The structure of eukaryotic and prokaryotic cells. Eukaryotic cell. The structure of a prokaryotic cell. Comparison of prokaryotic and eukaryotic cells.

There are two types of cells known in modern and fossil organisms: prokaryotic and eukaryotic. They differ so sharply in structural features that this served to distinguish two superkingdoms of the living world - prokaryotes, i.e. prenuclear, and eukaryotes, i.e. real nuclear organisms. Intermediate forms between these largest living taxa are still unknown.

Main features and differences between prokaryotic and eukaryotic cells (table):

Signs	Prokaryotes	Eukaryotes
NUCLEAR MEMBRANE	Absent	Available
PLASMA MEMBRANE	Available	Available
MITOCHONDRIA	None	Available
EPS	Absent	Available
RIBOSOMES	Available	Available
VACUOLES	None	Available (especially typical for plants)
LYSOSOMES	None	Available
CELL WALL	Available, consists of a complex heteropolymer substance	Absent in animal cells, in plant cells it consists of cellulose
CAPSULE	If present, it consists of protein and sugar compounds	Absent
GOLGI COMPLEX	Absent	Available
DIVISION	Simple	Mitosis, amitosis, meiosis

The main difference between prokaryotic cells and eukaryotic cells is that their DNA is not organized into chromosomes and is not surrounded by a nuclear envelope. Eukaryotic cells are much more complex. Their DNA, associated with protein, is organized into chromosomes, which are located in a special formation, essentially the largest organelle of the cell - the nucleus. In addition, the extranuclear active content of such a cell is divided into separate compartments using the endoplasmic reticulum formed by the elementary membrane. Eukaryotic cells are usually larger than prokaryotic cells. Their sizes vary from 10 to 100 microns, while the sizes of prokaryotic cells (various bacteria, cyanobacteria - blue-green algae and some other organisms), as a rule, do not exceed 10 microns, often amounting to 2-3 microns. In a eukaryotic cell, gene carriers - chromosomes - are located in a morphologically formed nucleus, delimited from the rest of the cell by a membrane. In exceptionally thin, transparent preparations, living chromosomes can be seen using a light microscope. More often they are studied on fixed and colored preparations.

Chromosomes consist of DNA, which is complexed with histone proteins rich in the amino acids arginine and lysine. Histones make up a significant portion of the mass of chromosomes.

A eukaryotic cell has a variety of permanent intracellular structures - organelles (organelles) that are absent in a prokaryotic cell.

Prokaryotic cells can divide into equal parts by constriction or bud, i.e. produce daughter cells smaller than the mother cell, but never divide by mitosis. In contrast, cells of eukaryotic organisms divide by mitosis (except for some very archaic groups). In this case, the chromosomes “split” longitudinally (more precisely, each DNA strand reproduces its own likeness around itself), and their “halves” - chromatids (full copies of the DNA strand) disperse in groups to opposite poles of the cell. Each of the resulting cells receives the same set of chromosomes.

The ribosomes of a prokaryotic cell differ sharply from the ribosomes of eukaryotes in size. A number of processes characteristic of the cytoplasm of many eukaryotic cells - phagocytosis, pinocytosis and cyclosis (rotational movement of the cytoplasm) - have not been found in prokaryotes. A prokaryotic cell does not require ascorbic acid in the metabolic process, but eukaryotic cells cannot do without it.

The motile forms of prokaryotic and eukaryotic cells differ significantly. Prokaryotes have motor devices in the form of flagella or cilia, consisting of the protein flagellin. The motor devices of motile eukaryotic cells are called undulipodia, which are anchored in the cell with the help of special kinetosome bodies. Electron microscopy revealed the structural similarity of all undulipodia of eukaryotic organisms and their sharp differences from the flagella of prokaryotes

1. The structure of a eukaryotic cell.

The cells that form the tissues of animals and plants vary significantly in shape, size and internal structure. However, they all show similarities in the main features of life processes, metabolism, irritability, growth, development, and the ability to change.
All types of cells contain two main components that are closely related to each other - the cytoplasm and the nucleus. The nucleus is separated from the cytoplasm by a porous membrane and contains nuclear sap, chromatin and the nucleolus. Semi-liquid cytoplasm fills the entire cell and is penetrated by numerous tubules. On the outside it is covered with a cytoplasmic membrane. It has specialized organelle structures, permanently present in the cell, and temporary formations - inclusions. Membrane organelles : outer cytoplasmic membrane (OCM), endoplasmic reticulum (ER), Golgi apparatus, lysosomes, mitochondria and plastids. The structure of all membrane organelles is based on a biological membrane. All membranes have a fundamentally uniform structural plan and consist of a double layer of phospholipids, into which protein molecules are immersed at different depths on different sides. The membranes of organelles differ from each other only in the sets of proteins they contain.

