Bacteria belong to prenuclear unicellular microorganisms prokaryotes, that is, they do not have a nuclear protein membrane - a packaging for DNA. Also, their structure is more simplified in comparison with the cells of animals and plants. The main type of nutrition is photosynthesis (using light energy) or chemosynthesis (oxidation of substances). Archaea, blue-green algae, also belong to prokaryotes.

Eukaryotes are a super-kingdom of living organisms, whose cells have a nucleus, and its shell is clearly formed. The term is translated from Greek as "good core", which is why this name was chosen.

Plants, animals, fungi, protozoa, mushroom-like organisms, slime molds, and algae belong to this kingdom.

There is a theory that the ancient cyanobacterium about 2.5 billion years ago was captured by the eukaryotic precursor cell, 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, have their own genetic apparatus.

From bacteria (prokaryotes) and archaea, the main difference between eukaryotes is the location of the genetic apparatus surrounded by a double membrane, protected by a strong shell of the nucleus. There are multinucleated organisms. They have linear DNA linked to histones, the proteins in which the strands are packed. In bacteria, the DNA is circular, not linked by histones.

The cell has dozens of permanent structures - its organelles that provide vital activity, each of which is separated by a membrane by one or more. 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, iron.

The size of eukaryotes is thousands of times larger than prokaryotes. This is why they need to consume large amounts of protein for food to keep them 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,
• melanosoma,
• cilia, flagella,
• cell wall.

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

The ribosome, being an organoid, has the shape of a sphere, carries out translation (protein synthesis from amino acids). Ribosomes are large and small.

Eukaryotic cell structure

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

Rough (granular) endoplasmic reticulum consists of branches, characterized by the presence of bubbles, tubes and cavities. It is surrounded by a membrane envelope. Its surface contains ribosomes that synthesize proteins.

The Golgi apparatus is a structure consisting of membranes and "cisterns" that helps to remove substances from the granular endoplasmic reticulum. In appearance it resembles tubes collected in piles. In the cisterns, proteins mature; each section contains its own set of enzymes. The vesicles, separating from the reticulum, continuously attach to the Golgi apparatus. When the protein is ready to move, the vesicles are detached and delivered to the desired organelle. The Golgi apparatus sorts substances, directing some of them to the plasma membrane, others to lysosomes.

Smooth (agranular) endoplasmic reticulum does not have ribosomes. Responsible for metabolic processes. Carries out the synthesis of lipids, fatty acids, steroids. The tissues of the liver and adrenal glands are composed of a smooth endoplasmic reticulum.

Mitochondria are organelles that oxidize organic compounds, using energy to support the life of the entire body. They can vary in shape, the amount contained in one cell can vary from one mitochondria to hundreds of thousands. It contains a circular spiral DNA molecule.

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

Hyaloplasm is an intracellular fluid.

Lysosome is an organoid, a type of vesicle surrounded by a membrane that contains enzymes. Performs the function of digesting molecules through secretion. Prokaryotes do not have lysosomes.

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

Melanosomes are present in animals and contain light-absorbing pigments, in particular melanin.

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

Flagella can also be found in prokaryotes. In bacteria, they are much thinner, in short, they cannot bend. Eukaryotic flagella are longer than cilia, although they are similar in structure. In archaea, flagella are somewhat thinner, differing in structure.

Cell wall, first of all, provides protection of all internal structures from external factors, and also carries out the transportation of substances. Consists of murein, the structure of which affects the degree of staining by the Gram method. Some bacteria, algae, fungi, archaea also have a cell wall. Also, bacteria can form a capsule - a slimy 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 a while, the cells become haloploid again, dividing. This method is completely uncommon for 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, by fermentation, food is "digested" to a consistency that can penetrate the cell membrane.

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

Also, eukaryotes are able to absorb liquid. Pinocytosis is the ability of all eukaryotic cells to absorb molecules of water and other liquid substances, satisfying their need for drinking.

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

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Organelles- constant, necessarily present, components of the cell that perform specific functions.

Endoplasmic reticulum

Endoplasmic reticulum (EPS), or endoplasmic reticulum (ER), Is a one-membrane organoid. It is a system of membranes that form "cisterns" and channels, connected to each other and limiting a single internal space - the EPS cavity. The membranes, on the one hand, are connected with the cytoplasmic membrane, on the other, with the outer nuclear membrane. There are two types of EPS: 1) rough (granular), containing ribosomes on its surface, and 2) smooth (agranular), whose membranes do not carry ribosomes.

