The Golgi apparatus is an important organelle that is present in almost every one. Perhaps the only cells lacking this complex are the erythrocytes of vertebrates. The functions of this structure are very diverse. It is in the tanks of the apparatus that all the compounds produced by the cell accumulate, after which they are further sorted, modified, redistributed and transported.

Despite the fact that the Golgi apparatus was discovered back in 1897, some of its functions are being actively studied to this day. Let's consider in more detail the features of its structure and functioning.

Golgi apparatus: structure

This organelle is a collection of membrane cisterns, which are closely adjacent to each other, resembling a stack. The structural and functional unit here is considered to be the dictyosome.

The dictyosome is a separate, independent part of the Golgi apparatus, which consists of 3 - 8 cisterns closely adjacent to each other. The stack of these membrane cisterns is surrounded by a system of small vacuoles and vesicles - this is how the transport of substances is carried out, as well as the connection of dictyosomes between themselves and other cellular structures. As a rule, they have only one dictyosome, while in plant structures there can be many of them.

In a dictyosome, it is customary to separate two ends - the cis and trans sides. The cis side faces the nucleus and the granular endoplasmic reticulum. Synthesized proteins and other compounds are transported here in the form of membrane vesicles. At this end of the dictyosome, new cisterns are constantly being formed.

The trance side is facing towards It is usually slightly wider. This includes compounds that have already gone through all the stages of modification. Small vacuoles and vesicles constantly detach from the lower cistern, which transport substances to the desired cell organelles.

Golgi apparatus: functions

As already mentioned, the functions of the organelle are very diverse.

  • This is where the newly synthesized protein molecules are modified. In most cases, a carbohydrate, sulfate or phosphorus radical is attached to a protein molecule. Thus, the Golgi apparatus is responsible for the formation of enzymes and proteins of lysosomes by protein.
  • The Golgi apparatus is responsible for the transport of modified proteins to specific areas of the cell. From the trans side, small bubbles are constantly separated, which contain the ready-made proteins.
  • Here the formation and transport of all lysosomal enzymes takes place.
  • In the cavities of the cisterns, lipids accumulate, and later the formation of lipoproteins - a complex of protein and lipid molecules.
  • The Golgi apparatus of a plant cell is responsible for the synthesis of polysaccharides, which are then used to form a plant, as well as mucus, pectins, hemicellulose and waxes.
  • After the division of the plant cell, the Golgi complex takes part in the formation of the cell plate.
  • In the sperm, this organelle takes part in the formation of acrosome enzymes, with the help of which the ovum membranes are destroyed during fertilization.
  • In the cells of the protozoa, the Golgi complex is responsible for the formation of which regulate

Of course, this is not a complete list of all functions performed. Modern scientists are still conducting a wide variety of research using the latest technology. It is likely that the list of functions of the Golgi complex will grow significantly in the next few years. But today we can say with certainty that this organelle supports the normal vital activity of both the cell and the entire organism as a whole.

The Golgi complex was discovered in 1898. This membrane structure is designed to excrete compounds that are synthesized in the endoplasmic reticulum. Let's take a closer look at this system below.

Golgi complex: structure

The apparatus is a stack of disc-shaped membrane tanks. These bags are slightly widened towards the edges. The cisterns are associated with the Golgi bubble system. In animal cells, there is one large or several stacks, which are connected by tubes; in plant cells, dictyosomes (several separate stacks) are found. The Golgi complex includes three sections. They are surrounded by membrane vesicles:

  • cis-department closest to the nucleus;
  • medial;
  • trans department (farthest from the nucleus).

These systems differ in their enzymatic set. In the cis department, the first pouch is called the "salvage cistern". With its help, the receptors that come from the endoplasmic intermediate reticulum move back. The cis enzyme is called phosphoglycosidase. It adds phosphate to mannose (carbohydrate). There are two enzymes in the medial section. These are, in particular, mennadiasis and N-acetylglucosamine transferase. The latter adds glycosamines. Enzymes of the trans-department: peptidase (it carries out proteolysis) and transferase (with its help there is a transfer of chemical groups).

Golgi complex: functions

This structure ensures the separation of proteins into the following three streams:

  1. Lysosomal. Through it, glycated proteins penetrate into the cis section of the Golgi apparatus. Some of them are phospholized. As a result, mannose-6-phosphate is formed - marketlysosomal enzymes. In the future, these phospholated proteins will enter the lysosomes, and will not be modified.
  2. Constitutive exocytosis (secretion). This stream includes proteins and lipids that have become components of the surface cellular apparatus, including the glycocalyx. Also, compounds that are part of the extracellular matrix may be present here.
  3. Induced secretion. This stream is penetrated by proteins that function outside the cell, the surface apparatus, in the internal environment in the body. Induced secretion is characteristic of secretory cells.

