Golgi complex protein synthesis. Golgi complex. Structure of the Golgi complex. Lysosomes. Golgi complex: structure

Structure of the Golgi complex

Golgi complex (KG), or internal mesh apparatus , is a special part of the metabolic system of the cytoplasm, participating in the process of isolation and formation of membrane structures of the cell.

CG is visible in an optical microscope as a mesh or curved rod-shaped bodies lying around the nucleus.

Under an electron microscope, it was revealed that this organelle is represented by three types of formations:

All components of the Golgi apparatus are formed by smooth membranes.

Note 1

Occasionally, AG has a granular-mesh structure and is located near the nucleus in the form of a cap.

AG is found in all cells of plants and animals.

Note 2

The Golgi apparatus is significantly developed in secretory cells. It is especially visible in nerve cells.

The internal intermembrane space is filled with a matrix that contains specific enzymes.

The Golgi apparatus has two zones:

• formation zone, where, with the help of vesicles, the material that is synthesized in the endoplasmic reticulum enters;
• ripening zone, where the secretion and secretory sacs are formed. This secretion accumulates at the terminal sites of the AG, from where secretory vesicles bud. As a rule, such vesicles carry secretions outside the cell.

• Localization of CG

In apolar cells (for example, in nerve cells), the CG is located around the nucleus; in secretory cells, it occupies a place between the nucleus and the apical pole.

The Golgi sac complex has two surfaces:

formative(immature or regenerative) cis-surface (from the Latin Cis - on this side); functional(mature) – trans-surface (from Latin Trans – through, behind).

The Golgi column with its convex formative surface faces the nucleus, is adjacent to the granular endoplasmic reticulum and contains small round vesicles called intermediate. The mature concave surface of the sac column faces the apex (apical pole) of the cell and ends in large vesicles.

Formation of the Golgi complex

KG membranes are synthesized by the granular endoplasmic reticulum, which is adjacent to the complex. The areas of the EPS adjacent to it lose ribosomes, and small, so-called, ribosomes bud from them. transport or intermediate vesicles. They move to the formative surface of the Golgi column and merge with its first sac. On the opposite (mature) surface of the Golgi complex there is an irregularly shaped sac. Its expansion - prosecretory granules (condensing vacuoles) - continuously buds and turns into vesicles filled with secretion - secretory granules. Thus, to the extent that the membranes of the mature surface of the complex are used for secretory vesicles, the sacs of the formative surface are replenished at the expense of the endoplasmic reticulum.

Functions of the Golgi complex

The main function of the Golgi apparatus is the removal of substances synthesized by the cell. These substances are transported through the cells of the endoplasmic reticulum and accumulate in the vesicles of the reticular apparatus. Then they are either released into the external environment or the cell uses them in the process of life.

The complex also concentrates some substances (for example, dyes) that enter the cell from the outside and must be removed from it.

In plant cells, the complex contains enzymes for the synthesis of polysaccharides and the polysaccharide material itself, which is used to build the cellulose membrane of the cell.

In addition, CG synthesizes those chemicals that form the cell membrane.

In general, the Golgi apparatus performs the following functions:

1. accumulation and modification of macromolecules that were synthesized in the endoplasmic reticulum;
2. formation of complex secretions and secretory vesicles by condensation of the secretory product;
3. synthesis and modification of carbohydrates and glycoproteins (formation of glycocalyx, mucus);
4. modification of proteins - adding various chemical formations to the polypeptide (phosphate - phosphorylation, carboxyl - carboxylation), the formation of complex proteins (lipoproteins, glycoproteins, mucoproteins) and the breakdown of polypeptides;
5. is important for the formation and renewal of the cytoplasmic membrane and other membrane formations due to the formation of membrane vesicles, which subsequently merge with the cell membrane;
6. formation of lysosomes and specific granularity in leukocytes;
7. formation of peroxisomes.