Cytoplasmic membrane. All plant cells, multicellular animals, protozoa and bacteria have a three-layer cell membrane: the outer and inner layers consist of protein molecules, the middle layer consists of lipid molecules. It limits the cytoplasm from the external environment, surrounds all cell organelles and is a universal biological structure. In some cells, the outer membrane is formed by several membranes tightly adjacent to each other. In such cases, the cell membrane becomes dense and elastic and allows the cell to maintain its shape, as, for example, in euglena and slipper ciliates. Most plant cells, in addition to the membrane, also have a thick cellulose shell on the outside - cell wall. It is clearly visible in a conventional light microscope and performs a supporting function due to the rigid outer layer, which gives the cells a clear shape.
On the surface of cells, the membrane forms elongated outgrowths - microvilli, folds, invaginations and protrusions, which greatly increases the absorption or excretory surface. With the help of membrane outgrowths, cells connect with each other in the tissues and organs of multicellular organisms; various enzymes involved in metabolism are located on the folds of the membranes. By delimiting the cell from the environment, the membrane regulates the direction of diffusion of substances and at the same time actively transports them into the cell (accumulation) or out (excretion). Due to these properties of the membrane, the concentration of potassium, calcium, magnesium, and phosphorus ions in the cytoplasm is higher, and the concentration of sodium and chlorine is lower than in the environment. Through the pores of the outer membrane, ions, water and small molecules of other substances penetrate into the cell from the external environment. Penetration of relatively large solid particles into the cell is carried out by phagocytosis(from the Greek “phago” - devour, “drink” - cell). In this case, the outer membrane at the point of contact with the particle bends into the cell, drawing the particle deep into the cytoplasm, where it undergoes enzymatic cleavage. Drops of liquid substances enter the cell in a similar way; their absorption is called pinocytosis(from the Greek “pino” - drink, “cytos” - cell). The outer cell membrane also performs other important biological functions.
Cytoplasm 85% consists of water, 10% of proteins, the rest of the volume is made up of lipids, carbohydrates, nucleic acids and mineral compounds; all these substances form a colloidal solution similar in consistency to glycerin. The colloidal substance of a cell, depending on its physiological state and the nature of the influence of the external environment, has the properties of both a liquid and an elastic, denser body. The cytoplasm is penetrated by channels of various shapes and sizes, which are called endoplasmic reticulum. Their walls are membranes that are in close contact with all organelles of the cell and together with them constitute a single functional and structural system for the metabolism and energy and movement of substances within the cell.

The walls of the tubules contain tiny grains called granules. ribosomes. This network of tubules is called granular. Ribosomes can be located scattered on the surface of the tubules or form complexes of five to seven or more ribosomes, called polysomes. Other tubules do not contain granules; they form a smooth endoplasmic reticulum. Enzymes involved in the synthesis of fats and carbohydrates are located on the walls.

The internal cavity of the tubules is filled with waste products of the cell. Intracellular tubules, forming a complex branching system, regulate the movement and concentration of substances, separate various molecules of organic substances and the stages of their synthesis. On the inner and outer surfaces of membranes rich in enzymes, proteins, fats and carbohydrates are synthesized, which are either used in metabolism, or accumulate in the cytoplasm as inclusions, or are excreted.

Ribosomes found in all types of cells - from bacteria to cells of multicellular organisms. These are round bodies consisting of ribonucleic acid (RNA) and proteins in almost equal proportions. They certainly contain magnesium, the presence of which maintains the structure of ribosomes. Ribosomes can be associated with the membranes of the endoplasmic reticulum, with the outer cell membrane, or lie free in the cytoplasm. They carry out protein synthesis. In addition to the cytoplasm, ribosomes are found in the cell nucleus. They are formed in the nucleolus and then enter the cytoplasm.

Golgi complex in plant cells it looks like individual bodies surrounded by membranes. In animal cells, this organelle is represented by cisterns, tubules and vesicles. Cell secretion products enter the membrane tubes of the Golgi complex from the tubules of the endoplasmic reticulum, where they are chemically rearranged, compacted, and then pass into the cytoplasm and are either used by the cell itself or removed from it. In the tanks of the Golgi complex, polysaccharides are synthesized and combined with proteins, resulting in the formation of glycoproteins.