The Golgi complex takes part in the formation of mucous secretions - mucopolysaccharides (glycosaminoglycans). The apparatus also forms the carbohydrate components of the glycocalyx. They are mainly represented by glycolipids. The system also provides sulfation of protein and carbohydrate elements. The Golgi complex is involved in the partial proteolysis of proteins. In some cases, due to this, the compound changes from inactive to active form (for example, proinsulin is transformed into insulin).

Transfer of compounds from the endoplasmic reticulum (EPS)

The complex is asymmetrical. The cells located closer to the nucleus contain the most immature proteins. Vesicles - membrane vesicles - are continuously attached to these sacs. They bud off from the endoplasmic granular reticulum. On its membranes, the process of protein synthesis by ribosomes takes place. The transport of compounds from the endoplasmic reticulum to the Golgi complex is carried out indiscriminately. In this case, incorrectly or incompletely folded proteins continue to remain in the EPS. The reverse movement of compounds into the endoplasmic reticulum requires a special signal sequence and becomes possible due to the binding of these substances to membrane receptors in the cis-compartment.

Protein modification

In the cisterns of the complex, compounds that are intended for secretion, transmembrane, lysosomal and other substances, mature. These proteins are sequentially moved along the cisterns to the organelles. In them, their modifications begin - phospholation and glycation. During the first process, the remainder of phosphoric acid is attached to the proteins. In O-glycosylation, complex sugars are docked by means of an oxygen atom. Different tanks contain different catalytic enzymes. Consequently, with the proteins maturing in them, successively different processes take place. Undoubtedly, such a stepwise phenomenon must be controlled. As a kind of "quality mark" are polysaccharide residues (mannose, mainly). They mark the maturing proteins. Further movement of compounds through the cisterns is not fully understood by science, despite the fact that resistant substances remain to a lesser or greater extent associated with one sac.

Transport of proteins from the apparatus

Vesicles bud from the trans-section of the complex. They contain fully mature protein compounds. The main function of the complex is considered to be the sorting of proteins passing through it. The apparatus carries out the formation of a "three-way protein flow" - maturation and transport:

  1. Plasma membrane compounds.
  2. Secrets.
  3. Lysosomal enzymes.

By means of vesicular transport, proteins that have passed through the Golgi complex are delivered to certain sites in accordance with the "tags". This process is also not fully understood by science. It was found that the transport of proteins from the complex requires the participation of special membrane receptors. They recognize the compound and provide selective docking of the vesicle and this or that organelle.

Formation of lysosomes

Many hydrolytic enzymes pass through the apparatus. The addition of the label, which was mentioned above, is carried out with the participation of two enzymes. The specific recognition of lysosomal hydrolases by the elements of their tertiary structure and the addition of N-acetylglucosamine phosphate is carried out by N-acetylglucosamine phosphotransferase. Phosphoglycoside - the second enzyme - cleaves N-acetylglucosamine, resulting in the formation of the M6F-tag. This, in turn, is recognized by a receptor protein. With its help, hydrolases enter the vesicles and send them into lysosomes. In them, in an acidic environment, phosphate is cleaved from the mature hydrolase. In the presence of disturbances in the activity of N-acetylglucosamine phosphotransferase due to mutations or due to genetic defects in the M6F receptor, all lysosomal enzymes are delivered by default to the outer membrane. They are then secreted into extracellular conditions. It was also found that some of the M6P receptors are also transported to the outer membrane. They carry out the return of accidentally trapped lysosomal enzymes from the external environment into the cell during endocytosis.

Transport of substances to the outer membrane

Usually, even at the stage of synthesis, the protein compounds of the outer membrane are embedded in the wall of the endoplasmic reticulum with their hydrophobic sections. Then they are delivered to the Golgi complex. From there, they are transported to the cell surface. In the process of fusion of plasmalemma and vesicles, such compounds are not released into the external environment.

Secretion

Almost all the compounds produced in the cell (both protein and non-protein nature) pass through the Golgi complex. There they fold into secretory vesicles. Thus, in plants with the participation of dictyosomes, material is produced


Opening.

A structure known as the Golgi complex was first discovered in cells

Animals in 1898 by Camillo Golgi, Italian physician and cytologist. A detailed study of this structure was done later using an electron microscope.

