Who are eukaryotes and prokaryotes: comparative characteristics of cells of different kingdoms. Eukaryotes Who are eukaryotes

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 bubbles 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 appearance of eukaryotes is a major event. It changed the structure of the biosphere and opened up fundamentally new opportunities for progressive evolution. The eukaryotic cell is the result of a long evolution of the prokaryotic world, a world in which diverse microbes adapted to each other and sought ways to cooperate effectively.

sketch of chronology (repetition)

Photosynthetic prokaryotic complex Chlorochromatium aggregatum.

Eukaryotes arose as a result of the symbiosis of several types of prokaryotes. Prokaryotes are generally very prone to symbiosis (see Chapter 3 in the book “The Birth of Complexity”). Here is an interesting symbiotic system known as Chlorochromatium aggregatum. Lives in deep lakes where there are oxygen-free conditions at depth. The central component is a mobile heterotrophic betaproteobacterium. Around it there are stacks of 10 to 60 photosynthetic green sulfur bacteria. All components are connected by extensions of the outer membrane of the central bacterium. The point of the partnership is that the mobile betaproteobacteria drags the entire company to places favorable for the life of fastidious sulfur bacteria, and the sulfur bacteria engage in photosynthesis and provide food for both themselves and the betaproteobacteria. Perhaps some ancient microbial associations of approximately this type were the ancestors of eukaryotes.

Theory of symbiogenesis. Merezhkovsky, Margulis. Mitochondria are descendants of alpha-proteobacteria, plastids are descendants of cyanobacteria. It is more difficult to understand who was the ancestor of everything else, that is, the cytoplasm and the nucleus. The nucleus and cytoplasm of eukaryotes combines the characteristics of archaea and bacteria, and also has many unique features.

About mitochondria. Perhaps it was the acquisition of mitochondria (and not the nucleus) that was the key moment in the formation of eukaryotes. Most of the ancestral mitochondrial genes were transferred to the nucleus, where they came under the control of nuclear regulatory systems. These nuclear genes of mitochondrial origin encode not only mitochondrial proteins, but also many proteins that function in the cytoplasm. This suggests that the mitochondrial symbiont played a more important role in the formation of the eukaryotic cell than expected.

The coexistence of two different genomes in one cell required the development of an effective system for their regulation. And in order to effectively manage the work of a large genome, it is necessary to isolate the genome from the cytoplasm, in which metabolism takes place and thousands of chemical reactions take place. The nuclear envelope is what separates the genome from the violent chemical processes of the cytoplasm. The acquisition of symbionts (mitochondria) could become an important stimulus in the development of the nucleus and gene regulatory systems.

The same applies to sexual reproduction. You can live without sexual reproduction as long as your genome is small enough. Organisms with a large genome, but lacking sexual reproduction, are doomed to rapid extinction, with rare exceptions.

Alphaproteobacteria - the ancestors of mitochondria belonged to this group.

Rhodospirillum is an amazing microorganism that can live through photosynthesis, including under anaerobic conditions, and as an aerobic heterotroph, and even as an aerobic chemoautotroph. It can, for example, grow due to the oxidation of carbon monoxide CO, without using any other energy sources. In addition to all this, it can also fix atmospheric nitrogen. That is, it is a highly versatile organism.

The immune system mistakes mitochondria for bacteria. When damaged mitochondria enter the blood during injury, characteristic molecules are released from them that are found only in bacteria and mitochondria (circular DNA of the bacterial type and proteins carrying a special modified amino acid formylmethionine at one of their ends). This is due to the fact that the protein synthesis apparatus in mitochondria remains the same as in bacteria. The cells of the immune system - neutrophils - react to these mitochondrial substances in the same way as to bacterial ones, and using the same receptors. This is the clearest confirmation of the bacterial nature of mitochondria.

The main function of mitochondria is oxygen respiration. Most likely, the stimulus for combining the anaerobic ancestor of the nucleus and cytoplasm with the “protomitochondria” was the need to protect itself from the toxic effects of oxygen.

Where did bacteria, including alphaproteobacteria, get the molecular systems necessary for oxygen respiration? They appear to have been based on molecular systems of photosynthesis. The electron transport chain, formed in bacteria as part of the photosynthetic apparatus, was adapted for oxygen respiration. In some bacteria, sections of electron transport chains are still used simultaneously in photosynthesis and respiration. Most likely, the ancestors of mitochondria were aerobic heterotrophic alpha-proteobacteria, which, in turn, descended from photosynthetic alpha-proteobacteria such as Rhodospirillum.