The protein and, partially, carbohydrate contents of CG come from the granular endoplasmic reticulum, where it is synthesized. The main part of the carbohydrate component is formed in the sacs of the complex with the participation of glycosyltransferase enzymes, which are located in the membranes of the sacs.

In the Golgi complex, cellular secretions containing glycoproteins and glycosaminoglycans are finally formed. In the CG, secretory granules mature, which turn into vesicles, and the movement of these vesicles towards the plasma membrane. The final stage of secretion is the pushing of the formed (mature) vesicles outside the cell. The removal of secretory inclusions from the cell is carried out by installing the membranes of the vesicle into the plasmalemma and releasing secretory products outside the cell. In the process of moving secretory vesicles to the apical pole of the cell membrane, their membranes thicken from the initial 5-7 nm, reaching a plasmalemma thickness of 7-10 nm.

Note 4

There is an interdependence between cell activity and the size of the Golgi complex - secretory cells have large columns of CG, while non-secretory cells contain a small number of complex sacs.

The structure and functions of the Golgi complex are associated with the completion of the modification of substances coming from the ER and their redistribution to their destinations.

Animal cells most often have one large Golgi complex, while plant cells have several smaller stacks called dictyosomes.

In terms of its structure, the Golgi apparatus is a stack of membrane disks (with cavities inside). Each such disk is called a tank. Each tank expands towards the edges. In addition to the disks, the apparatus also includes associated vesicular vesicles, as well as (presumably) a surrounding membrane network linking the individual cisterns together.

The side of the Golgi facing the nucleus is called the cis compartment. The side facing the plasmalemma is the trans-compartment. The median section is also distinguished. The enzymatic composition of different departments is different, therefore each of them has its own chemical reactions, i.e. stages of modification of substances. The substance, passing through the tanks as if on a conveyor, gradually acquires the necessary chemical structure and functionality.

From the endoplasmic reticulum, proteins, fats and carbohydrates synthesized there enter the Golgi complex with the help of vesicles (vesicles surrounded by a membrane). At the same time, proteins have signal chemical tags (in the form of oligosaccharides), which “tell” the Golgi complex what to do with them.

This diagram shows how a protein that was synthesized in the ER, passing through the Golgi apparatus, becomes a component of the cell membrane. The protein is indicated here by a green oval. The pink element attached to it represents a carbohydrate bound to a protein. In fact, it is not the protein that is transported and modified, but the glycoprotein (carbohydrate + protein).

The growth of the cytoplasmic membrane is only one of the functions of the Golgi complex. Also, components of the intercellular fluid, the matrix of cell walls (in plants), various secrets (in secretory cells), etc. are released outside the cell by exocytosis.

Another function is the formation of lysosomes - cellular organelles containing mainly enzymes for breaking down complex substances entering the cell.

Transport vesicles are also formed in the Golgi, delivering substances to other cellular organelles.

The Golgi complex, or apparatus, is named after the scientist who discovered it. This cellular organelle looks like a complex of cavities bounded by single membranes. In plant cells and protozoa it is represented by several separate smaller stacks (dictyosomes).

The Golgi complex, in appearance, visible through an electron microscope, resembles a stack of disc-shaped sacs superimposed on each other, around which there are many vesicles. Inside each “bag” there is a narrow channel, expanding at the ends into so-called tanks (sometimes the entire bag is called a tank). Bubbles bud from them. A system of interconnected tubes is formed around the central stack.

On the outer, somewhat convex side of the stack, new cisterns are formed by the fusion of vesicles budding from the smooth endoplasmic reticulum. On the inside of the tank, they complete their maturation and break up again into bubbles. Thus, the Golgi cisterns (stack sacs) move from the outside to the inside.

The part of the complex located closer to the nucleus is called “cis”.

The one closest to the membrane is “trans”.

Functions of the Golgi complex

The functions of the Golgi apparatus are diverse, in total they come down to modification, redistribution of substances synthesized in the cell, as well as their removal outside the cell, the formation of lysosomes and the construction of the cytoplasmic membrane.