The Golgi apparatus is found in the cytoplasm of almost all eukaryotic cells, especially in the secretory cells of animals. In yeast, the Golgi complex is somewhat worse, usually in the form of a special section of the endoplasmic reticulum. The Golgi complex is a stack of flattened membrane sacs, the so-called cisterns, and an associated system of vesicles called Golgi vesicles. At one end of the stack

The sacs are constantly being formed by new cisterns by the fusion of vesicles budding from the smooth endoplasmic reticulum. At the other end of the stack, on the inner side, the maturation of the cisterns is completed and they again disintegrate into bubbles. Thus, the tanks in the stack gradually move from the outside to the inside.

The function of the Golgi apparatus is transport and chemical

sky modification of the substances entering it. The initial substrate for enzymes are proteins that enter the Golgi apparatus from the endoplasmic reticulum. After modification and concentration, the enzymes in the Golgi vesicles are transported to their "destination", for example, to the site of the formation of a new kidney. This transfer is most actively carried out with the participation of cytoplasmic microtubules.

The Golgi apparatus is a component of all eukaryotic cells (practically the only exception is mammalian erythrocytes). He n

is the most important membrane organelle that controls the processes of intracellular transport. The main functions of the Golgi apparatus are modification, accumulation, sorting and direction of various substances into the corresponding intracellular compartments, as well as outside the cell. It consists of a set of flattened cisterns surrounded by a membrane, resembling a stack of plates. Each Golgi stack (called a dictyosome in plants) usually contains four to six cisterns, usually about 1 micron in diameter (Fig. 8-36). The number of Golgi stacks in a cell depends largely on its type: some cells contain one large stack, while others have hundreds of very small stacks.

Golgi stacks are always associated with a mass of small (approximately 60 nm in diameter) vesicles bounded by a membrane. It is believed

That these vesicles (Golgi vesicles) carry proteins and lipids into the Gol'dki apparatus, transport them out of it and between the rest of the cisterns. Many vesicles are bordered and coated with clathrin or another specific protein. Such bordered vesicles can often be seen detaching from the Golgi cisterns.

The Golgi apparatus has two different sides: the emerging, or cis-side, and the mature, or trans-side. The Cis-side is closely related to the transitional elements of the ER; the trans side expands to form a tubular reticulum called the trans Golgi reticulum. Proteins and lipids in small vesicles enter the Golgi stack from the cis side, and leave it, heading to various compartments, along with vesicles that form on the trans side. Passing from one stack of Golge

and in the other, these molecules undergo successive series of modifications.

Structure.

The description of the structure of the Golgi apparatus is closely related to the description of its main biochemical functions, since the subdivision of this cell

compartments into departments is mainly based on the localization of enzymes located in a particular department.

Most often, there are four main divisions in the Golgi apparatus: cis-Golgi, medial-Golgi, trans-Golgi, and trans-Golgi network (TGN)

In addition, the so-called intermediate compartment is sometimes referred to as the Golgi apparatus, which is an accumulation of membrane vesicles between the endoplasmic reticulum and the cis-Golgi. The Golgi apparatus is a highly polymorphic organelle; in cells of different types and even at different stages of development of the same cell, it may look different. Its main characteristics are as follows:

  1. the presence of a stack of several (usually 3-8) flattened cisterns, more or less tightly adjacent to each other. Such a stack is always surrounded by some (sometimes very significant) number of membrane vesicles. In animal cells one can often find one stack, while in plant cells there are usually several; each of them is then called a dictyosome. Individual dictyosomes can be interconnected by a system of vacuoles, forming a three-dimensional network;
  2. compositional heterogeneity, expressed in the fact that resident enzymes are heterogeneously distributed over the organelle;
  3. polarity, that is, the presence of the cis side facing the endoplasmic reticulum and the nucleus, and the trans side facing the cell surface (this is especially characteristic of secreting cells);
  4. association with microtubules and centriole region. The destruction of microtubules by depolymerizing agents leads to fragmentation of the Golgi apparatus, but its functions are not significantly affected. A similar fragmentation is observed in vivo, during mitosis. After the restoration of the microtubule system, the elements of the Golgi apparatus scattered over the cell are collected (along the microtubules) in the centriole region, and the normal Golgi complex is reconstructed.

The Golgi apparatus (Golgi complex) is a membrane structure of a eukaryotic cell, mainly intended for the excretion of substances synthesized in the endoplasmic reticulum. The Golgi complex was named after the Italian scientist Camillo Golgi, who first discovered it in 1898.