Functions: 1) transport of substances from one part of the cell to another, 2) division of the cell cytoplasm into compartments ("compartments"), 3) synthesis of carbohydrates and lipids (smooth EPS), 4) protein synthesis (rough EPS), 5) the place of formation of the Golgi apparatus ...

Or Golgi complex, Is a one-membrane organoid. It is a stack of flattened "tanks" with widened edges. A system of small one-membrane bubbles (Golgi bubbles) is associated with them. Each stack usually consists of 4-6 "cisterns", is a structural and functional unit of the Golgi apparatus and is called a dictyosome. The number of dictyosomes in a cell ranges from one to several hundred. In plant cells, dictyosomes are isolated.

The Golgi apparatus is usually located near the cell nucleus (in animal cells, it is often near the cell center).

Functions of the Golgi apparatus: 1) accumulation of proteins, lipids, carbohydrates, 2) modification of incoming organic substances, 3) "packing" proteins, lipids, carbohydrates into membrane vesicles, 4) secretion of proteins, lipids, carbohydrates, 5) synthesis of carbohydrates and lipids, 6) place of formation lysosomes. The secretory function is the most important, therefore the Golgi apparatus is well developed in secretory cells.

Lysosomes

Lysosomes- one-membrane organelles. They are small bubbles (diameter from 0.2 to 0.8 microns) containing a set of hydrolytic enzymes. Enzymes are synthesized on a rough EPS, transferred to the Golgi apparatus, where they are modified and packaged into membrane vesicles, which, after separation from the Golgi apparatus, become lysosomes proper. The lysosome can contain from 20 to 60 different types of hydrolytic enzymes. The breakdown of substances using enzymes is called lysis.

Distinguish: 1) primary lysosomes, 2) secondary lysosomes... Primary lysosomes are called that are detached from the Golgi apparatus. Primary lysosomes are a factor providing exocytosis of enzymes from the cell.

Secondary lysosomes are called, formed as a result of the fusion of primary lysosomes with endocytic vacuoles. In this case, they digest the substances that entered the cell by phagocytosis or pinocytosis, so they can be called digestive vacuoles.

Autophagy- the process of destruction of structures unnecessary to the cell. First, the structure to be destroyed is surrounded by a single membrane, then the formed membrane capsule merges with the primary lysosome, as a result of which a secondary lysosome (autophagic vacuole) is also formed, in which this structure is digested. The products of digestion are assimilated by the cytoplasm of the cell, but part of the material remains undigested. The secondary lysosome containing this undigested material is called the residual body. Undigested particles are removed from the cell by exocytosis.

Autolysis- self-destruction of the cell, resulting from the release of the contents of the lysosomes. Normally, autolysis takes place during metamorphoses (disappearance of the tail in a frog tadpole), involution of the uterus after childbirth, in foci of tissue necrosis.

Functions of lysosomes: 1) intracellular digestion of organic substances, 2) destruction of unnecessary cellular and non-cellular structures, 3) participation in the processes of cell reorganization.

Vacuoles

Vacuoles- one-membrane organelles are "containers" filled with aqueous solutions of organic and inorganic substances. The EPS and the Golgi apparatus are involved in the formation of vacuoles. Young plant cells contain many small vacuoles, which then, as the cells grow and differentiate, merge with each other and form one large central vacuole... The central vacuole can occupy up to 95% of the volume of a mature cell, while the nucleus and organelles are pushed back to the cell membrane. The membrane that limits the plant vacuole is called tonoplast. The liquid that fills the plant vacuole is called cell sap... The composition of cell sap includes water-soluble organic and inorganic salts, monosaccharides, disaccharides, amino acids, end or toxic metabolic products (glycosides, alkaloids), some pigments (anthocyanins).

In animal cells, there are small digestive and autophagic vacuoles belonging to the group of secondary lysosomes and containing hydrolytic enzymes. In unicellular animals, there are also contractile vacuoles that perform the function of osmoregulation and excretion.

Vacuole functions: 1) accumulation and storage of water, 2) regulation of water-salt metabolism, 3) maintenance of turgor pressure, 4) accumulation of water-soluble metabolites, reserve nutrients, 5) coloring of flowers and fruits and thus attracting pollinators and seed distributors, 6) see. functions of lysosomes.

Endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles form single vacuolar network of the cell, the individual elements of which can pass into each other.