The activity of the Golgi complex is high in secretory cells. Proteins coming from the ER are concentrated in the Golgi apparatus and then transferred to the membrane in the Golgi vesicles. Enzymes are secreted from the cell by reverse pinocytosis.

Oligosaccharide chains are attached to the proteins arriving at the Golgi. In the apparatus, they are modified and serve as markers, with the help of which proteins are sorted and directed along their path.

In plants, during the formation of the cell wall, the Golgi secretes carbohydrates that serve as a matrix for it (cellulose is not synthesized here). The budding Golgi vesicles move with the help of microtubules. Their membranes merge with the cytoplasmic membrane, and the contents are included in the cell wall.

The Golgi complex of goblet cells (located deep in the epithelium of the intestinal mucosa and respiratory tract) secretes the glycoprotein mucin, which forms mucus in solutions. Similar substances are synthesized by cells of the root tip, leaves, etc.

In the cells of the small intestine, the Golgi apparatus performs the function of lipid transport. Fatty acids and glycerol enter the cells. In the smooth ER, the synthesis of its lipids occurs. Most of them are coated with proteins and transported to the cell membrane via the Golgi. After passing through it, the lipids end up in the lymph.

An important function is the formation of lysosomes.

Golgi complex is a membrane structure inherent in any eukaryotic cell.

The Golgi apparatus is represented by flattened cisternae (or sacs) collected in a stack. Each tank is slightly curved and has convex and concave surfaces.

The average diameter of the tanks is about 1 micron. In the center of the tank, its membranes are brought closer together, and at the periphery they often form expansions, or ampoules, from which the bubbles are detached. Packets of flat tanks with an average number of about 5-10 form a dictyosome. In addition to the cisternae, the Golgi complex contains transport and secretory vesicles. In the dictyosome, in accordance with the direction of curvature of the curved surfaces of the tanks, two surfaces are distinguished. A convex surface is called an immature or cis surface. It faces the nucleus or the tubules of the granular endoplasmic reticulum and is connected to the latter by vesicles that detach from the granular reticulum and bring protein molecules to the dictyosome for maturation and formation into the membrane. The opposite transsurface of the dictyosome is concave. It faces the plasmalemma and is called mature because secretory vesicles containing secretion products ready for removal from the cell emerge from its membranes.

The Golgi complex is involved in:

• in the accumulation of products synthesized in the endoplasmic reticulum,
• in their chemical restructuring and maturation.

In the tanks of the Golgi complex, polysaccharides are synthesized and complexed with protein molecules.

One of the main functions of the Golgi complex is the formation of finished secretory products that are removed outside the cell by exocytosis. The most important functions of the Golgi complex for the cell are also the renewal of cell membranes, including areas of the plasmalemma, as well as the replacement of defects in the plasmalemma during 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. Lysosomes are intracellularly formed secretory vacuoles filled with hydrolytic enzymes necessary for the processes of phago- and autophagocytosis. At the light-optical level, lysosomes can be identified and the degree of their development in the cell can be judged by the activity of the histochemical reaction to acid phosphatase, a key lysosomal enzyme. By electron microscopy, lysosomes are defined as vesicles bounded by a membrane from the hyaloplasm. Conventionally, there are 4 main types of lysosomes:

• primary,
• secondary lysosomes,
• autophagosomes,
• residual bodies.

Primary lysosomes are small membrane vesicles (their average diameter is about 100 nm), filled with homogeneous fine contents, which are a set of hydrolytic enzymes. About 40 enzymes have been identified in lysosomes (proteases, nucleases, glycosidases, phosphorylases, sulfatases), the optimal mode of action of which is designed for an acidic environment (pH 5). Lysosomal membranes contain special carrier proteins for the transport of hydrolytic cleavage products - amino acids, sugars and nucleotides - from the lysosome to the hyaloplasm. The lysosome membrane is resistant to hydrolytic enzymes.