Mitochondria- small rod-shaped bodies bounded by two membranes. Numerous folds - cristae - extend from the inner membrane of the mitochondrion; on their walls there are various enzymes, with the help of which the synthesis of a high-energy substance - adenosine triphosphoric acid (ATP) is carried out. Depending on the activity of the cell and external influences, mitochondria can move, change their size and shape. Ribosomes, phospholipids, RNA and DNA are found in mitochondria. The presence of DNA in mitochondria is associated with the ability of these organelles to reproduce by forming a constriction or budding during cell division, as well as the synthesis of some mitochondrial proteins.

Lysosomes- small oval formations, bounded by a membrane and scattered throughout the cytoplasm. Found in all cells of animals and plants. They arise in extensions of the endoplasmic reticulum and in the Golgi complex, here they are filled with hydrolytic enzymes, and then separate and enter the cytoplasm. Under normal conditions, lysosomes digest particles that enter the cell by phagocytosis and organelles of dying cells. Lysosome products are excreted through the lysosome membrane into the cytoplasm, where they are included in new molecules. When the lysosome membrane ruptures, enzymes enter the cytoplasm and digest its contents, causing cell death.
Plastids found only in plant cells and found in most green plants. Organic substances are synthesized and accumulated in plastids. There are three types of plastids: chloroplasts, chromoplasts and leucoplasts.

Chloroplasts - green plastids containing the green pigment chlorophyll. They are found in leaves, young stems, and unripe fruits. Chloroplasts are surrounded by a double membrane. In higher plants, the internal part of the chloroplasts is filled with a semi-liquid substance, in which the plates are laid parallel to each other. Paired membranes of the plates fuse to form stacks containing chlorophyll. In each stack of chloroplasts of higher plants, layers of protein molecules and lipid molecules alternate, and chlorophyll molecules are located between them. This layered structure provides maximum free surfaces and facilitates the capture and transfer of energy during photosynthesis.
Chromoplasts - plastids containing plant pigments (red or brown, yellow, orange). They are concentrated in the cytoplasm of cells of flowers, stems, fruits, and leaves of plants and give them the appropriate color. Chromoplasts are formed from leucoplasts or chloroplasts as a result of the accumulation of pigments carotenoids.

Leukoplasts—colorless plastids located in the uncolored parts of plants: in stems, roots, bulbs, etc. Starch grains accumulate in the leucoplasts of some cells, and oils and proteins accumulate in the leucoplasts of other cells.

All plastids arise from their predecessors, proplastids. They revealed DNA that controls the reproduction of these organelles.

Cell center, or centrosome, plays an important role in cell division and consists of two centrioles . It is found in all animal and plant cells, except for flowering fungi, lower fungi and some protozoa. Centrioles in dividing cells take part in the formation of the division spindle and are located at its poles. In a dividing cell, the cell center is the first to divide, and at the same time an achromatin spindle is formed, which orients the chromosomes as they diverge to the poles. One centriole leaves each of the daughter cells.
Many plant and animal cells have special purpose organoids: cilia, performing the function of movement (ciliates, respiratory tract cells), flagella(protozoa unicellular, male reproductive cells in animals and plants, etc.).

Inclusions - temporary elements that arise in a cell at a certain stage of its life as a result of a synthetic function. They are either used or removed from the cell. Inclusions are also reserve nutrients: in plant cells - starch, droplets of fat, proteins, essential oils, many organic acids, salts of organic and inorganic acids; in animal cells - glycogen (in liver cells and muscles), drops of fat (in subcutaneous tissue); Some inclusions accumulate in cells as waste - in the form of crystals, pigments, etc.

Vacuoles - these are cavities bounded by a membrane; well expressed in plant cells and present in protozoa. They arise in different areas of the endoplasmic reticulum. And they gradually separate from it. Vacuoles maintain turgor pressure; cellular or vacuolar sap is concentrated in them, the molecules of which determine its osmotic concentration. It is believed that the initial products of synthesis - soluble carbohydrates, proteins, pectins, etc. - accumulate in the cisterns of the endoplasmic reticulum. These clusters represent the rudiments of future vacuoles.
Cytoskeleton . One of the distinctive features of a eukaryotic cell is the development in its cytoplasm of skeletal formations in the form of microtubules and bundles of protein fibers. The elements of the cytoskeleton are closely associated with the outer cytoplasmic membrane and the nuclear envelope and form complex weaves in the cytoplasm. The supporting elements of the cytoplasm determine the shape of the cell, ensure the movement of intracellular structures and the movement of the entire cell.