The Gol'dka complex is a stack of disc-shaped membrane sacs (cisterns), somewhat expanded closer to the edges, and the Gol'dka vesicle system associated with them. A number of separate stacks (dictyosomes) are found in plant cells; animal cells often contain one large or several stacks connected by tubes.

In the tanks of the Golgi Apparatus, proteins intended for secretion, transmembrane proteins of the plasma membrane, proteins of lysosomes, etc. mature. Ripening proteins sequentially move along the cisterns of the organelle, in which their final folding occurs, as well as modifications - glycosylation and phosphorylation.

The Golgi apparatus is asymmetric - the cisterns located closer to the cell nucleus (cis-Golgi) contain the least mature proteins, membrane vesicles - vesicles budding from the granular endoplasmic reticulum (ER) on the membranes of which ribosomes synthesize proteins - are continuously attached to these cisterns.

Different cisterns of the Golgi apparatus contain different resident catalytic enzymes and, consequently, different processes occur with maturing proteins in them. It is clear that such a stepwise process must somehow be controlled. Indeed, maturing proteins are “marked” with special polysaccharide residues (mainly mannose), apparently playing the role of a kind of “quality mark”.

It is not completely clear how the maturing proteins move along the cisterns of the Golgi apparatus, while the resident proteins remain more or less associated with one cistern. There are two mutually exclusive hypotheses explaining this mechanism. According to the first (1), proteins are transported using the same mechanisms of vesicular transport as the transport pathway from the ER, and resident proteins are not included in the budding vesicle. According to the second (2), there is a continuous movement (maturation) of the cisterns themselves, their assembly from vesicles from one end and disassembly from the other end of the organelle, and resident proteins move retrogradely (in the opposite direction) using vesicular transport.

Eventually, vesicles containing fully mature proteins bud from the opposite end of the organelle (trans-Golgi).

The Golgi complex is

1. O-glycosylation, complex sugars are attached to proteins through the oxygen atom.

2. Phosphorylation (addition of phosphoric acid residue to proteins).

3. Lysosome formation.

4. Cell wall formation (in plants).

5. Participation in vesicular transport (formation of a three-protein flow):

6. maturation and transport of plasma membrane proteins;

7. maturation and transport of secrets;

8. maturation and transport of lysosome enzymes.

The Golgi apparatus (Golgi complex) is a specialized part of the endoplasmic reticulum, consisting of stacked flat membrane sacs. It is involved in the secretion of proteins by the cell (the secreted proteins are packed into granules in it) and therefore is especially developed in cells that perform a secretory function. The important functions of the Gol'dka apparatus also include the attachment of carbohydrate groups to proteins and the use of these proteins to build the cell membrane and the membrane of lysosomes. In some algae, cellulose fibers are synthesized in the Golgi apparatus.

Functions.

The function of the Golgi apparatus is transport and chemical modification of substances entering it. The initial substrate for enzymes are proteins that enter the Golgi apparatus from the endoplasmic reticulum. After modification and concentration, the enzymes in the Golgi vesicles are transported to their "destination", for example, to the site of the formation of a new kidney. This transfer is most actively carried out with the participation of cytoplasmic microtubules.

The functions of the Golgi apparatus are very diverse. These include:

1) sorting, accumulation and excretion of secretory products;

2) completion of post-translational protein modification (glycosylation, sulfation, etc.);

3) the accumulation of lipid molecules and the formation of lipoproteins;

4) the formation of lysosomes;

5) the synthesis of polysaccharides for the formation of glycoproteins, waxes, gums, mucus, matrix substances of plant cell walls

(hemicellulose, pectins), etc.

6) the formation of a cell plate after nuclear division in plant cells;

7) participation in the formation of the acrosome;

8) the formation of contractile protozoan vacuoles.

This list is undoubtedly incomplete, and further research will not only allow a better understanding of the already known functions of the Golgi apparatus, but will also lead to the discovery of new ones. So far, the most studied from the biochemical point of view are the functions associated with the transport and modification of newly synthesized proteins.

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 located 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 being separated from the Golgi apparatus, become lysosomes themselves. 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 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 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 (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 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 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 (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 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. 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 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. 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"

The Golgi complex is located near the nucleus following the EPR and often near the centriole, formed by a stack of 3-10 flattened and slightly curved cisterns with widened ends. Place of maturation and sorting of proteins.