Secondary lysosomes are formed by the fusion of primary lysosomes with endocytotic or pinocytotic vacuoles. In other words, secondary lysosomes are intracellular digestive vacuoles, the enzymes of which are supplied by primary lysosomes, and the material for digestion is supplied by the endocytic (pinocytotic) vacuole. The structure of secondary lysosomes is very diverse and changes during the hydrolytic breakdown of the contents. Lysosome enzymes break down biological substances that have entered the cell, resulting in the formation of monomers that are transported through the lysosome membrane into the hyaloplasm, where they are utilized or included in a variety of synthetic and metabolic reactions.

If the cell’s own structures (aging organelles, inclusions, etc.) are exposed to interaction with primary lysosomes and hydrolytic cleavage by their enzymes, an autophagosome is formed. Autophagocytosis is a natural process in the life of a cell and plays a large role in the renewal of its structures during intracellular regeneration.

Residual bodies are one of the final stages of the existence of phago- and autolysosomes and are found during incomplete phago- or autophagocytosis and are subsequently released from the cell by exocytosis. They have compacted contents, and secondary structuring of undigested compounds is often observed (for example, lipids form complex layered formations).

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Functions of the Golgi complex

1. Synthesis of polysaccharides and glycoproteins (glycocalyx, mucus).

2. Processing of molecules:

a) terminal glycosylation

b) phosphorylation

c) sulfation

d) proteolytic cleavage (parts of protein molecules)

3. Condensation of the secretory product.

4. Packaging of the secretory product

5. Sorting of proteins in the trans-Golgi network area (due to specific receptor membrane proteins that recognize signal sites on macromolecules and direct them to the corresponding vesicles). Transport from the Golgi complex occurs in the form of 3 streams:

1. Hydrolase vesicles (or primary lysosomes)

2. Into the plasmalemma (as part of bordered bubbles)

3. In secretory granules

Endosomes - membrane vesicles with acidifying contents and ensuring the transfer of molecules into the cell. The type of substance transfer by the endosome system is different:

1. With digestion of macromolecules (complete)

With their partial splitting

3. No change during transport

The process of transport and subsequent breakdown of substances in the cell using endosomes consists of the following sequential components:

1. Early(peripheral) endosome

2. Late(perinuclear) endosome prelysosomal stage of digestion

3. Lysosome

Early endosome– a vesicle lacking clathrin at the cell periphery. The pH of the environment is 6.0, a limited and regulated process of cleavage occurs here (the ligand is separated from the receptor) - the return of the receptors to the cell membrane. The early endosome is also known as Curl.

Late (perinuclear) endosome: a) more acidic content pH 5.5

b) larger diameter up to 800 nm

c) deeper level of digestion

This digestion of the ligand (peripheral endosome + perinuclear endosome) is a multivesicular body.

Lysosomes

1. Phagolysosome– it is formed by the fusion of a late endosome or lysosome with a phagosome. The process of destruction of this material is called heterophagy.

2.Autophagolysosome– it is formed by the fusion of a late endosome or lysosome with an autophagosome.

3. Multivesicular body– a large vacuole (800 nm), consisting of small 40-80 nm vesicles surrounded by a moderately dense matrix. It is formed as a result of the fusion of early and late endosomes.

4. Residual bodies- This is undigested material. The most famous component of this type is lipofuscin granules - vesicles of dia. 0.3 – 3 µm, containing lipofuscin pigment.

Cytoskeleton is a system of microtubules, microfilaments (intermediate, microtrabeculae). They all form a three-dimensional network, interacting with networks of other components.

1. Microtubules– hollow cylinders dia. 24-25 nm, wall thickness 5 nm, dia. lumen – 14-15 nm. The wall consists of helically arranged filaments (they are called protofilaments) 5 nm thick. These threads are formed by dimers of tubulin. This is a labile system in which one end (denoted “__”) is fixed, and the other (“+”) is free and participates in the depolymerization process.

