Schematic representation of the cell nucleus, endoplasmic reticulum and Golgi complex.
(1) Cell nucleus.
(2) The pores of the nuclear membrane.
(3) Granular endoplasmic reticulum.
(4) Agranular endoplasmic reticulum.
(5) Ribosomes on the surface of the granular endoplasmic reticulum.
(6) Macromolecules
(7) Transport vesicles.
(8) Golgi complex.
(9) Tsis-Golgi
(10) Trans-Golgi
(11) Golgi Cisterns

Discovery history

For the first time, the endoplasmic reticulum was discovered by the American scientist K. Porter in 1945 by means of electron microscopy.

Structure

The endoplasmic reticulum consists of an extensive network of tubules and pockets surrounded by a membrane. The area of ​​the membranes of the endoplasmic reticulum is more than half of the total area of ​​all cell membranes.

The EPR membrane is morphologically identical to the membrane of the cell nucleus and forms one whole with it. Thus, the cavities of the endoplasmic reticulum open into the intermembrane cavity of the nuclear envelope. EPS membranes provide active transport of a number of elements against the concentration gradient. The filaments that form the endoplasmic reticulum have a diameter of 0.05-0.1 microns (sometimes up to 0.3 microns), the thickness of the bilayer membranes forming the wall of the tubules is about 50 angstroms (5 nm, 0.005 microns). These structures contain unsaturated phospholipids, as well as some cholesterol and sphingolipids. They also contain proteins.

The tubes, the diameter of which ranges from 0.1 to 0.3 microns, are filled with homogeneous contents. Their function is to carry out communication between the contents of the EPS bubbles, external environment and the cell nucleus.

The endoplasmic reticulum is not a stable structure and is subject to frequent changes.

There are two types of EPR:

• granular (rough) endoplasmic reticulum;
• agranular (smooth) endoplasmic reticulum.

On the surface of the granular endoplasmic reticulum there is a large number of ribosomes that are absent on the surface of the agranular ER.

Granular and agranular endoplasmic reticulum perform different functions in the cell.

Functions of the endoplasmic reticulum

With the participation of the endoplasmic reticulum, translation and transport of proteins, synthesis and transport of lipids and steroids occurs. EPR is also characterized by the accumulation of synthesis products. The endoplasmic reticulum also takes part in the creation of a new nuclear envelope (for example, after mitosis). The endoplasmic reticulum contains an intracellular calcium store, which is, in particular, a mediator of muscle cell contraction. A special form of the endoplasmic reticulum is located in the cells of muscle fibers - sarcoplasmic reticulum.

Functions of the agranular endoplasmic reticulum

The agranular endoplasmic reticulum is involved in many metabolic processes. Also, the agranular endoplasmic reticulum plays important role in carbohydrate metabolism, neutralization of poisons and storage of calcium. Agranular endoplasmic reticulum enzymes are involved in the synthesis of various lipids and phospholipids, fatty acids and steroids. In particular, in this regard, agranular endoplasmic reticulum predominates in the cells of the adrenal glands and liver.

Hormone synthesis

The hormones that are formed in the agranular EPS include, for example, the sex hormones of vertebrates and the steroid hormones of the adrenal glands. The cells of the testes and ovaries, which are responsible for the synthesis of hormones, contain a large amount of agranular endoplasmic reticulum.

Accumulation and conversion of carbohydrates

Carbohydrates in the body are stored in the liver as glycogen. Through glycogenolysis, glycogen in the liver is transformed into glucose, which is the most important process in maintaining blood glucose levels. One of the enzymes of agranular EPR cleaves a phospho group from the first product of glycogenolysis, glucose-6-phosphate, thus allowing glucose to leave the cell and increase blood sugar levels.

Neutralization of poisons

The smooth endoplasmic reticulum of liver cells takes an active part in neutralizing all kinds of poisons. Enzymes of smooth EPR attach hydrophilic radicals to the molecules of toxic substances, as a result of which the solubility of toxic substances in the blood and urine increases, and they are quickly eliminated from the body. In the case of a continuous intake of poisons, medicines or alcohol, large quantity agranular EPR, which increases the dose of the active substance required to achieve the previous effect.

Role of EPS as a calcium depot

The concentration of calcium ions in EPS can reach 10–3 mol, while in the cytosol it is about 10–7 mol (at rest). Under the influence of inositol triphosphate and some other stimuli, calcium is released from EPS through facilitated diffusion. The return of calcium to EPS is provided by active transport. At the same time, the EPS membrane provides active transport of calcium ions against concentration gradients of large orders. Both the intake and release of calcium ions in the EPS is in a delicate relationship with physiological conditions.

