoms

There are several options for dividing the eukaryotic superkingdom into kingdoms. The plant and animal kingdoms were the first to be distinguished. Then the kingdom of fungi was identified, which, due to their biochemical characteristics, according to most biologists, cannot be classified as one of these kingdoms. Also, some authors distinguish the kingdoms of protozoa, myxomycetes, and chromists. Some systems have up to 20 kingdoms. According to the Thomas Cavalier-Smith system, all eukaryotes are divided into two monophyletic taxa - Unikonta And Bikonta. The position of eukaryotes such as Collodictyon ( Collodictyon) And Diphylleia, currently undefined.

Differences between eukaryotes and prokaryotes

The most important, fundamental feature of eukaryotic cells is associated with the location of the genetic apparatus in the cell. The genetic apparatus of all eukaryotes is located in the nucleus and is protected by the nuclear envelope (in Greek, “eukaryote” means having a nucleus). The DNA of eukaryotes is linear (in prokaryotes, the DNA is circular and is located in a special region of the cell - the nucleoid, which is not separated by a membrane from the rest of the cytoplasm). It is associated with histone proteins and other chromosomal proteins that bacteria do not have.

In the life cycle of eukaryotes, there are usually two nuclear phases (haplophase and diplophase). The first phase is characterized by a haploid (single) set of chromosomes, then, merging, two haploid cells (or two nuclei) form a diploid cell (nucleus) containing a double (diploid) set of chromosomes. Sometimes during the next division, and more often after several divisions, the cell again becomes haploid. Such a life cycle and, in general, diploidity are not typical for prokaryotes.

The third, perhaps the most interesting difference, is the presence in eukaryotic cells of special organelles that have their own genetic apparatus, reproduce by division and are surrounded by a membrane. These organelles are mitochondria and plastids. In their structure and life activity they are strikingly similar to bacteria. This circumstance has prompted modern scientists to believe that such organisms are descendants of bacteria that entered into a symbiotic relationship with eukaryotes. Prokaryotes are characterized by a small number of organelles, and none of them are surrounded by a double membrane. Prokaryotic cells do not have an endoplasmic reticulum, Golgi apparatus, or lysosomes.

Another important difference between prokaryotes and eukaryotes is the presence of endocytosis in eukaryotes, including phagocytosis in many groups. Phagocytosis (literally “eating by a cell”) is the ability of eukaryotic cells to capture, enclose in a membrane vesicle, and digest a wide variety of solid particles. This process provides an important protective function in the body. It was first discovered by I.I. Mechnikov in starfish. The appearance of phagocytosis in eukaryotes is most likely associated with average size (more about size differences is written below). The sizes of prokaryotic cells are disproportionately smaller, and therefore, in the process of evolutionary development of eukaryotes, they had the problem of supplying the body with a large amount of food. As a result, the first real, mobile predators appear among eukaryotes.

Most bacteria have a cell wall that is different from the eukaryotic one (not all eukaryotes have it). In prokaryotes, it is a durable structure consisting mainly of murein (in archaea, pseudomurein). The structure of murein is such that each cell is surrounded by a special mesh sac, which is one huge molecule. Among eukaryotes, many protists, fungi and plants have a cell wall. In fungi it consists of chitin and glucans, in lower plants it consists of cellulose and glycoproteins, diatoms synthesize a cell wall from silicic acids, in higher plants it consists of cellulose, hemicellulose and pectin. Apparently, for larger eukaryotic cells it has become impossible to create a cell wall of high strength from a single molecule. This circumstance could force eukaryotes to use different material for the cell wall. Another explanation is that the common ancestor of eukaryotes lost its cell wall due to the transition to predation, and then the genes responsible for the synthesis of murein were also lost. When some eukaryotes returned to osmotrophic nutrition, the cell wall appeared again, but on a different biochemical basis.

The metabolism of bacteria is also diverse. In general, there are four types of nutrition, and all are found among bacteria. These are photoautotrophic, photoheterotrophic, chemoautotrophic, chemoheterotrophic (phototrophic use the energy of sunlight, chemotrophic use chemical energy). Eukaryotes either synthesize energy from sunlight themselves or use ready-made energy of this origin. This may be due to the emergence of predators among eukaryotes, for which the need to synthesize energy has disappeared.

Another difference is the structure of the flagella. In bacteria they are thin - only 15–20 nm in diameter. These are hollow filaments made from the protein flagellin. The structure of eukaryotic flagella is much more complex. They are a cell outgrowth surrounded by a membrane and contain a cytoskeleton (axoneme) of nine pairs of peripheral microtubules and two microtubules in the center. Unlike rotating prokaryotic flagella, eukaryotic flagella bend or wriggle.