Microtubules are associated with a number of proteins, which have the general name MAP - they connect microtubules with other cytoskeletal elements and organelles. Kinesin – (the step of its movement along the surface of the microtubule is 8 nm).

Organelle

rice. Microtubule

Microfilaments– these are two intertwined filaments of F-actin, composed of g-actin. Their diameter is 6 nm. Microfilaments are polar; g-actin attaches at the (“+”) end. They form clusters

along the cell periphery and are connected to the plasma membrane through intermediate proteins (actin, vinculin, talin).

Function: 1. Change in cytosol (transition from sol to gel and back).

2. Endocytosis and exocytosis.

3. Motility of non-muscle cells.

4. Stabilization of local protrusions of the plasma membrane.

Intermediate threads have d 8-11 nm, consist of proteins characteristic of certain cell types. They form an intracellular framework that ensures cell elasticity and the ordered arrangement of cytoplasmic components. Intermediate filaments are formed by thread-like protein molecules woven together like a rope.

Functions: 1. Structural

2. Participation in the formation of the horny substance

3. Maintaining the shape and processes of nerve cells

4. Attachment of myofibrils to the plasmalemma.

Microtrabeculae- an openwork network of thin filaments that exists in combination with microtubules and can participate in the transport of organelles and influence the viscosity of the cytosol.

LECTURE

TOPIC: “CORE. STRUCTURE OF THE INTERPHASE NUCLEUS. BASICS OF BIOSYNTHETIC ACTIVITY OF CELLS”

Core is the main part of the cell that encodes information about the structure and function of the organ. This information is contained in the genetic material, DNA, which is a complex of DNP with the main proteins (histones). With some exceptions (mitochondria), DNA is localized exclusively in the nucleus. DNA is capable of replicating itself, thereby ensuring the transmission of the genetic code to daughter cells under conditions of cell division.

The nucleus plays a central role in the synthesis of proteins and polypeptides, being the carrier of genetic information. All the nuclei of the body's cells contain the same genes; some cells are different in their structure, function and the nature of the substances produced by the cell. Nuclear control is carried out by

repression or depression (expression) of the activity of various genes. Translation about the nature of protein synthesis is associated with the formation of m-RNA. Many RNAs are a complex of protein and RNA, i.e. RNP. The interphase nucleus in most cells is a round or oval formation several mm in diameter. In leukocytes and connective tissue cells, the nucleus is lobulated and is referred to as polymorphic.

Interphase nucleus has several different structures: nuclear envelope, chromatin, karyolymph and nucleolus.

Nuclear envelope

1. Outer nuclear membrane– ribosomes are located on the surface, where proteins are synthesized and enter the perinuclear cisterns. On the cytoplasmic side, it is surrounded by a loose network of intermediate (vimentin) filaments.

2. Perinuclear cisterns– part of the perinuclear cisterns is associated with the granular endoplasmic reticulum (20-50 nm).

3. Inner nuclear membrane – separated from the contents of the nucleus by the nuclear lamina.

4. Nuclear lamina 80-300 nm thick, participates in the organization of the nuclear membrane and perinuclear chromatin, contains intermediate filament proteins - lamins A, B and C.

5. Nuclear time– from 3-4 thousand specialized communications, carry out transport between the nucleus and the cytoplasm. Nuclear pore d 80 nm, has: a) pore channel – 9 nm

b) nuclear pore complex, the latter contains a receptor protein that responds to nuclear import signals (entry ticket to the nucleus). The diameter of the nuclear pore can increase the diameter of the pore channel and ensure the transfer of large macromolecules into the nucleus (DNA-RNA polymerase).

Nuclear time consists of 2 parallel rings, one on each surface of the karyolemma. A ring with a diameter of 80 nm, they are formed by 8 protein granules, from each granule a thread (5 nm) stretches towards the center, which forms a partition (diaphragm). In the center there is a central granule. The set of these structures is called nuclear pore complex. A channel with a diameter of 9 nm is formed here; such a channel is called a water channel, since small water-soluble molecules and ions move through it.