The concentration of calcium ions in the cytosol affects many intracellular and intercellular processes, such as activation or inactivation of enzymes, gene expression, synaptic plasticity of neurons, contractions of muscle cells, release of antibodies from cells immune system.

Sarcoplasmic reticulum

A special form of agranular endoplasmic reticulum, sarcoplasmic reticulum, is EPS in muscle cells, in which calcium ions are actively pumped from

Endoplasmic reticulum (EPS), or endoplasmic reticulum (ER), was discovered only with the advent of the electron microscope. EPS is present only in eukaryotic cells and is a complex system of membranes that form flattened cavities and tubules. Together, it looks like a web. EPS refers to one-membrane cell organelles.

The EPS membranes extend from the outer membrane of the nucleus and are structurally similar to it.

Endoplasmic reticulum divided into smooth (agranular) and rough (granular). The latter is dotted with ribosomes attached to it (because of this, "roughness" occurs). The main function of both types is associated with the synthesis and transport of substances. Only the rough one is responsible for protein, and the smooth one is responsible for carbohydrates and fats.

By its structure, EPS is a set of paired parallel membranes that permeate almost the entire cytoplasm. A pair of membranes forms a plate (the cavity inside has different width and height), but the smooth endoplasmic reticulum in to a greater extent has a tubular structure. Such flattened membrane sacs are called EPS tanks.

Ribosomes located on the rough EPS synthesize proteins that enter the EPS channels, mature (acquire a tertiary structure) there and are transported. These proteins first synthesize a signal sequence (consisting mainly of non-polar amino acids), the configuration of which corresponds to a specific EPS receptor. As a result, the ribosome and the endoplasmic reticulum are linked. In this case, the receptor forms a channel for the transition of the synthesized protein into the EPS cisterns.

After the protein is in the channel of the endoplasmic reticulum, the signal sequence is separated from it. After that, it folds into its tertiary structure. When transported along EPS, the protein acquires a number of other changes (phosphorylation, the formation of a bond with a carbohydrate, i.e., conversion into a glycoprotein).

Most of the proteins trapped in the rough EPS, then enter the Golgi apparatus (complex). From there, proteins are either secreted from the cell, or enter other organelles (usually lysosomes), or are deposited as granules of storage substances.

It should be borne in mind that not all cell proteins are synthesized on the rough EPS. Part (usually a smaller one) is synthesized by free ribosomes in the hyaloplasm, such proteins are used by the cell itself. Their signal sequence is not synthesized because it is unnecessary.

The main function of the smooth endoplasmic reticulum is lipid synthesis(fat). For example, EPS of intestinal epithelium synthesizes them from fatty acids and glycerol absorbed from the intestine. Then lipids enter the Golgi complex. In addition to intestinal cells, smooth EPS is well developed in cells that secrete steroid hormones (steroids are lipids). For example, in the cells of the adrenal glands, interstitial cells of the testes.

The synthesis and transport of proteins, fats and carbohydrates are not the only functions of EPS. In baking, the endoplasmic reticulum is involved in detoxification processes. A special form of smooth EPS - sarcoplasmic reticulum - is present in muscle cells and provides contraction due to the pumping of calcium ions.

The structure, volume and functionality of the endoplasmic reticulum of a cell is not constant throughout the cell cycle, but is subject to one or another change.

The endoplasmic reticulum is one of the most important organelles in the eukaryotic cell. Its second name is the endoplasmic reticulum. EPS is of two types: smooth (agranular) and rough (granular). The more active the metabolism in the cell, the greater the amount of EPS there.

Structure

It is a vast labyrinth of canals, cavities, vesicles, "cisterns" that are closely connected and communicate with each other. This organoid is covered with a membrane that communicates with both the cytoplasm and the outer cell membrane. The volume of the cavities is different, but they all contain a homogeneous liquid, which allows interaction between the cell nucleus and the external environment. Sometimes there are branches from the main network in the form of single bubbles. Rough EPS differs from smooth by the presence of outer surface membranes a large number ribosomes.

Functions

• Functions of agranular EPS. It takes part in the formation of steroid hormones (for example, in the cells of the adrenal cortex). EPS, contained in liver cells, is involved in the destruction of certain hormones, drugs and harmful substances, and in the processes of converting glucose, which is formed from glycogen. Also, the agranular network produces phospholipids, which are necessary for the construction of membranes of all types of cells. And in the reticulum of muscle tissue cells, calcium ions are deposited, which are necessary for muscle contraction. This type of smooth endoplasmic reticulum is also called the sarcoplasmic reticulum.
• Functions of granular EPS. First of all, the production of proteins occurs in the granular reticulum, which will subsequently be removed from the cell (for example, the synthesis of secretion products of glandular cells). And also in a rough EPS, synthesis and assembly of phospholipids and multi-chain proteins takes place, which are then transported to the Golgi apparatus.
• Common functions for both smooth endoplasmic reticulum and rough endoplasmic reticulum are the demarcation function. Due to these organelles, the cell is divided into compartments (compartments). And in addition, these organelles are transporters of substances from one part of the cell to another.