Number of common and unique protein domains in archaea, bacteria and eukaryotes. A protein domain is a part of a protein molecule that has a specific function and characteristic structure, that is, a sequence of amino acids. Each protein, as a rule, contains one or more such structural and functional blocks, or domains.

The 4.5 thousand protein domains that eukaryotes have can be divided into 4 groups: 1) present only in eukaryotes, 2) common to all three superkingdoms, 3) common to eukaryotes and bacteria, but absent in archaea; 4) common to eukaryotes and archaea, but absent in bacteria. We will consider the last two groups (they are highlighted in color in the figure), since for these proteins we can speak with some confidence about their origin: bacterial or archaeal, respectively.

The key point is that the eukaryotic domains presumably inherited from bacteria and those from archaea have significantly different functions. Domains inherited from archaea (their functional spectrum is shown in the left graph) play a key role in the life of a eukaryotic cell. Among them, domains associated with the storage, reproduction, organization and reading of genetic information predominate. Most “archaeal” domains belong to those functional groups within which horizontal gene exchange in prokaryotes occurs least frequently. Apparently, eukaryotes received this complex through direct (vertical) inheritance from archaea.

Among the domains of bacterial origin there are also proteins associated with information processes, but they are few. Most of them work only in mitochondria or plastids. Eukaryotic ribosomes in the cytoplasm are of archaeal origin, while ribosomes in mitochondria and plastids are of bacterial origin.

Among the bacterial domains of eukaryotes, the proportion of signal-regulatory proteins is significantly higher. From bacteria, eukaryotes have inherited many proteins responsible for the mechanisms of cell response to environmental factors. And also many proteins associated with metabolism (for more details, see Chapter 3, “The Birth of Complexity”).

Eukaryotes have:

Archaeal “core” (mechanisms for working with genetic information and protein synthesis)

· Bacterial “periphery” (metabolism and signal-regulatory systems)

· The simplest scenario: ARCHEA swallowed BACTERIA (ancestors of mitochondria and plastids) and acquired all its bacterial characteristics from them.

· This scenario is too simple because eukaryotes have many bacterial proteins that could not have been borrowed from the ancestors of mitochondria or plastids.

Eukaryotes have many “bacterial” domains that are not characteristic of either cyanobacteria (the ancestors of plastids) or alphaproteobacteria (the ancestors of mitochondria). They were obtained from some other bacteria.

Birds and dinosaurs. Reconstructing proto-eukaryotes is difficult. It is clear that the group of ancient prokaryotes that gave rise to the nucleus and cytoplasm had a number of unique features that prokaryotes that have survived to this day do not have. And when we try to reconstruct the appearance of this ancestor, we are faced with the fact that the scope for hypotheses turns out to be too large.

Analogy. It is known that birds descended from dinosaurs, and not from some unknown dinosaurs, but from a very specific group - maniraptor dinosaurs, which belong to theropods, and theropods, in turn, are one of the groups of lizard-hipped dinosaurs. Many transitional forms between flightless dinosaurs and birds have been found.

But what could we say about the ancestors of birds if there were no fossil record? At best, we would find out that the closest relatives of birds are crocodiles. But could we recreate the appearance of the direct ancestors of birds, that is, dinosaurs? Hardly. But this is exactly the situation we find ourselves in when we try to restore the appearance of the ancestor of the nucleus and cytoplasm. It is clear that this was a group of some prokaryotic dinosaurs, a group that became extinct and, unlike real dinosaurs, did not leave clear traces in the geological record. Modern archaea are to eukaryotes what modern crocodiles are to birds. Try to reconstruct the structure of dinosaurs, knowing only birds and crocodiles.

An argument in favor of the fact that in the Precambrian there lived many different microbes that were not similar to those of today. Proterozoic stromatolites were much more complex and diverse than modern ones. Stromatolites are a product of the vital activity of microbial communities. Doesn't this mean that Proterozoic microbes were more diverse than modern ones, and that many groups of Proterozoic microbes simply did not survive to this day?

The ancestral community of eukaryotes and the origin of the eukaryotic cell (possible scenario)

The hypothetical “ancestral community” is a typical bacterial mat, only in its upper one lived the ancestors of cyanobacteria, which had not yet transferred to oxygenic photosynthesis. They were engaged in anoxygenic photosynthesis. The electron donor was not water, but hydrogen sulfide. Sulfur and sulfates were released as by-products.