The two groups of organisms we are considering, as already mentioned, are very different in their average sizes. The diameter of a prokaryotic cell is usually 0.5–10 μm, while the same figure for eukaryotes is 10–100 μm. The volume of such a cell is 1000–10000 times greater than that of a prokaryotic cell.

Prokaryotic ribosomes are small (70S type). Eukaryotic cells contain both larger 80S-type ribosomes located in the cytoplasm and prokaryotic-type 70s ribosomes located in mitochondria and plastids.

Apparently, the time of emergence of these groups also differs. The first prokaryotes arose in the process of evolution about 3.5 billion years ago, from them about 1.2 billion years ago eukaryotic organisms evolved.

see also

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Which have a core. Almost all organisms are eukaryotes, except bacteria (viruses belong to a separate category, which not all biologists distinguish as a category of living beings). Eukaryotes include plants, animals, mushrooms and such living organisms as slime mold. Eukaryotes are divided into single-celled organisms And multicellular, but the principle of cell structure is the same for all of them.

It is believed that the first eukaryotes appeared about 2 billion years ago and evolved largely due to symbiogenesis- the interaction of eukaryotic cells and bacteria, which these cells absorbed, being capable of phagocytosis.

Eukaryotic cells They are very large in size, especially compared to prokaryotic ones. A eukaryotic cell has about ten organelles, most of which are separated by membranes from the cytoplasm, which is not the case in prokaryotes. Eukaryotes also have a nucleus, which we have already discussed. This is the part of the cell that is fenced off from the cytoplasm by a double membrane. It is in this part of the cell that the DNA contained in the chromosomes is located. The cells are usually mononucleated, but multinucleated cells are sometimes found.

Kingdoms of eukaryotes.

There are several options for dividing eukaryotes. Initially, all living organisms were divided only into plants and animals. Subsequently, the kingdom of mushrooms was identified, which differ significantly from both the first and the second. Even later, slime molds began to be isolated.

Slime mold is a polyphyletic group of organisms that some classify as the simplest, but the final classification of these organisms has not been fully classified. At one stage of development, these organisms have a plasmodic form - this is a slimy substance that does not have clear hard covers. In general, slime molds look like one multinucleate cell, which is visible to the naked eye.

Slime molds are related to fungi by sporulation, which germinate as zoospores, from which plasmodium subsequently develops.

Slime molds are heterotrophs capable of feeding inspectively, that is, absorb nutrients directly through the membrane, or endocytosis - take vesicles with nutrients inside. Slime molds include Acrasiaceae, Myxomycetes, Labyrinthulae and Plasmodiophorae.

Differences between prokaryotes and eukaryotes.

The main difference prokaryote and eukaryotes is that prokaryotes do not have a formed nucleus, separated by a membrane from the cytoplasm. In prokaryotes, circular DNA is found in the cytoplasm, and the place where the DNA is located is called the nucleoid.

Additional differences between eukaryotes.

1. Of the organelles, prokaryotes have only ribosomes 70S (small), and eukaryotes have not only large 80S ribosomes, but also many other organelles.
2. Since prokaryotes do not have a nucleus, they divide by fission in two - not with the help meiosis/mitosis.
3. Eukaryotes have histones that bacteria do not. Chromantin in eukaryotes contains 1/3 DNA and 2/3 protein; in prokaryotes the opposite is true.
4. A eukaryotic cell is 1000 times larger in volume and 10 times larger in diameter than a prokaryotic cell.

The most obvious The difference between prokaryotes and eukaryotes is that the latter have a nucleus, which is reflected in the names of these groups: “karyo” is translated from ancient Greek as core, “pro” - before, “eu” - good. Hence, prokaryotes are prenuclear organisms, eukaryotes are nuclear.

However, this is far from the only and perhaps not the main difference between prokaryotic organisms and eukaryotes. Prokaryotic cells do not have membrane organelles at all.(with rare exceptions) - mitochondria, chloroplasts, Golgi complex, endoplasmic reticulum, lysosomes. Their functions are performed by outgrowths (invaginations) of the cell membrane, on which various pigments and enzymes are located that ensure vital processes.

Prokaryotes do not have the chromosomes characteristic of eukaryotes. Their main genetic material is nucleoid, usually shaped like a ring. In eukaryotic cells, chromosomes are complexes of DNA and histone proteins (play an important role in DNA packaging). These chemical complexes are called chromatin. The nucleoid of prokaryotes does not contain histones, and the RNA molecules associated with it give it its shape.

Eukaryotic chromosomes are found in the nucleus. In prokaryotes, the nucleoid is located in the cytoplasm and is usually attached in one place to the cell membrane.

In addition to the nucleoid, prokaryotic cells have different amounts plasmids- nucleoids significantly smaller in size than the main one.