In many animal cells, for example in nerve cells, it takes the form of a complex network located around the nucleus. In the cells of plants and protozoa, the Golgi complex is represented by individual crescent or rod-shaped bodies. The structure of this organoid is similar in the cells of plant and animal organisms, despite the diversity of its shape.

The Golgi complex includes: cavities bounded by membranes and located in groups (5-10 each); large and small bubbles located at the ends of the cavities. All these elements make up a single complex.

Cisterns to. G. form three main compartments: cis-side, trans-side, intermediate compartment. With K.G.

18. Golgi complex, its structure and functions. Lysosomes. Their structure and function. Types of lysosomes.

closely related and always considered together the trans Golgi network.

The cis side (forming) includes cisterns facing the expanded elements of the granular endoplasmic reticulum, as well as small transport vesicles.

The trans-side (mature) is formed by cisterns facing vacuoles and secretory granules. At a short distance from the regional cistern lies the G.

The intermediate compartment contains a small number of cisterns between the cis and trans sides.

Functions of the Golgi complex

1. Modification of the secretory product: enzymes K.G. glycosylate proteins and lipids, the glycoproteins formed here, proteoglycans, glycolipids and sulfated glycosaminoglycans are intended for subsequent secretion.

2. Concentration of secretory products occurs in condensing vacuoles located on the trans side.

3.Packaging of the secretory product, the formation of secretory granules involved in exocytosis.

4. Sorting and packaging of the secretory product, the formation of secretory granules.

The Golgi complex has many important functions. The products of the cell's synthetic activity - proteins, carbohydrates and fats - are transported to it through the channels of the endoplasmic reticulum. All these substances first accumulate, and then in the form of large and small bubbles enter the cytoplasm and are either used in the cell itself in the course of its life, or are removed from it and used in the body. For example, digestive enzymes are synthesized in the cells of the mammalian pancreas, which accumulate in the cavities of the organoid. Then vesicles filled with enzymes are formed. They are removed from the cells into the pancreatic duct, from where they flow into the intestinal cavity. Another important function of this organelle is that fats and carbohydrates (polysaccharides) are synthesized on its membranes, which are used in the cell and which are part of the membranes. Thanks to the activity of the Golgi complex, the renewal and growth of the plasma membrane occurs.

The Golgi complex is involved in the accumulation of products synthesized in the endoplasmic reticulum, in their chemical rearrangement and maturation. In the tanks of the Golgi complex, the synthesis of polysaccharides takes place, their complexation with protein molecules. One of the main functions of the Golgi complex is the formation of finished secretory products that are removed from the cell by exocytosis. The most important functions of the Golgi complex for the cell are also the renewal of cell membranes, including the areas of the plasmolemma, as well as the replacement of plasmolemma defects in the process of the secretory activity of the cell. The Golgi complex is considered the source of the formation of primary lysosomes, although their enzymes are also synthesized in the granular network.

Golgi complex is a stack of membrane sacs (cisterns) and a system of vesicles associated with it.

On the outer, concave side of a stack of bubbles budding from smooth. EPS, new tanks are constantly being formed, and on the inside of the tank they turn back into bubbles.

The main function of the Golgi complex is the transport of substances into the cytoplasm and the extracellular environment, as well as the synthesis of fats and carbohydrates. The Golgi complex is involved in the growth and renewal of the plasma membrane and in the formation of lysosomes.

The Golgi complex was opened in 1898 by K. Golgi. With extremely primitive equipment and a limited set of reagents, he made a discovery, thanks to which, together with Ramon-i-Cajal, he received the Nobel Prize. He treated nerve cells with a solution of dichromate, after which he added silver nitrates and osmium. Using the precipitation of osmium or silver salts with cellular structures, Golgi discovered a dark-colored network in neurons, which he called the internal mesh apparatus. When dyed by general methods, the lamellar complex does not accumulate dyes, therefore, the zone of its concentration is visible as a light area. For example, near the nucleus of the plasmacyte, a light zone is visible, corresponding to the region of the organelle.

Most often, the Golgi complex is adjacent to the nucleus. With light microscopy, it can be distributed in the form of complex networks or separate diffusely located areas (dictyosomes). The shape and position of the organelle are not of fundamental importance and can change depending on the functional state of the cell.

The Golgi complex is a place of condensation and accumulation of secretion products produced in other parts of the cell, mainly in the EPS. During protein synthesis, radioisotope-labeled amino acids accumulate in gr. EPS, and then they are found in the Golgi complex, secretory inclusions, or lysosomes. This phenomenon makes it possible to determine the significance of the Golgi complex in synthetic processes in the cell.