Core The cell plays a major role in its life; with its removal, the cell ceases its functions and dies. Most animal cells have one nucleus, but there are also multinucleated cells (human liver and muscles, fungi, ciliates, green algae). Mammalian red blood cells develop from precursor cells containing a nucleus, but mature red blood cells lose it and do not live long.
The nucleus is surrounded by a double membrane, permeated with pores, through which it is closely connected with the channels of the endoplasmic reticulum and the cytoplasm. Inside the core is chromatin- spiralized sections of chromosomes. During cell division, they turn into rod-shaped structures that are clearly visible under a light microscope. Chromosomes are complex complexes of proteins and DNA called nucleoprotein.

The functions of the nucleus are to regulate all the vital functions of the cell, which it carries out with the help of DNA and RNA material carriers of hereditary information. In preparation for cell division, DNA doubles; during mitosis, chromosomes separate and are passed on to daughter cells, ensuring the continuity of hereditary information in each type of organism.

Karyoplasm - the liquid phase of the nucleus, in which the waste products of nuclear structures are found in dissolved form.

Nucleolus- isolated, densest part of the core.

The nucleolus contains complex proteins and RNA, free or bound phosphates of potassium, magnesium, calcium, iron, zinc, as well as ribosomes. The nucleolus disappears before the start of cell division and is re-formed in the last phase of division.

Thus, the cell has a fine and very complex organization. The extensive network of cytoplasmic membranes and the membrane principle of the structure of organelles make it possible to distinguish between the many chemical reactions occurring simultaneously in the cell. Each of the intracellular formations has its own structure and specific function, but only through their interaction is the harmonious functioning of the cell possible. Based on this interaction, substances from the environment enter the cell, and waste products are removed from it into the external environment - this is how metabolism occurs. The perfection of the structural organization of a cell could only arise as a result of long-term biological evolution, during which the functions it performed gradually became more complex.
The simplest unicellular forms represent both a cell and an organism with all its life manifestations. In multicellular organisms, cells form homogeneous groups - tissues. In turn, tissues form organs, systems, and their functions are determined by the general vital activity of the whole organism.

2. Prokaryotic cell.

Prokaryotes include bacteria and blue-green algae (cyanea). The hereditary apparatus of prokaryotes is represented by one circular DNA molecule that does not form bonds with proteins and contains one copy of each gene - haploid organisms. The cytoplasm contains a large number of small ribosomes; internal membranes are absent or poorly expressed. Enzymes of plastic metabolism are located diffusely. The Golgi apparatus is represented by individual vesicles. Enzyme systems for energy metabolism are orderedly located on the inner surface of the outer cytoplasmic membrane. The outside of the cell is surrounded by a thick cell wall. Many prokaryotes are capable of sporulation under unfavorable living conditions; in this case, a small section of the cytoplasm containing DNA is isolated and surrounded by a thick multilayer capsule. Metabolic processes inside the spore practically stop. When exposed to favorable conditions, the spore transforms into an active cellular form. Prokaryotes reproduce by simple division in two.

The average size of prokaryotic cells is 5 microns. They do not have any internal membranes other than invaginations of the plasma membrane. There are no layers. Instead of a cell nucleus, there is its equivalent (nucleoid), devoid of a shell and consisting of a single DNA molecule. In addition, bacteria may contain DNA in the form of tiny plasmids, similar to the extranuclear DNA of eukaryotes.
Prokaryotic cells capable of photosynthesis (blue-green algae, green and purple bacteria) have differently structured large membrane invaginations - thylakoids, which in their function correspond to eukaryotic plastids. These same thylakoids or, in colorless cells, smaller membrane invaginations (and sometimes even the plasma membrane itself) functionally replace mitochondria. Other, complexly differentiated membrane invaginations are called mesasomes; their function is not clear.
Only some organelles of a prokaryotic cell are homologous to the corresponding organelles of eukaryotes. Prokaryotes are characterized by the presence of a murein sac - a mechanically strong element of the cell wall