The number of genes in the nucleoid of prokaryotes is an order of magnitude less than in chromosomes. Eukaryotes have many genes that perform a regulatory function in relation to other genes. This allows eukaryotic cells of a multicellular organism that contain the same genetic information to specialize; by changing your metabolism, respond more flexibly to changes in the external and internal environment. The structure of the genes is also different. In prokaryotes, genes in DNA are arranged in groups called operons. Each operon is transcribed as a single unit.

There are also differences between prokaryotes and eukaryotes in the processes of transcription and translation. The most important thing is that in prokaryotic cells these processes can occur simultaneously on one molecule of messenger (messenger) RNA: while it is still being synthesized on DNA, ribosomes are already “sitting” at its finished end and synthesizing protein. In eukaryotic cells, mRNA undergoes so-called maturation after transcription. And only after that can protein be synthesized on it.

The ribosomes of prokaryotes are smaller (sedimentation coefficient 70S) than those of eukaryotes (80S). The number of proteins and RNA molecules in the ribosomal subunits differs. It should be noted that the ribosomes (as well as the genetic material) of mitochondria and chloroplasts are similar to prokaryotes, which may indicate their origin from ancient prokaryotic organisms that ended up inside the host cell.

Prokaryotes are usually distinguished by a more complex structure of their shells. In addition to the cytoplasmic membrane and cell wall, they also have a capsule and other structures, depending on the type of prokaryotic organism. The cell wall performs a supporting function and prevents the penetration of harmful substances. The bacterial cell wall contains murein (a glycopeptide). Among eukaryotes, plants have a cell wall (its main component is cellulose), and fungi have chitin.

Prokaryotic cells divide by binary fission. They have there are no complex processes of cell division (mitosis and meiosis), characteristic of eukaryotes. Although before division the nucleoid doubles, just like chromatin in chromosomes. In the life cycle of eukaryotes, there is an alternation of diploid and haploid phases. In this case, the diploid phase usually predominates. Unlike them, prokaryotes do not have this.

Eukaryotic cells vary in size, but in any case they are significantly larger than prokaryotic cells (tens of times).

Nutrients enter prokaryotic cells only through osmosis. In eukaryotic cells, in addition, phago- and pinocytosis (the “capture” of food and liquid using the cytoplasmic membrane) can also be observed.

In general, the difference between prokaryotes and eukaryotes lies in the clearly more complex structure of the latter. It is believed that prokaryotic cells arose through abiogenesis (long-term chemical evolution under the conditions of the early Earth). Eukaryotes appeared later from prokaryotes, through their unification (symbiotic and also chimeric hypotheses) or the evolution of individual representatives (invagination hypothesis). The complexity of eukaryotic cells allowed them to organize a multicellular organism and, in the process of evolution, provide all the basic diversity of life on Earth.

Table of differences between prokaryotes and eukaryotes

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 component of our modern definition of life and living things. 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 - the cell theory and the theory 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. The cell membrane is a selective barrier, meaning that it allows certain chemicals to pass through to maintain the balance necessary for cell function.

The cell membrane regulates the movement of 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;

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Eukaryotes

Material from Wikipedia - the free encyclopedia

Diagram of a typical animal cell. Noted organelles (organelles) 1. Nucleolus 2. Nucleus 3. Ribosome 4. Vesicle 5. Rough (granular) endoplasmic reticulum 6. Golgi apparatus 7. Cell wall 8. Smooth (agranular) endoplasmic reticulum 9. Mitochondrion 10. Vacuole 11. Hyalope lasma 12. Lysosome 13. Centrosome (Centriole)

Eukaryotes, or Nuclear(lat. Eucaryota from Greek εύ- - good and κάρυον - nucleus) - a superkingdom of living organisms whose cells contain nuclei. All organisms except bacteria and archaea are nuclear.

Structure of a eukaryotic cell

Eukaryotic cells are on average much larger than prokaryotic cells, the difference in volume reaches thousands of times. Eukaryotic cells include about a dozen types of different structures known as organelles (or organelles, which, however, somewhat distorts the original meaning of this term), many of which are separated from the cytoplasm by one or more membranes. Prokaryotic cells always contain a cell membrane, ribosomes (substantially different from eukaryotic ribosomes) and genetic material - a bacterial chromosome, or genophore, but internal organelles surrounded by a membrane are rare. The nucleus is a part of the cell, surrounded in eukaryotes by a double membrane (two elementary membranes) and containing genetic material: DNA molecules, “packed” into chromosomes. There is usually one nucleus, but there are also multinucleated cells.