Mitochondria

1 - outer membrane;
2 - inner membrane; 3 - matrix; 4 - crista; 5 - multienzyme system; 6 - circular DNA.

The shape, size and number of mitochondria are extremely variable. In shape, mitochondria can be rod-shaped, rounded, spiral, cupped, branched. The length of mitochondria ranges from 1.5 to 10 microns, the diameter is from 0.25 to 1.00 microns. The number of mitochondria in a cell can reach several thousand and depends on the metabolic activity of the cell.

The mitochondrion is bounded by two membranes. The outer membrane of mitochondria (1) is smooth, the inner membrane (2) forms numerous folds - crista(4). Crystals increase the surface area of ​​the inner membrane, on which multienzyme systems (5) are located, participating in the synthesis of ATP molecules. The inner space of mitochondria is filled with a matrix (3). The matrix contains circular DNA (6), specific mRNA, ribosomes of the prokaryotic type (70S-type), enzymes of the Krebs cycle.

Mitochondrial DNA is not bound to proteins (“naked”), is attached to the inner mitochondrial membrane and carries information about the structure of about 30 proteins. Much more proteins are required to build mitochondria, so information about most mitochondrial proteins is contained in nuclear DNA, and these proteins are synthesized in the cytoplasm of the cell. Mitochondria are able to reproduce autonomously by dividing in two. Between the outer and inner membranes there is proton reservoir where H + accumulates.

Mitochondrial functions: 1) synthesis of ATP, 2) oxygen decomposition of organic substances.

According to one of the hypotheses (the theory of symbiogenesis), mitochondria evolved from ancient free-living aerobic prokaryotic organisms, which, having accidentally entered the host cell, then formed a mutually beneficial symbiotic complex with it. This hypothesis is supported by the following data. First, mitochondrial DNA has the same structural features as the DNA of modern bacteria (closed in a ring, not associated with proteins). Secondly, the mitochondrial ribosomes and ribosomes of bacteria belong to the same type - the 70S-type. Third, the mitochondrial division mechanism is similar to that of bacteria. Fourth, the synthesis of mitochondrial and bacterial proteins is inhibited by the same antibiotics.

Plastids

1 - outer membrane; 2 - inner membrane; 3 - stroma; 4 - thylakoid; 5 - grain; 6 - lamellae; 7 - starch grains; 8 - lipid drops.

Plastids are characteristic only of plant cells. Distinguish three main types of plastids: leukoplasts - colorless plastids in the cells of unpainted parts of plants, chromoplasts - colored plastids, usually yellow, red and orange, chloroplasts - green plastids.

Chloroplasts. In the cells of higher plants, chloroplasts have the form of a biconvex lens. The length of chloroplasts ranges from 5 to 10 microns, the diameter is from 2 to 4 microns. Chloroplasts are limited by two membranes. The outer membrane (1) is smooth, the inner membrane (2) has a complex folded structure. The smallest fold is called thylakoid(4). A group of thylakoids stacked like a stack of coins is called grain(5). The chloroplast contains an average of 40-60 grains, staggered. The grains are connected to each other by flattened channels - lamellae(6). Photosynthetic pigments and enzymes are built into the thylakoid membranes, which ensure the synthesis of ATP. The main photosynthetic pigment is chlorophyll, which determines the green color of chloroplasts.

The inner space of chloroplasts is filled stroma(3). The stroma contains circular “naked” DNA, 70S-type ribosomes, Calvin cycle enzymes, and starch grains (7). There is a proton reservoir inside each thylakoid, and H + accumulates. Chloroplasts, like mitochondria, are capable of autonomous reproduction by dividing in two. They are found in the cells of the green parts of higher plants, especially the chloroplasts in the leaves and green fruits. Chloroplasts of lower plants are called chromatophores.

Chloroplast function: photosynthesis. Chloroplasts are believed to have evolved from ancient endosymbiotic cyanobacteria (symbiogenesis theory). The basis for this assumption is the similarity of chloroplasts and modern bacteria in a number of features (circular, “naked” DNA, 70S-type ribosomes, reproduction method).

Leukoplasts. The shape varies (spherical, rounded, cupped, etc.). Leukoplasts are limited by two membranes. The outer membrane is smooth, the inner membrane forms few thylakoids. The stroma contains circular “naked” DNA, 70S-type ribosomes, enzymes for the synthesis and hydrolysis of reserve nutrients. There are no pigments. Cells of underground plant organs (roots, tubers, rhizomes, etc.) have especially many leukoplasts. Leukoplast function: synthesis, accumulation and storage of reserve nutrients. Amyloplasts- leukoplasts, which synthesize and accumulate starch, elioplasts- oils, proteinoplasts- proteins. Different substances can accumulate in the same leukoplast.