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) the division of the cytoplasm of the cell into compartments ("compartments"), 3) the 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 located near the cell center).

Functions of the Golgi apparatus: 1) the accumulation of proteins, lipids, carbohydrates, 2) modification of the received organic matter, 3) "packing" in membrane vesicles of proteins, lipids, carbohydrates, 4) secretion of proteins, lipids, carbohydrates, 5) synthesis of carbohydrates and lipids, 6) the place of formation of 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 packed into membrane vesicles, which, after being separated from the Golgi apparatus, become lysosomes proper. The lysosome can contain 20 to 60 different types 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 resulting 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 aqueous solutions 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 cell sap contains 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, spare nutrients, 5) coloring of flowers and fruits and thus attracting pollinators and seed distributors, 6) see the functions of lysosomes.

Endoplasmic reticulum, Golgi apparatus, lysosomes and vacuoles form single vacuolar network of the cell, individual elements which can transform 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 (2) forms numerous folds - crista(4). Crystals increase the surface area of ​​the inner membrane, on which the multienzyme systems (5) are located, participating in the synthesis processes ATP molecules. Inner space mitochondria are filled with 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 originated 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 suppressed 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 uncolored parts of plants, chromoplasts - colored plastids usually yellow, red and orange flowers, chloroplasts are green plastids.

Chloroplasts. In cages higher plants chloroplasts are in 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 (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 causes green color 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 contained 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 transform 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. Chemical composition ribosomes - 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 sedimentation constants of the whole ribosome - 80S, small subunit - 40S, large - 60S) and 2) prokaryotic (respectively 70S, 30S, 50S).

The eukaryotic ribosome contains 4 rRNA molecules and about 100 protein molecules, the prokaryotic type contains 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 shape of the cell, 2) support for organelles, 3) formation of the spindle of division, 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.

Movement organelles

Not present in all cells. The organelles of movement include cilia (ciliates, epithelium respiratory tract), flagella (flagellates, spermatozoa), pseudopods (roots, 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"

An important function of the PAK is the function individualization... It manifests itself in the difference between cells in the chemical structure of the components of the glycocalyx. These differences may relate to the structure of the supramembrane domains of several integral and semi-integral proteins. Great importance in the implementation of the individualization function, there are differences in the carbohydrate components of the glycocalyx (oligosaccharides of glycolipids and PAA glycoproteins). These differences may relate to the glycocalyx of the same cells in different organisms. The different composition of the glycocalyx is also characteristic for different cells of one multicellular organism. The molecules responsible for the individualization function are called antigens... The structure of antigens is controlled by specific genes. Each gene can define several variants of one antigen. The body has a large number of different antigen systems. As a result, it has a unique set of different antigen variants. This is the manifestation of the function of individualization of the PAK.

The PAK is characterized by a locomotor function. It is realized in the form of movement of individual sections of the PAK or the entire cell. This function is carried out on the basis of the submembrane musculoskeletal system. With the help of mutual sliding and polymerization - depolarization of microfibrils and microtubules, protrusions of plasmolemma areas are formed in certain regions of the PAA. On this basis, endocytosis occurs. The coordinated movement of many parts of the PAK leads to the movement of the entire cell. The cells of the immune system, macrophages, are highly mobile. They are capable of phagocytosis of foreign substances and even whole cells and move almost throughout the body. Violation of the locomotor function of macrophages causes an increased sensitivity of the body to pathogens of infectious diseases. This is due to the involvement of macrophages in immune responses.

In addition to the considered universal functions of PAA, this cell subsystem can also perform other specialized functions.

6. Structure and function of eps.

The endoplasmic reticulum, or endoplasmic reticulum, is a system of flat membrane cisterns and membrane tubules. Membrane tanks and tubes are interconnected and form a membrane structure with a common content. This makes it possible to isolate certain areas of the cytoplasm from the main nialoplasm and to realize some specific cellular functions in them. As a result, functional differentiation of various zones of the cytoplasm occurs. The structure of the EPS membranes corresponds to the liquid-mosaic model. Morphologically, there are 2 types of EPS: smooth (agranular) and rough (granular). Smooth EPS is represented by a system of membrane tubes. Rough EPS is a membrane tank system. On the outer side of the rough EPS membranes there are ribosomes... Both types of EPS are structurally dependent - membranes of one type of EPS can transform into membranes of another type.

Functions of the endoplasmic reticulum:

Granular EPS is involved in the synthesis of proteins; complex protein molecules are formed in the channels.