Division into kingdoms

There are several options for dividing the eukaryotic superkingdom into kingdoms. The plant and animal kingdoms were the first to be distinguished. Then the kingdom of fungi was identified, which, due to their biochemical characteristics, according to most biologists, cannot be classified as one of these kingdoms. Also, some authors distinguish the kingdoms of protozoa, myxomycetes, and chromists. Some systems have up to 20 kingdoms. According to the Thomas Cavalier-Smith system, all eukaryotes are divided into two monophyletic taxa - Unikonta And Bikonta.

Differences between eukaryotes and prokaryotes

The most important, fundamental feature of eukaryotic cells is associated with the location of the genetic apparatus in the cell. The genetic apparatus of all eukaryotes is located in the nucleus and is protected by the nuclear envelope (in Greek, “eukaryote” means having a nucleus). The DNA of eukaryotes is linear (in prokaryotes, the DNA is circular and is located in a special region of the cell - the nucleoid, which is not separated by a membrane from the rest of the cytoplasm). It is associated with histone proteins and other chromosomal proteins that bacteria do not have.

In the life cycle of eukaryotes, there are usually two nuclear phases (haplophase and diplophase). The first phase is characterized by a haploid (single) set of chromosomes, then, merging, two haploid cells (or two nuclei) form a diploid cell (nucleus) containing a double (diploid) set of chromosomes. Sometimes during the next division, and more often after several divisions, the cell again becomes haploid. Such a life cycle and, in general, diploidity are not typical for prokaryotes.

The third, perhaps the most interesting difference, is the presence in eukaryotic cells of special organelles that have their own genetic apparatus, reproduce by division and are surrounded by a membrane. These organelles are mitochondria and plastids. In their structure and life activity they are strikingly similar to bacteria. This circumstance has prompted modern scientists to believe that such organisms are descendants of bacteria that entered into a symbiotic relationship with eukaryotes. Prokaryotes are characterized by a small number of organelles, and none of them are surrounded by a double membrane. Prokaryotic cells do not have an endoplasmic reticulum, Golgi apparatus, or lysosomes.

Another important difference between prokaryotes and eukaryotes is the presence of endocytosis in eukaryotes, including phagocytosis in many groups. Phagocytosis (literally “eating by a cell”) is the ability of eukaryotic cells to capture, enclose in a membrane vesicle, and digest a wide variety of solid particles. This process provides an important protective function in the body. It was first discovered by I.I. Mechnikov at the starfish. The appearance of phagocytosis in eukaryotes is most likely associated with average size (more about size differences is written below). The sizes of prokaryotic cells are disproportionately smaller, and therefore, in the process of evolutionary development of eukaryotes, they had the problem of supplying the body with a large amount of food. As a result, the first real, mobile predators appear among eukaryotes.

Most bacteria have a cell wall that is different from the eukaryotic one (not all eukaryotes have it). In prokaryotes, it is a durable structure consisting mainly of murein (in archaea, pseudomurein). The structure of murein is such that each cell is surrounded by a special mesh sac, which is one huge molecule. Among eukaryotes, many protists, fungi and plants have a cell wall. In fungi it consists of chitin and glucans, in lower plants it consists of cellulose and glycoproteins, diatoms synthesize a cell wall from silicic acids, in higher plants it consists of cellulose, hemicellulose and pectin. Apparently, for larger eukaryotic cells it has become impossible to create a cell wall of high strength from a single molecule. This circumstance could force eukaryotes to use different material for the cell wall. Another explanation is that the common ancestor of eukaryotes lost its cell wall due to the transition to predation, and then the genes responsible for the synthesis of murein were also lost. When some eukaryotes returned to osmotrophic nutrition, the cell wall appeared again, but on a different biochemical basis.

The metabolism of bacteria is also diverse. In general, there are four types of nutrition, and all are found among bacteria. These are photoautotrophic, photoheterotrophic, chemoautotrophic, chemoheterotrophic (phototrophic use the energy of sunlight, chemotrophic use chemical energy). Eukaryotes either synthesize energy from sunlight themselves or use ready-made energy of this origin. This may be due to the emergence of predators among eukaryotes, for which the need to synthesize energy has disappeared.

Another difference is the structure of the flagella. In bacteria they are thin - only 15-20 nm in diameter. These are hollow filaments made from the protein flagellin. The structure of eukaryotic flagella is much more complex. They are a cell outgrowth surrounded by a membrane and contain a cytoskeleton (axoneme) of nine pairs of peripheral microtubules and two microtubules in the center. Unlike rotating prokaryotic flagella, eukaryotic flagella bend or wriggle. The two groups of organisms we are considering, as already mentioned, are very different in their average sizes. The diameter of a prokaryotic cell is usually 0.5-10 microns, while the same figure for eukaryotes is 10-100 microns. The volume of such a cell is 1000-10000 times greater than that of a prokaryotic cell. Prokaryotes have small ribosomes (70S type). Eukaryotes have larger ribosomes (80S type).