The second layer was inhabited by purple photosynthetic bacteria, including alphaproteobacteria, the ancestors of mitochondria. Purple bacteria use long-wavelength light (red and infrared). These waves have better penetrating power. Purple bacteria still often live under a layer of cyanobacteria. Purple alphaproteobacteria also use hydrogen sulfide as an electron donor.

The third layer contained fermenting bacteria that processed organic matter; some of them released hydrogen as waste. This created a base for sulfate-reducing bacteria. There could also be methanogenic archaea. Among the archaea that lived here were the ancestors of the nucleus and cytoplasm.

The crisis events began with the transition of cyanobacteria to oxygen photosynthesis. Cyanobacteria began to use ordinary water instead of hydrogen sulfide as an electron donor. This opened up great opportunities, but also had negative consequences. Instead of sulfur and sulfates, oxygen began to be released during photosynthesis - a substance extremely toxic to all ancient inhabitants of the earth.

The first to encounter this poison were its producers – cyanobacteria. They were probably the first to develop means of protection against it. The electron transport chains that served for photosynthesis were modified and began to serve for aerobic respiration. The original purpose, apparently, was not to obtain energy, but only to neutralize oxygen.

Soon, the inhabitants of the second layer of the community - purple bacteria - had to develop similar defense systems. Just like cyanobacteria, they formed aerobic respiration systems based on photosynthetic systems. It was the purple alphaproteobacteria that developed the most advanced respiratory chain, which now functions in the mitochondria of eukaryotes.

In the third layer of the community, the appearance of free oxygen should have caused a crisis. Methanogens and many sulfate reducers utilize molecular hydrogen using hydrogenase enzymes. Such microbes cannot live under aerobic conditions because oxygen inhibits hydrogenases. Many bacteria that produce hydrogen, in turn, do not grow in an environment where there are no microorganisms that utilize it. Of the fermenters in the community, apparently, there remained forms that secrete low-organic compounds (pyruvate, lactate, acetate, etc.) as final products. These fermenters have developed their own means of protecting themselves from oxygen, which are less effective. Among the survivors were archaea - the ancestors of the nucleus and cytoplasm.

Perhaps, at this moment of crisis, a key event occurred - the weakening of genetic isolation in the ancestors of eukaryotes and the beginning of active borrowing of foreign genes. Proto-eukaryotes incorporated the genes of various fermenters until they themselves became microaerophilic fermenters, fermenting carbohydrates into pyruvate and lactic acid.

The inhabitants of the third layer - the ancestors of eukaryotes - were now in direct contact with the new inhabitants of the second layer - aerobic alphaproteobacteria, which had learned to use oxygen to produce energy. The metabolism of proto-eukaryotes and alphaproteobacteria became complementary, which created the preconditions for symbiosis. And the very location of alphaproteobacteria in the community (between the upper, oxygen-producing layer and the lower layer) predetermined their role as “protectors” of the ancestors of eukaryotes from excess oxygen.

Proto-eukaryotes probably ingested and acquired many different bacteria as endosymbionts. Experimentation of this kind continues today in unicellular eukaryotes, which have a huge variety of intracellular symbionts. Of these experiments, the alliance with aerobic alphaproteobacteria proved to be the most successful.

All organisms on our planet are made up of cells. Cells are usually divided into eukaryotes and prokaryotes.

Eukaryotes

First you need to define what eukaryotes are. If we translate this term from Greek, then it is translated as possessing the core. The nucleus of such organisms contains the genetic code. Such organisms include plants, fungi and animals.

The structure of a eukaryotic cell varies among different organisms. The eukaryotic cell has a rather complex structure. All eukaryotic cells consist of a nucleus and cytoplasm.

The eukaryotic cell has a membrane called the plasmalemma. It protects the cell by selectively allowing certain substances to enter the cell. The cytoplasm is adjacent to it from the inside. Various substances are stored in the cytoplasm. The cell has an endoplasmic reticulum, which facilitates the circulation of substances throughout the cell, as well as their transfer from one cell to another. Ribosomes, which are also found in the cell, are responsible for the synthesis of proteins. In addition, the cell may contain the Golgi complex, mitochondria, lysosomes, and centrioles. The cell nucleus contains DNA and is responsible for metabolism. It is covered with a special shell, with the help of which metabolism occurs between the nucleus and the cytoplasm.