Functions of the nuclear pore: 1. Selective transport;

2. Active transfer into the nucleus of proteins with a sequence characteristic of proteins of nuclear localization;

3. Transfer of ribosomal subunits into the cytoplasm with a change in the conformation of the pore complex.

Inner nuclear membrane- smooth and connected with the help of integral proteins to the nuclear lamina, which is a layer 80-300 nm thick. This record or lamina– consists of intertwined intermediate filaments (10 nm) that form the karyoskeleton. Its functions:

1. Preservation of the structural organization of pore complexes;

2. Maintaining the shape of the core;

3. Ordered chromatin packing.

It is formed as a result of spontaneous association of 3 main polypeptides. This is the structural framework of the nuclear envelope with sites for specific chromatin binding.

Golgi apparatus

Chapter 1. Golgi apparatus: structure and functions

Golgi apparatus

1.1. Golgi apparatus: structure

The description of the structure of the Golgi apparatus is closely related to the description of its basic biochemical functions, since the division of this cellular compartment into sections is carried out mainly on the basis of the localization of enzymes...

Golgi apparatus

1.2. Golgi apparatus: functions

The function of the Golgi apparatus is the transport and chemical modification of substances entering it. The initial substrate for enzymes are proteins entering the Golgi apparatus from the endoplasmic reticulum...

Golgi apparatus

Chapter 2. Analysis of the activity of the Golgi apparatus in the cell

Golgi apparatus

2.1. Analysis of the activity of the Golgi apparatus in the cell

Lysosomes are small vesicles surrounded by a single membrane. They bud from the Golgi apparatus and possibly from the endoplasmic reticulum. Lysosomes contain a variety of enzymes that break down large molecules...

Golgi apparatus

2.3. Golgi apparatus: protein sorting and signal transduction

The Golgi complex functions at the intersection of secretory pathways, receiving newly synthesized proteins and lipids from the ER, covalently modifying them, and then sorting reaction products according to their destinations (Fig. 1gg)...

Golgi apparatus

2.3. Golgi apparatus: molecular mechanism of functioning

A heptameric cytosolic protein complex called COPI (Golgi membrane complex, coatomer), in conjunction with the GTP-binding protein ARF 1, forms an envelope in such a way that, when associated with Golgi membranes...

Genitourinary apparatus

1. Genitourinary apparatus

The genitourinary apparatus consists of the urinary organs, which ensure the formation and removal of urine from the body and the genital organs, which carry out the function of reproduction. Functionally they are in no way connected with each other...

Structural features of birds

Digestive apparatus

The structure of the digestive system of birds is in many ways similar to the digestive apparatus of mammals. It includes the oropharynx, esophagogastric region, small and large intestines. The nature of solid feed processing...

Structural features of birds

Breathing apparatus

The respiratory organs of birds have a number of features: small size and simple structure of the nasal cavity; the presence in the bifurcation of the trachea of ​​a device for producing sound - the singing larynx; insignificant size and position of the lungs...

Structural features of birds

Urinary apparatus

The urinary system consists only of the kidneys and ureters, which open into the urodeum of the cloaca.

The pelvis, bladder, and urethra are absent in birds...

Structural features of birds

Reproduction apparatus

The reproductive organ system ensures the continuation of the species. In farm birds, it also determines egg production. This system consists of the gonads (testes or ovaries), in which sex cells are formed...

The role of the visual analyzer in the life of animals

1.4 Oculomotor apparatus

The eye can be thought of as an optical camera. To point such a “camera” at the object in question (fixation point), it should be rotated. To move the eyeball, there is an oculomotor apparatus...

Photodynamic effect and photodynamic therapy

10. Golgi apparatus and endoplasmic reticulum

Hydrophobic photosensitizers, such as hypericin, Pc 4 phthalocyanine, zinc phthalocyanine or Photofrin, usually accumulate in the perinuclear region, rich in membrane organelles - mitochondria, ER...