Smooth EPS is involved in the synthesis of lipids and carbohydrates.

Transport of organic substances into the cell (via EPS channels).

Divides the cell into sections - in which different chemical reactions and physiological processes can occur simultaneously.

Smooth EPS is multifunctional. In its membrane there are proteins-0 enzymes that catalyze the synthesis of membrane lipids. In smooth EPS, some non-membrane lipids (steroid hormones) are also synthesized. Ca 2+ transporters are included in the membrane of this type of EPS. They transport calcium along a concentration gradient (passive transport). With passive transport, ATP is synthesized. With their help, the concentration of Ca 2+ in the hyaloplasm is regulated in smooth EPS. This parameter is important for regulating the work of microtubules and microfibrils. In muscle cells, smooth EPS regulates muscle contraction. In EPS, detoxification of many substances harmful to the cell (drugs) occurs. Smooth EPS can form membrane vesicles, or microbodies. Such bubbles carry out specific oxidative reactions in isolation from EPS.

Main function rough EPS is protein synthesis. This is determined by the presence of ribosomes on the membranes. The membrane of rough EPS contains special proteins riboforins... Ribosomes interact with riboforins and are fixed on the membrane in a specific orientation. All proteins synthesized in EPS have a terminal signal fragment. Protein synthesis takes place on ribosomes of rough EPS.

In the cisterns of the rough EPS, post-translational protein modification occurs.

7. Golgi complex and lysosomes. Structure and function .

The Golgi complex is a universal membrane organoid of eukaryotic cells. The structural part of the Golgi complex is represented by the system membrane tanks forming a stack of tanks. This stack is called a dictyosome. Membrane tubes and membrane vesicles depart from them.

The structure of the membranes of the Golgi complex corresponds to the liquid-mosaic structure. Membranes of different poles are classified according to the number of glycolipids and glycoproteins. At the proximal pole, new dictyosome cisterns are formed. Small membrane vesicles detach from areas of smooth EPS and move to the zone of the proximal pole. Here they merge and form a larger cistern. As a result of this process, substances that are synthesized in EPS can be transported into the tanks of the Golgi complex. Vesicles detach from the lateral surfaces of the distal pole, which are involved in endocytosis.

The Golgi complex has 3 common cellular functions:

Cumulative

Secretory

Aggregation

Certain biochemical processes take place in the tanks of the Golgi complex. As a result, the components of the membrane of the Golgi complex cisterns and the molecules inside these cisterns are chemically modified. In the membranes of the proximal pole cisterns there are enzymes that synthesize carbohydrates (polysaccharides) and attach them to lipids and proteins, i.e. glycosylation occurs. The presence of this or another carbohydrate component in glycosylated proteins determines their fate. Depending on this, proteins enter different areas of the cell and are secreted. Glycosylation is one of the stages of secretion maturation. In addition, proteins in the cisterns of the Golgi complex can be phosphorylated and acetylated. Free polysaccharides can be synthesized in the Golgi complex. Some of them undergo sulfation with the formation of mucopolysaccharides (glycosaminoglycans). Another option for secretion maturation is protein condensation. This process consists in the removal of water molecules from the secretory granules, which leads to a thickening of the secretion.

Also, the universality of the Golgi complex in eukaryotic cells is its participation in the formation lysosomes.

Lysosomes are membrane organelles of the cell. Inside the lysosomes there is a lysosomal matrix of mucopolysaccharides and proteins, enzymes.

The membrane of lysosomes is a derivative of the EPS membrane, but it has its own characteristics. This concerns the structure of the bilipid layer. In the lysosomal membrane, it is not continuous (not continuous), but includes lipid micelles. These micelles make up up to 25% of the lysosomal membrane surface. This structure is called lamellar-micellar. A variety of proteins are localized in the lysosomal membrane. These include enzymes: hydrolases, phospholipases; and low molecular weight proteins. Hydrolases are lysosome-specific enzymes. They catalyze hydrolysis (cleavage) reactions of high molecular weight substances.

Functions of lysosomes:

Digestion of particles during phagocytosis and pinocytosis.

Protective against phagocytosis

Autophagy

Autolysis in ontogenesis.

The main function of lysosomes is to participate in heterophagotic cycles (heterophagy) and autophagotic cycles (autophagy). During heterophagy, substances foreign to the cell are cleaved. Autophagy is associated with the breakdown of the cell's own substances. The usual variant of heterophagy begins with endocytosis and the formation of an endocytic vesicle. In this case, the vesicle is called a heterophagosome. In another variant of heterophagy, the stage of endocytosis of foreign substances is absent. In this case, the primary lysosome is immediately involved in exocytosis. As a result, matrix hydrolases end up in the cell glycocalyx and are able to break down extracellular foreign substances.