Electron microscopy shows that the Golgi complex consists of clusters of flat cisterns called dictyosomes. The tanks are tightly adjacent to each other at a distance of 20 ... 25 nm. The lumen of the cisterns in the central part is about 25 nm, and extensions form at the periphery - ampoules, the width of which is variable. Each stack contains about 5 ... 10 tanks. In addition to densely spaced flat cisterns, the Golgi complex contains a large number of small vesicles (vesicles), especially along the edges of the organelle. Sometimes they are detached from the ampoules.

On the side adjacent to the EPS and the nucleus, the Golgi complex contains a zone containing a significant number of small vesicles and small cisterns.

The Golgi complex is polarized, that is, it is qualitatively heterogeneous from different sides.

Golgi apparatus

It has an immature cis surface lying closer to the nucleus, and a mature trans surface facing the cell surface. Accordingly, an organelle consists of several interconnected compartments that perform specific functions.

The cis compartment is usually facing the cell center. Its outer surface is convex. Microvesicles (transport pinocytosis vesicles), heading from the EPS, merge with the cisterns. The membranes are constantly renewed by bubbles and, in turn, replenish the contents of the membrane formations of other compartments. In the compartment, post-translational processing of proteins begins, which continues in the next parts of the complex.

The intermediate compartment carries out glycosylation, phosphorylation, carboxylation, sulfation of biopolymer protein complexes. The so-called post-translational modification of polypeptide chains occurs. Glycolipids and lipoproteins are being synthesized. In the intermediate compartment, as in the cis compartment, tertiary and quaternary protein complexes are formed.

Some proteins undergo partial proteolysis (destruction), which is accompanied by their transformation necessary for maturation. Thus, cis and intermediate compartments are required for the maturation of proteins and other complex biopolymer compounds.

The trans compartment is located closer to the cell periphery. Its outer surface is usually concave. Partially, the trans-compartment passes into the trans-network - a system of vesicles, vacuoles and tubules.

In cells, individual dictyosomes can be connected to each other by a system of vesicles and cisterns adjacent to the distal end of an accumulation of flat sacs, so that a loose three-dimensional network is formed - a trans-network.

In the structures of the trans-compartment and trans-network, sorting of proteins and other substances occurs, the formation of secretory granules, precursors of primary lysosomes and vesicles of spontaneous secretion. The secretory vesicles and prelisosomes are surrounded by proteins - clathrins.

Clathrins are deposited on the membrane of the forming vesicle, gradually splitting it off from the distal cistern of the complex. Bordered vesicles depart from the trans-network, their movement is hormone-dependent and controlled by the functional state of the cell. The process of transporting bordered vesicles is influenced by microtubules. Protein (clathrin) complexes around the vesicles disintegrate after the vesicle cleaves from the trans-network and are re-formed at the time of secretion. At the time of secretion, the protein complexes of the vesicles interact with the proteins of the microtubules, and the vesicle is transported to the outer membrane. Vesicles of spontaneous secretion are not surrounded by clathrins, their formation occurs continuously and they, heading towards the cell membrane, merge with it, ensuring the restoration of the cytolemma.

In general, the Golgi complex is involved in segregation - this is separation, separation of certain parts from the bulk, and the accumulation of products synthesized in EPS, in their chemical rearrangements, maturation. In the tanks, the synthesis of polysaccharides takes place, their combination with proteins, which leads to the formation of complex complexes of peptidoglycans (glycoproteins). With the help of the elements of the Golgi complex, ready-made secretions are removed outside the secretory cell.

Small transport bubbles are split off from gr. EPS in ribosome-free zones. The bubbles restore the membranes of the Golgi complex and deliver polymer complexes synthesized in EPS to it. The bubbles are transported to the cis compartment, where they merge with its membranes. Consequently, new portions of membranes and products synthesized in gr. Enter the Golgi complex. EPS.

In the tanks of the Golgi complex, secondary changes occur in the proteins synthesized in gr. EPS. These changes are associated with the rearrangement of the oligosaccharide chains of glycoproteins. Inside the cavities of the Golgi complex, lysosomal proteins and secretion proteins are modified with the help of transglucosidases: there is a sequential replacement and build-up of oligosaccharide chains. The modified proteins pass from the cis-compartment cistern to the trans-compartment cistern due to transport in the vesicles containing the protein.