Lepidoptera of the European part of Russia with a diurnal lifestyle

3.1.1 Mouthparts

The oral apparatus of Lepidoptera arose through the specialization of ordinary arthropod limbs. Absorption and grinding of food. The mouthparts of butterflies are no less a characteristic feature than the structure of the wings and the scales covering them...

The Golgi apparatus is a stack of flattened membrane sacs (“”) and a system of vesicles associated with them. When studying ultrathin sections, it was difficult to reveal its three-dimensional structure, but scientists suggested that interconnected tubes were formed around the central one.

The Golgi apparatus performs the function of transporting substances and chemical modification of cellular products entering it. This function is especially important in secretory cells, for example, pancreatic acinar cells secrete digestive enzymes of pancreatic juice into the excretory duct. Scientists studied the functioning of the Golgi apparatus using electron micrographs of such a cell. Individual transport of substances was identified using radioactively labeled amino acids.

In a cell, proteins are built from amino acids. It has been established that they are concentrated in the vesicles of the Golgi apparatus and then transported to the plasma membrane. At the final stage, the secretion of inactive enzymes occurs; this form is necessary so that they cannot destroy the cells in which they are formed. Typically, proteins entering the Golgi complex are glycoproteins. There they undergo a modification that turns them into markers that allow the protein to be directed strictly to its intended purpose. Exactly how the Golgi complex distributes molecules has not been precisely established.

Function of carbohydrate secretion

In some cases, the Golgi apparatus takes part in the secretion of carbohydrates, for example, in plants - in the formation of cell wall material. Its activity increases in the region of the cell plate, located between two newly formed daughter nuclei. Golgi vesicles are guided to this site by microtubules. The membranes of the vesicles become part of the plasma membranes of the daughter cells. Their contents become necessary for the construction of cell walls of the middle plate and new walls. Cellulose is supplied separately to cells using microtubules, bypassing the Golgi apparatus.

The Golgi apparatus also synthesizes the glycoprotein mucin, which forms mucus in solution. It is produced by goblet cells, which are located in the thickness of the epithelium of the respiratory tract mucosa and intestinal lining. In some insectivorous plants, the Golgi apparatus produces enzymes and sticky mucus in the leaf glands. The Golgi complex is also involved in the secretion of wax, mucus, gum and plant glue.

The cell is an integral system

A living cell is a unique, perfect, smallest unit of the body; it is designed to use oxygen and nutrients as efficiently as possible while performing its functions. Vital organelles for the cell are the nucleus, ribosomes, mitochondria, endoplasmic reticulum, and Golgi apparatus. Let's talk about the latter in more detail.

What it is

This membrane organelle is a complex of structures that remove substances synthesized in it from the cell. Most often it is located close to the outer cell membrane.

Golgi apparatus: structure

It consists of membrane-shaped “sacs” called cisterns. The latter have an elongated shape, slightly flattened in the middle and expanded at the edges. The complex also contains round Golgi vesicles - small membrane structures. The cisternae are “folded” into stacks called dictyosomes. The Golgi apparatus contains various types of “sacs”; the entire complex is divided into certain parts according to the degree of distance from the nucleus. There are three of them: the cis section (closer to the nucleus), the middle section, and the trans section - the farthest from the nucleus. They are characterized by a different composition of enzymes, and therefore the work performed. There is one feature in the structure of dictyosomes: they are polar, that is, the section closest to the nucleus only receives vesicles coming from the endoplasmic reticulum. The part of the “stack” facing the cell membrane only forms and releases them.