Chromoplasts. Limited by two membranes. The outer membrane is smooth, the inner or also smooth, or forms single thylakoids. The stroma contains circular DNA and pigments - carotenoids, which give chromoplasts a yellow, red or orange color. The form of accumulation of pigments is different: in the form of crystals, dissolved in lipid drops (8), etc. Contained in the cells of mature fruits, petals, autumn leaves, rarely root crops. Chromoplasts are considered the final stage of plastid development.

Chromoplast function: coloring flowers and fruits and thus attracting pollinators and seed distributors.

All types of plastids can be formed from proplastids. Proplastids- small organelles contained in meristematic tissues. Since plastids have a common origin, interconversions are possible between them. Leukoplasts can turn into chloroplasts (greening of potato tubers in the light), chloroplasts - into chromoplasts (yellowing of leaves and reddening of fruits). The transformation of chromoplasts into leukoplasts or chloroplasts is considered impossible.

Ribosomes

1 - large subunit; 2 - small subunit.

Ribosomes- non-membrane organelles, about 20 nm in diameter. Ribosomes consist of two subunits - large and small, into which they can dissociate. The chemical composition of ribosomes is proteins and rRNA. RRNA molecules make up 50-63% of the mass of the ribosome and form its structural framework. There are two types of ribosomes: 1) eukaryotic (with the sedimentation constants of the whole ribosome - 80S, small subunit - 40S, large - 60S) and 2) prokaryotic (respectively 70S, 30S, 50S).

The eukaryotic type ribosomes include 4 rRNA molecules and about 100 protein molecules, the prokaryotic type - 3 rRNA molecules and about 55 protein molecules. During protein biosynthesis, ribosomes can "work" singly or combine into complexes - polyribosomes (polysomes)... In such complexes, they are linked to each other by one mRNA molecule. Prokaryotic cells have only 70S-type ribosomes. Eukaryotic cells have ribosomes of both 80S-type (rough membranes of EPS, cytoplasm) and 70S-type (mitochondria, chloroplasts).

The subunits of the eukaryotic ribosome are formed in the nucleolus. The union of subunits into a whole ribosome occurs in the cytoplasm, usually during protein biosynthesis.

Ribosome function: assembly of the polypeptide chain (protein synthesis).

Cytoskeleton

Cytoskeleton formed by microtubules and microfilaments. Microtubules are cylindrical unbranched structures. The length of the microtubules ranges from 100 μm to 1 mm, the diameter is about 24 nm, and the wall thickness is 5 nm. The main chemical component is tubulin protein. Microtubules are destroyed by colchicine. Microfilaments - filaments with a diameter of 5-7 nm, consist of actin protein. Microtubules and microfilaments form complex weaves in the cytoplasm. Cytoskeleton functions: 1) determination of the cell shape, 2) support for organelles, 3) formation of the division spindle, 4) participation in cell movements, 5) organization of the cytoplasmic flow.

Includes two centrioles and a centrosphere. Centriole is a cylinder, the wall of which is formed by nine groups of three merged microtubules (9 triplets), interconnected at certain intervals by cross-linking. The centrioles are paired where they are at right angles to each other. Before cell division, centrioles diverge to opposite poles, and a daughter centriole appears near each of them. They form a spindle of division, which contributes to an even distribution of genetic material between daughter cells. In the cells of higher plants (gymnosperms, angiosperms), the cell center does not have centrioles. Centrioles belong to self-reproducing organelles of the cytoplasm, they arise as a result of duplication of existing centrioles. Functions: 1) ensuring the divergence of chromosomes to the poles of the cell during mitosis or meiosis, 2) the center of organization of the cytoskeleton.

Organelles of movement

Not present in all cells. Organoids of movement include cilia (ciliates, epithelium of the respiratory tract), flagella (flagellates, sperm), pseudopods (rhizopods, leukocytes), myofibrils (muscle cells), etc.