Having examined the structure of eukaryotes, it becomes clear what eukaryotes are and that they cannot exist without a nucleus. Eukaryotic cells are mononucleate and multinucleate. The nucleus can have a variety of shapes, which depends on the shape of the cell itself.

How do eukaryotes and prokaryotes differ?

Prokaryotes are organisms found in cells that lack a nucleus. The absence of a nucleus is the main way prokaryotes differ from eukaryotes. Prokaryotes include, for example, bacteria.

Eukaryotes and prokaryotes also differ in size and volume. Eukaryotes are much larger in size than prokaryotes. Eukaryotes are usually multicellular organisms, while prokaryotes are unicellular. Prokaryotes reproduce by simply dividing the cell in half, while eukaryotes have a more complex reproduction mechanism. The DNA of eukaryotes is located in the nucleus, and that of prokaryotes in the cytoplasm.

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.

In contact with

Signs of a prokaryotic cell

Prokaryotes are also called prenuclear. A prokaryotic cell does not have other organelles that have a membrane membrane (endoplasmic reticulum, Golgi complex).

Also characteristic of 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 form spores under unfavorable conditions.
5. The presence of plasmids - small extrachromosomal DNA molecules. Their function is the transfer of 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 of prokaryotes (namely 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, crenarchaeotes.

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.

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 with Gram, they give a violet color. Most of these bacteria are pathogens. Gram-negatives 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 required level of oxygen in the atmosphere. They form more than half of all O2 on Earth.
2. They promote the decomposition of organic remains, thereby taking part in the cycle of all substances, and participate in the formation of soil.
3. Nitrogen fixers on legume roots.
4. They purify water from waste, for example, from the metallurgical industry.
5. They are part of the microflora of living organisms, helping to maximize the absorption of nutrients.
6. Used in the food industry for fermentation. This is how cheeses, cottage cheese, alcohol, and dough are produced.

Attention! In addition to their positive significance, bacteria also play a negative role. Many of them cause deadly diseases, such as cholera, typhoid fever, syphilis, and tuberculosis.

Bacteria

Archaea

Previously, they were combined with bacteria into the single kingdom of Drobyanok. However, over time, it became clear that archaea have their own individual path of evolution and are very different from other microorganisms in their biochemical composition and metabolism.

• There are up to 5 types, the most studied are euryarchaeota and crenarchaeota. The features of archaea 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 high temperatures;

the cell wall, unlike bacteria, does not contain peptidoglycan and consists of pseudomurein.

Eukaryotes are a superkingdom of organisms whose cells contain a nucleus. Apart from 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 functions. 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-membranous organelles. Membranous ones include: endoplasmic reticulum, lysosomes, Golgi complex, mitochondria,. Non-membrane: ribosomes, cell center, microtubules, microfilaments.

the cell wall, unlike bacteria, does not contain peptidoglycan and consists of pseudomurein.

Let's compare eukaryotic cells from different kingdoms.

The superkingdom of eukaryotes includes the following kingdoms:

• protozoa. Heterotrophs, some capable of photosynthesis (algae). They reproduce asexually, sexually and in a simple way into two parts. Most lack a cell wall;
• plants. They are producers; the main method of obtaining energy is photosynthesis. Most plants are immobile and reproduce asexually, sexually and vegetatively. The cell wall is made of cellulose;
• mushrooms. Multicellular. There are lower and higher. They are heterotrophic organisms and cannot move independently. They reproduce asexually, sexually and vegetatively. They store glycogen and have a strong cell wall made of 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 consists of chitin, just like in fungi. The main method of reproduction is sexual.

Table: Comparative characteristics of plant and animal cells

Structure	plant cell	animal cell
Cell wall	Cellulose	Consists of the glycocalyx - a thin layer of proteins, carbohydrates and lipids.
Core location	Located closer to the wall	Located in the central part
Cell center	Exclusively in lower algae	Present
Vacuoles	Contains cell sap	Contractile and digestive.
Spare substance	Starch	Glycogen
Plastids	Three types: chloroplasts, chromoplasts, leucoplasts	None
Nutrition	Autotrophic	Heterotrophic

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 method of obtaining energy.