In the trans-compartment, proteins are sorted: protein receptors are located on the inner surfaces of the cistern membranes, which recognize secretory proteins, membrane proteins and lysosomes (hydrolases). As a result, three types of small vacuoles are cleaved from the distal trans-parts of dictyosomes: containing hydrolases - prelisosomes; with secretory inclusions, vacuoles that replenish the cell membrane.

The secretory function of the Golgi complex is that the exported protein synthesized on the ribosomes, separated and accumulated inside the EPS cisterns, is transported to the vacuole of the lamellar apparatus. Then the accumulated protein can condense, forming secretory protein granules (in the pancreas, mammary and other glands), or remain dissolved (immunoglobulins in plasma cells). Vesicles containing these proteins are cleaved from the ampullar expansion of the Golgi complex cisterns. Such bubbles can merge with each other, increase in size, forming secretory granules.

After that, the secretory granules begin to move to the cell surface, come into contact with the plasmolemma, with which their own membranes merge, and the contents of the granules are outside the cell. Morphologically, this process is called extrusion, or excretion (ejection, exocytosis) and resembles endocytosis, only with the reverse sequence of stages.

The Golgi complex can sharply increase in size in cells that actively carry out a secretory function, which is usually accompanied by the development of EPS, and in the case of protein synthesis, the nucleolus.

During cell division, the Golgi complex disintegrates into separate cisterns (dictyosomes) and / or vesicles, which are distributed between two dividing cells and at the end of the telophase restore the structural integrity of the organelle. Outside of division, there is a continuous renewal of the membrane apparatus due to vesicles migrating from the EPS and distal cisterns of the dictyosome due to the proximal compartments.

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Golgi complex: description

How the Golgi apparatus works

Golgi apparatus (Golgi complex) - AG

The structure known today as complex or Golgi apparatus (AG) first discovered in 1898 by the Italian scientist Camillo Golgi

It was possible to study in detail the structure of the Golgi complex much later using an electron microscope.

AG 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.

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

Golgi complex

On the left - in a cage, among other organelles.

On the right - the Golgi complex with membrane vesicles separating from it

All substances synthesized on EPS membranes carried over to Golgi complex v membrane vesicles, which bud off from the EPS and then merge with the Golgi complex. The incoming organic matter from EPS undergoes further biochemical transformations, accumulates, and is packed into membrane vesicles and delivered to the places in the cage where they are needed. They are involved in the completion cell membrane or stand out outward ( secreted) from the cell.

Functions of the Golgi apparatus:

1 Participation in the accumulation of products synthesized in the endoplasmic reticulum, in their chemical rearrangement and maturation. In the tanks of the Golgi complex, the synthesis of polysaccharides takes place, their complexation with protein molecules.

2) Secretory - the formation of finished secretory products that are removed outside the cell by exocytosis.

3) Renewal of cell membranes, including areas of the plasmolemma, as well as replacement of plasma membrane defects in the process of cell secretory activity.

4) Place of formation of lysosomes.

5) Transport of substances

Lysosomes

The lysosome was discovered in 1949 by C. de Duve (Nobel Prize for 1974).

Lysosomes- one-membrane organelles. They are small bubbles (diameter from 0.2 to 0.8 microns) containing a set of hydrolytic enzymes - hydrolases. The lysosome can contain from 20 to 60 different types of hydrolytic enzymes (proteinases, nucleases, glucosidases, phosphatases, lipases, etc.) that break down various biopolymers. The breakdown of substances using enzymes is called lysis (lysis-disintegration).

Lysosomal enzymes are synthesized on a rough EPS, move to the Golgi apparatus, where they are modified and packed into membrane vesicles, which, after being separated from the Golgi apparatus, become lysosomes proper. (Lysosomes are sometimes called the "stomachs" of the cell)

Lysosome - membrane vesicle containing hydrolytic enzymes

Functions of lysosomes:

1. Degradation of substances absorbed as a result of phagocytosis and pinocytosis. Biopolymers are broken down to monomers, which enter the cell and are used for its needs. For example, they can be used to synthesize new organic substances, or they can be further degraded to generate energy.

2. Destroy old, damaged, excess organelles. The destruction of organelles can also occur during cell starvation.

3. Carry out autolysis (self-destruction) of cells (liquefaction of tissues in the area of ​​inflammation, destruction of cartilage cells during the formation of bone tissue, etc.).