Flagella and cilia- filamentous organelles, represent an axoneme bounded by a membrane. Axoneme - cylindrical structure; the wall of the cylinder is formed by nine pairs of microtubules; in its center there are two single microtubules. At the base of the axoneme are the basal bodies, represented by two mutually perpendicular centrioles (each basal body consists of nine triplets of microtubules, there are no microtubules in its center). The length of the flagellum reaches 150 microns, the cilia are several times shorter.

Myofibrils consist of actin and myosin myofilaments, which ensure the contraction of muscle cells.

Go to lectures number 6"Eukaryotic cell: cytoplasm, cell membrane, structure and function of cell membranes"

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

Features of the structure of cells

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

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

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


11. The core;
12. Nucleolus;
13. Peroxisome.

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

Features of the structure of cells of eukaryotes and prokaryotes

A whole article can be written about the structural features of the cells of eukaryotes and prokaryotes, but still we will try to highlight only the important parts and analyze the difference between one kingdom over another. Let's start describing the difference moving to the core.

Cell Comparison Chart
Comparison	Prokaryotic cell (prenuclear)	Eukaryotic cell (nuclear)
Cage size	0.5-10 μm	10-100 μm
DNA molecule	One circular molecule in the cytoplasm	Several linear molecules of DNA found in the nucleus
Cell division	Simple binary	Meiosis or mitosis
Cell wall	Is composed of polymeric protein-carbohydrate molecules	Plant cells have cellulose. Animals do not have cells.
Cell membrane	There is	There is
Cytoplasm	There is	There is
EPR *	No	There is
Golgi apparatus	No	There is
Mitochondria	No	There is
Vacuoles	No	Most cells have
Cytoskeleton	No	There is
Centriole	No	Have animal cells
Ribosomes	There is	There is
Lysosomes	No	There is
Core	Nuclear region with no nuclear membrane	Is surrounded by a membrane

* EPR - Endoplasmic reticulum

A cell is an elementary unit of the structure and vital activity of all alive organisms(except viruses, which are often spoken of as non-cellular forms of life), which has its own metabolism, is capable of independent existence, self-reproduction and development. All living organisms either, as multicellular animals, plants and mushrooms, consist of many cells, or, as many protozoa and bacteria are unicellular organisms... The section of biology dealing with the study of the structure and vital activity of cells was named cytology... Recently, it is also customary to talk about cell biology, or cell biology.

Distinctive features of plant and animal cells

Signs	Plant cell	Animal cage
Plastids	Chloroplasts, chromoplasts, leukoplasts	Absent
Food method	Autotrophic (phototrophic, chemotrophic)
ATP synthesis	In chloroplasts, mitochondria	In mitochondria
Cleavage of ATP	In chloroplasts and all parts of the cell where energy is needed	In all parts of the cell where energy is needed
Cell center	In lower plants	In all cells
Cellulose cell wall	Located outside of the cell membrane	Absent
Inclusions	Reserve nutrients in the form of starch grains, protein, oil drops; vacuoles with cell sap; salt crystals	Reserve nutrients in the form of grains and drops (proteins, fats, carbohydrates, glycogen); end products of metabolism, salt crystals, pigments
	Large cavities filled with cell sap - an aqueous solution of various substances (spare or final products). Osmotic reservoirs of the cell.	Contractile, digestive, excretory vacuoles. Usually small.

General signs 1. The unity of structural systems - cytoplasm and nucleus. 2. The similarity of the processes of metabolism and energy. 3. Unity of the principle of the hereditary code. 4. Universal membrane structure. 5. The unity of the chemical composition. 6. The similarity of the process of cell division.

Cell structure

All cellular life forms on Earth can be divided into two kingdoms based on the structure of their constituent cells:

prokaryotes (prenuclear) are simpler in structure and arose earlier in the process of evolution;

eukaryotes (nuclear) - more complex, arose later. The cells that make up the human body are eukaryotic.

Despite the variety of forms, the organization of cells of all living organisms is subordinated to uniform structural principles.

The contents of the cell are separated from the environment by the plasma membrane, or plasma membrane. Inside the cell is filled with cytoplasm, in which various organoids and cellular inclusions are located, as well as genetic material in the form of a DNA molecule. Each of the organoids of the cell performs its own special function, and in the aggregate, they all determine the vital activity of the cell as a whole.

Prokaryotic cell

The structure of a typical prokaryotic cell: capsule, cell wall, plasmolemma, cytoplasm,ribosomes, plasmid, drank, flagellum,nucleoid.