Prokaryotes and eukaryotes photosynthesize differently. In prokaryotes, this process takes place on membrane outgrowths (chromatophores), arranged in separate stacks. Bacteria do not have a fluorine photosystem, so they do not produce oxygen, unlike blue-green algae, which produce 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 arranged in grana or lamellae. The presence of photosystem II allows the release of oxygen into the atmosphere during the process of photolysis of water. The only source of hydrogen molecules is water. The main pigment is chlorophyll, and phycobilins are present only in red algae.

The main differences and characteristic features of prokaryotes and eukaryotes are presented in the table below.

Table: Similarities and differences between prokaryotes and eukaryotes

Comparison	Prokaryotes	Eukaryotes
Appearance time	More than 3.5 billion years	About 1.2 billion years
Cell sizes	Up to 10 microns	From 10 to 100 µm
Capsule	Eat. Performs a protective function. Associated with the cell wall	Absent
Plasma membrane	Eat	Eat
Cell wall	Composed of pectin or murein	Yes, except animals
Chromosomes	Instead there is circular DNA. Translation and transcription take place in the cytoplasm.	Linear DNA molecules. Translation takes place in the cytoplasm, and transcription in the nucleus.
Ribosomes	Small 70S-type. Located in the cytoplasm.	Large 80S-type, can attach to the endoplasmic reticulum and be located in plastids and mitochondria.
Membrane-enclosed organoid	None. There are membrane outgrowths - mesosomes	There are: mitochondria, Golgi complex, cell center, ER
Cytoplasm	Eat	Eat
	None	Eat
Vacuoles	Gas (aerosomes)	Eat
Chloroplasts	None. Photosynthesis takes place in bacteriochlorophylls	Present only in plants
Plasmids	Eat	None
Core	Absent	Eat
Microfilaments and microtubules.	None	Eat
Division methods	Constriction, budding, conjugation	Mitosis, meiosis
Interaction or contacts	None	Plasmodesmata, desmosomes or septa
Types of cell nutrition	Photoautotrophic, photoheterotrophic, chemoautotrophic, chemoheterotrophic	Phototrophic (in plants) endocytosis and phagocytosis (in others)

Differences between prokaryotes and eukaryotes

Similarities and differences between prokaryotic and eukaryotic cells

Conclusion

Comparing a prokaryotic and eukaryotic organism is a rather labor-intensive 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, methods of nutrition and internal organization. Anyone interested in this topic can use this information.

Bacteria are prenuclear unicellular microorganisms, prokaryotes, that is, they do not have a nuclear protein shell - packaging for DNA. Also, their structure is more simplified compared to animal and plant cells. The main type of nutrition is photosynthesis (using light energy) or chemosynthesis (oxidation of substances). Prokaryotes also include archaea and blue-green algae.

Eukaryotes are a superkingdom of living organisms whose cells have a nucleus and its shell is clearly defined. The term is translated from Greek as “good core,” which is why this name was chosen.

This superkingdom includes plants, animals, fungi, protozoa, fungus-like organisms, slime molds, and algae.

There is a theory that an ancient cyanobacterium about 2.5 billion years ago was captured by a cell - the predecessor of a eukaryote, which led to the emergence of completely new microorganisms. Some individual organelles of eukaryotes (for example, mitochondria and plastids) are very similar to bacteria in structure and characteristics of life. They also reproduce by division and have their own genetic apparatus.

The main difference between eukaryotes and bacteria (prokaryotes) and archaea is the location of the genetic apparatus surrounded by a double membrane, protected by a strong nuclear shell. There are multinucleate organisms. They have linear DNA associated with histones - proteins in which the threads are packaged. In bacteria, the DNA is circular and not bound by histones.

The cell has dozens of permanent structures - its organelles that provide vital functions, each of which is separated by one or more membranes. This is quite rare in prokaryotes.

The presence of plastids, which can consist of 4 membranes, also significantly distinguishes prokaryotes from eukaryotes. Plastids are surrounded by an outer and inner membrane and perform:

• functions of photosynthesis,
• synthesis of amino acids, purines, abscisic acid and other important compounds.

Plastids provide reserves of lipids, starch, and iron.

Eukaryotes are thousands of times larger than prokaryotes. This is why they need to consume large amounts of protein as food to stay alive. This led to the emergence of predatory organisms.