Autolysis - this is self-destruction cells resulting from the release of contents lysosomes inside the cell. Thanks to this, lysosomes are jokingly called "Instruments of suicide." Autolysis is a normal phenomenon of ontogenesis, it can spread both to individual cells and to the entire tissue or organ, as it happens during the resorption of the tadpole's tail during metamorphosis, i.e., when the tadpole turns into a frog

Endoplasmic reticulum, Golgi apparatus and lysosomesform a single vacuolar system of the cell, the individual elements of which can pass into each other during the restructuring and change in the function of the membranes.

Mitochondria

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

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 limited two membranes ... The outer membrane of mitochondria is smooth, the inner membrane forms numerous folds - crista. Crystals increase the surface area of ​​the inner membrane. The number of cristae in mitochondria can vary depending on the cell's energy requirements. It is on the inner membrane that numerous enzyme complexes are concentrated that participate in the synthesis of adenosine triphosphate (ATP). Here, the energy of chemical bonds is converted into energy-rich (high-energy) ATP bonds ... Besides, in the mitochondria, the breakdown of fatty acids and carbohydrates takes place with the release of energy, which is accumulated and used for the processes of growth and synthesis The internal environment of these organelles is called matrix... It contains circular DNA and RNA, small ribosomes. It is interesting that mitochondria are semi-autonomous organelles, since they depend on the functioning of the cell, but at the same time they can maintain a certain independence. So, they are able to synthesize their own proteins and enzymes, as well as reproduce on their own (mitochondria contain their own DNA chain, which contains up to 2% of the DNA of the cell itself).

Mitochondrial functions:

1. Conversion of the energy of chemical bonds into high-energy ATP bonds (mitochondria are the "energy stations" of the cell).

2. Participate in the processes of cellular respiration - oxygen breakdown of organic substances.

Ribosomes

Ribosome structure:
1 - large subunit; 2 - small subunit.

Ribosomes - non-membrane organelles, about 20 nm in diameter. Ribosomes are composed of two fragments - large and small subunits. The chemical composition of ribosomes is proteins and rRNA. RRNA molecules make up 50–63% of the ribosome mass and form its structural framework.

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.

Subunits of ribosomes are formed in the nucleolus. Having passed through the pores in the nuclear envelope, ribosomes enter the membranes of the endoplasmic reticulum (EPS).

Ribosome function: assembly of the polypeptide chain (synthesis of protein molecules from amino acids).

Cytoskeleton

Cellular cytoskeleton is formed microtubules and microfilaments .

Microtubules are cylindrical formations with a diameter of 24 nm. Their length is 100 μm-1 mm. The main component is a protein called tubulin. It is unable to contract and can be destroyed by colchicine.

Microtubules are located in the hyaloplasm and perform the following functions:

  • create an elastic, but at the same time, strong frame of the cell, which allows it to maintain its shape;
  • take part in the process of distribution of cell chromosomes (form a spindle of division);
  • provide movement of organelles;
  • contained in the cell center, as well as in flagella and cilia.

Microfilaments- filaments that are located under the plasma membrane and consist of the protein actin or myosin. They can contract, resulting in the movement of the cytoplasm or protrusion of the cell membrane. In addition, these components are involved in the formation of constrictions during cell division.

Cell center

The cell center is an organoid consisting of 2 small granule centrioles and a radiant sphere around them - the centrosphere. The centriole is a cylindrical body 0.3-0.5 microns long and about 0.15 microns in diameter. The walls of the cylinder are composed of 9 parallel tubes. The centrioles are arranged in pairs at right angles to each other. The active role of the cell center is found during cell division. 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.

Centrioles belong to self-reproducing organelles of the cytoplasm, they arise as a result of duplication of existing centrioles.

Functions:

1. Ensuring a uniform divergence of chromosomes to the poles of the cell during mitosis or meiosis.

2. Center for the organization of the cytoskeleton.

Movement organelles

Not present in all cells

Organoids of movement include cilia, as well as flagella. These are miniature hair-like outgrowths. The flagellum contains 20 microtubules. Its base is located in the cytoplasm and is called the basal body. The length of the flagellum is 100 µm or more. Flagella, which have only 10-20 microns, are called cilia ... When the microtubules slide, the cilia and flagella are able to vibrate, causing the cell itself to move. The cytoplasm may contain contractile fibrils called myofibrils. Myofibrils, as a rule, are located in myocytes - cells of muscle tissue, as well as in the cells of the heart. They are composed of smaller fibers (protofibrils).

In animals and humans cilia they cover the airways and help get rid of fine particulate matter such as dust. In addition, there are also pseudopods, which provide amoeboid movement and are elements of many unicellular and animal cells (for example, leukocytes).