Prokaryotes (from lat. pro- before, before and Greek κάρῠον - core, nut) - organisms that, unlike eukaryotes, do not have a formed cell nucleus and other internal membrane organelles (with the exception of flat cisterns in photosynthetic species, for example, in cyanobacteria). The only large circular (in some species - linear) double-stranded molecule DNA, which contains the bulk of the genetic material of the cell (the so-called nucleoid) does not form a complex with proteins histones(so called chromatin). Prokaryotes include bacteria, including cyanobacteria(blue-green algae), and archaea... The descendants of prokaryotic cells are organelles eukaryotic cells - mitochondria and plastids... The main content of the cell, which fills its entire volume, is a viscous granular cytoplasm.

Eukaryotic cell

Eukaryotes are organisms that, in contrast to prokaryotes, have a formalized cellular core separated from the cytoplasm by the nuclear envelope. The genetic material is enclosed in several linear double-stranded DNA molecules (depending on the type of organisms, their number per nucleus can vary from two to several hundred), attached from the inside to the membrane of the cell nucleus and forming in the vast majority (except dinoflagellates) a complex with proteins histones called chromatin... In eukaryotic cells there is a system of internal membranes, which, in addition to the nucleus, form a number of other organoids (endoplasmic reticulum, Golgi apparatus and etc.). In addition, the vast majority have permanent intracellular symbionts- prokaryotes - mitochondria, and in algae and plants - also plastids.

Eukaryotic cell structure

A schematic representation of an animal cell. (When you click on any of the names of the component parts of the cell, you will go to the corresponding article.)

Surface complex of an animal cell

Consists of glycocalyx, plasmalemma and the cortical layer located under it cytoplasm... The plasma membrane is also called the plasmalemma, the outer cell membrane. It is a biological membrane, about 10 nanometers thick. First of all, it provides a delimiting function in relation to the environment external to the cell. In addition, she performs transport function... The cell does not spend energy to maintain the integrity of its membrane: the molecules are retained according to the same principle by which fat molecules are held together - hydrophobic it is thermodynamically more favorable for parts of molecules to be located in close proximity to each other. Glycocalyx is a molecule of oligosaccharides, polysaccharides, glycoproteins and glycolipids "anchored" in the plasma membrane. Glycocalyx performs receptor and marker functions. Plasma membrane animals cells mainly consists of phospholipids and lipoproteins with embedded molecules of proteins, in particular, surface antigens and receptors. In the cortical (adjacent to the plasma membrane) layer of the cytoplasm there are specific elements of the cytoskeleton - actin microfilaments ordered in a certain way. The main and most important function of the cortical layer (cortex) is pseudopodial reactions: ejection, attachment and contraction of pseudopodia. In this case, the microfilaments are rearranged, lengthened or shortened. The shape of the cell also depends on the structure of the cytoskeleton of the cortical layer (for example, the presence of microvilli).

The unity of the structure of cells.

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

The internal environment of a living cell, limited by the plasma membrane, is called cytoplasm. It includes hyaloplasm(basic transparent substance) and cell organelles, as well as various non-permanent structures - inclusion. Organelles that are in any cell also include ribosomes, on which there is protein synthesis.

The structure of eukaryotic cells.

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

Ribosomes- non-membrane organelles.

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

For the synthesis of proteins, carbohydrates and fats, energy is needed, which is produced in the eukaryotic cell by the "energy stations" of the cell - mitochondria.

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

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

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

A cell can contain organelles that do not have a membrane structure, for example, ribosomes and cytoskeleton.

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

There are organelles that are characteristic only of plant cells - plastids. There are: chloroplasts, chromoplasts and leukoplasts. The process of photosynthesis takes place in chloroplasts.

In plant cells also vacuoles- Cell waste products, which are reservoirs of water and compounds dissolved in it. The eukaryotic organisms include plants, animals, and fungi.

The structure of prokaryotic cells.

Prokaryotes- unicellular organisms, in the cells of which there is no nucleus.

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

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

Protein synthesis in prokaryotes occurs on ribosomes. There are few organelles in prokaryotic cells.

Hypotheses of the origin of eukaryotic cell organelles.

Prokaryotic cells appeared on Earth earlier than eukaryotic ones.

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

2) Invagination hypothesis- claims that the origin of the eukaryotic cell comes from the fact that the ancestral form was an aerobic prokaryote. Organelles in it arose as a result of invagination and detachment of parts of the membrane with subsequent functional specialization in the nucleus, mitochondria, chloroplasts of other organelles.