Structural features

A standard cell consists of the following structures:

• core,
• ribosome,
• vesicle,
• rough endoplasmic reticulum,
• Golgi apparatus,
• smooth endoplasmic reticulum,
• mitochondria,
• vacuole,
• hyaloplasm,
• lysosome,
• centrosome,
• melanosome,
• cilia, flagella,
• cell wall.

The nucleus contains a nucleolus, which does not have a membrane. It is clearly visible under an electron microscope. RNA synthesis occurs in the nucleolus. The nucleus ensures the storage of DNA - hereditary information, its transmission, implementation, and reproduction.

Ribosome, being an organelle, has the shape of a sphere, carries out translation (protein synthesis from amino acids). Ribosomes are big and small.

Structure of a eukaryotic cell

A vesicle is a small organelle separated by a membrane that forms an intracellular bag for transporting or converting nutrients and storing enzymes.

Rough (granular) endoplasmic reticulum consists of branches, characterized by the presence of bubbles, tubes and cavities. It is surrounded by a membrane shell. Its surface contains ribosomes that carry out protein synthesis.

The Golgi apparatus is a structure consisting of membranes and “cisterns” that help remove substances from the granular endoplasmic reticulum. In appearance it resembles tubes collected in stacks. The maturation of proteins occurs in the tanks; each section contains its own set of enzymes. Vesicles, separating from the reticulum, are continuously attached to the Golgi apparatus. When the protein is ready to move, the vesicles detach and are delivered to the desired organelle. The Golgi apparatus sorts substances, sending some of them to the plasma membrane, others to lysosomes.

Smooth (agranular) endoplasmic reticulum has no ribosomes. Responsible for metabolic processes. Carries out the synthesis of lipids, fatty acids, steroids. The tissues of the liver and adrenal glands consist of smooth endoplasmic reticulum.

Mitochondria are organelles that oxidize organic compounds, using energy to ensure the life of the entire organism. May vary in form, the number contained in one cell can vary from one mitochondria to hundreds of thousands. It contains a circular helical DNA molecule.

Vacuoles develop from membrane vesicles. Not all eukaryotes have them. They perform the function of accumulating water and removing decay products. They are digestive and pulsating.

Hyaloplasm is an intracellular fluid.

A lysosome is an organelle, a type of vesicle surrounded by a membrane, containing enzymes. Performs the function of digesting molecules through secretion. Prokaryotes do not have lysosomes.

The centrosome regulates the processes of cell division and tube formation, being a non-membrane organelle. Participates in the formation of flagella and cilia.

Melanosome is present in animals and contains light-absorbing pigments, in particular melanin.

Cilia are thin hairs on the surface of the cell wall, covered with a membrane, which are receptors. They are found in ciliates, sponges, and ciliated worms. They are found in intestinal epithelial cells, respiratory tracts - bronchi, cerebral ventricles, and Eustachian tube.

Prokaryotes can also have flagella. In bacteria they are much thinner, shorter, and cannot bend. Eukaryotic flagella are longer than cilia, although they are similar in structure. In archaebacteria, the flagella are somewhat thinner and differ in structure.

Cell wall, first of all, provides protection of all internal structures from external factors, and also transports substances. It consists of murein, the structure of which affects the degree of Gram staining. Some bacteria, algae, fungi, and archaea also have a cell wall. Bacteria can also form a capsule - a mucous structure of polysaccharides, a large amount of water around the wall.

Life and nutrition of eukaryotes

The life cycle of eukaryotes is divided into two subsequent phases:

• haplophase,
• diplophase.

There is a fusion of two haloploid (with one set of chromosomes) cells and their nuclei into one common one, which has two (diploid) sets of chromosomes. After some time, the cells again become haloploid, dividing. This method is completely uncharacteristic of prokaryotes.

The difference between bacteria, archaea and eukaryotes is the ability of the latter to endocytosis - capturing other cells and placing them in special bags (vesicles), in which, through fermentation, food is “digested” to a consistency that can penetrate the cell membrane.

Some are capable of phagocytosis (from Greek “devouring”). They can capture solid particles (viruses, bacteria), digest them, thus providing nutrition.

Eukaryotes are also able to absorb liquid. Pinocytosis is the ability of all eukaryotic cells to absorb molecules of water and other liquid substances, satisfying their need to drink.

Structural features, differences in the processes responsible for the life of cells, as well as size, the presence of organs that perform certain functions - all this significantly distinguishes eukaryotes from bacteria. This is why they are not bacteria, but a separate type of microorganism.

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