Comparative characteristics of cells of plants, animals, bacteria, fungi

When comparing bacteria with eukaryotes, the only similarity that can be identified is the presence of a cell wall, but the similarities and differences of eukaryotic organisms deserve closer attention. The comparison should begin with components that are characteristic of plants, animals, and fungi. These are the nucleus, mitochondria, Golgi apparatus (complex), endoplasmic reticulum (or endoplasmic reticulum) and lysosomes. They are characteristic of all organisms, have a similar structure and perform the same functions. Now we need to focus on the differences. A plant cell, unlike an animal cell, has a cell wall consisting of cellulose. In addition, there are organelles characteristic of plant cells - plastids and vacuoles. The presence of these components is due to the need for plants to maintain their shape in the absence of a skeleton. There are differences in growth characteristics. In plants, it occurs mainly due to an increase in the size of vacuoles and cell elongation, while in animals there is an increase in the volume of the cytoplasm, and the vacuole is completely absent. Plastids (chloroplasts, leucoplasts, chromoplasts) are characteristic primarily of plants, since their main task is to provide an autotrophic method of nutrition. Animals, as opposed to plants, have digestive vacuoles that provide a heterotrophic method of nutrition. Fungi occupy a special position and their cells are characterized by characteristics characteristic of both plants and animals. Like animal fungi, they have a heterotrophic type of nutrition, a chitin-containing cell wall, and the main storage substance is glycogen. At the same time, they, like plants, are characterized by unlimited growth, inability to move, and nutrition by absorption.

All living organisms on earth are made up of cells. There are two types of cells, depending on their organization: eukaryotes and prokaryotes.

Eukaryotes represent the superkingdom of living organisms. Translated from Greek, “eukaryote” means “possessing a nucleus.” Accordingly, these organisms have a core in which all genetic information is encoded. These include fungi, plants and animals.

Prokaryotes- These are living organisms whose cells do not have a nucleus. Typical representatives of prokaryotes are bacteria and cyanobacteria.

Time of occurrence

The first prokaryotes arose approximately 3.5 billion years ago, which 2.4 billion years later marked the beginning of the development of eukaryotic cells.

Size

Eukaryotes and prokaryotes differ greatly in size from each other. So the diameter of a eukaryotic cell is 0.01-0.1 mm, and that of a prokaryotic cell is 0.0005-0.01 mm. The volume of a eukaryote is about 10,000 times greater than that of a prokaryote.

DNA

Prokaryotes have circular DNA, which is located in the nucleoid. This cellular region is separated from the rest of the cytoplasm by a membrane. DNA is not connected in any way to RNA and proteins; there are no chromosomes.

The DNA of eukaryotic cells is linear and is located in the nucleus, which contains chromosomes.

Cell division of eukaryotes and prokaryotes

Prokaryotes reproduce primarily by simple fission, while eukaryotes divide by mitosis, meiosis, or a combination of the two.

Organelles

Eukaryotic cells have organelles characterized by the presence of their own genetic apparatus: mitochondria and plastids. They are surrounded by a membrane and have the ability to reproduce through division.

Organelles are also found in prokaryotic cells, but in smaller numbers and not limited to a membrane.

Phagocytosis

Eukaryotes, unlike prokaryotes, have the ability to digest solid particles by enclosing them in a membrane vesicle. There is an opinion that this feature arose in response to the need to fully provide nutrition to a cell many times larger than a prokaryotic one. A consequence of the presence of phagocytosis in eukaryotes was the appearance of the first predators.

Motor devices

Eukaryotic flagella have a rather complex structure. They are thin cellular projections surrounded by three layers of membrane, containing 9 pairs of microtubules at the periphery and two in the center. They have a thickness of up to 0.1 millimeters and are capable of bending along the entire length. In addition to flagella, eukaryotes are characterized by the presence of cilia. They are identical in structure to flagella, differing only in size. The length of the cilia is no more than 0.01 millimeters.

Some prokaryotes also have flagella, however, they are very thin, about 20 nanometers in diameter. They are passively rotating hollow protein filaments.

Conclusions website

1. Eukaryotes are mainly multicellular organisms that reproduce by. Prokaryotes are single-celled and reproduce by dividing into two.
2. Prokaryotic DNA is free in the cytoplasm and has the shape of a ring. Eukaryotes have a nucleus where linear DNA is located.
3. The size of a eukaryotic cell significantly exceeds the size of a prokaryotic cell, while eukaryotes are characterized by the presence of phagocytosis, which contributes to sufficient nutrition of the cell.

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 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.

Structure of eukaryotes

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.

Structure of eukaryotes

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.

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;

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 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).

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.