Golgi apparatus: functions

The main tasks performed are the sorting of proteins, lipids, mucous secretions and their removal. Non-protein substances secreted by the cell and carbohydrate components of the outer membrane also pass through it. At the same time, the Golgi apparatus is not at all an indifferent mediator that simply “transmits” substances; processes of activation and modification (“maturation”) take place in it:

1. Sorting of substances, transport of proteins. The distribution of protein substances occurs into three streams: for the membrane of the cell itself, export, and lysosomal enzymes. In addition to proteins, the first stream also includes fats. An interesting fact is that any export substances are transported inside the bubbles. But proteins intended for the cell membrane are embedded in the membrane of the transport vesicle and move in this way.
2. The release of all products produced in the cell. The Golgi apparatus “packs” all products, both protein and other nature, into secretory vesicles. All substances are released through the complex interaction of the latter with the cell membrane.
3. Synthesis of polysaccharides (glycosaminoglycans and components of the cell wall glycocalyx).
4. Sulfation, glycosylation of fats and proteins, partial proteolysis of the latter (necessary to convert them from an inactive form to an active one) - these are all processes of “maturation” of proteins necessary for their future full-fledged work.

Finally

Having examined how the Golgi complex is structured and works, we are convinced that it is the most important and integral part of any cell (especially secretory cells). A cell that does not produce substances for export also cannot do without this organelle, since the “completion” of the cell membrane and other important internal processes of life depend on it.

Golgi complex It is a stack of membrane sacs (cisterns) and an associated system of bubbles.

On the outer, concave side there is a stack of bubbles budding from the smooth. EPS, new tanks are constantly forming, 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 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 discovered in 1898 by C. Golgi. Having extremely primitive equipment and a limited set of reagents, he made a discovery that, together with Ramon y Cajal, received the Nobel Prize. He treated the nerve cells with a dichromate solution, after which he added silver and osmium nitrates. By precipitating osmium or silver salts with cellular structures, Golgi discovered a dark-colored network in neurons, which he called the internal reticular apparatus. When stained using general methods, the lamellar complex does not accumulate dyes, so the zone of its concentration is visible as a light area. For example, near the nucleus of a plasma cell, a light zone is visible, corresponding to the area where the organelle is located.

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

The Golgi complex is the site of condensation and accumulation of secretion products produced in other parts of the cell, mainly in the ER. During protein synthesis, radiolabeled amino acids accumulate in gr. ER, 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 closely 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 at the periphery expansions are formed - ampoules, the width of which is not constant. Each stack contains about 5...10 tanks. In addition to densely located flat cisterns, in the area of ​​the Golgi complex there are a large number of small vesicles (vesicles), especially at the edges of the organelle. Sometimes they become detached from the ampoules.

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

The Golgi complex is polarized, that is, qualitatively heterogeneous from different sides. It has an immature cis surface, lying closer to the nucleus, and a mature trans surface, facing the cell surface. Accordingly, the organelle consists of several interconnected compartments that perform specific functions.

The cis compartment usually faces the cell center. Its outer surface has a convex shape. Microvesicles (transport pinocytosis vesicles) coming from the EPS merge with the cisterns. Membranes are constantly renewed due to vesicles and, in turn, replenish the contents of membrane formations in other compartments. Post-translational processing of proteins begins in the compartment and continues in subsequent parts of the complex.

The intermediate compartment carries out glycosylation, phosphorylation, carboxylation, and sulfation of biopolymer protein complexes. The so-called post-translational modification of polypeptide chains occurs. Synthesis of glycolipids and lipoproteins is underway. 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, the 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. The trans-compartment partially transforms into the trans-network - a system of vesicles, vacuoles and tubules.

In cells, individual dictyosomes can be linked to each other by a system of vesicles and cisternae adjacent to the distal end of a cluster 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, the sorting of proteins and other substances, the formation of secretory granules, precursors of primary lysosomes and spontaneous secretion vesicles occur. Secretory vesicles and prelysosomes are surrounded by proteins called clathrins.

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

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

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

In the cisterns of the Golgi complex, secondary changes occur in proteins synthesized in the group. EPS. These changes are associated with the rearrangement of oligosaccharide chains of glycoproteins. Inside the cavities of the Golgi complex, lysosomal proteins and secretion proteins are modified with the help of transglucosidases: oligosaccharide chains are successively replaced and extended. Modifying proteins move from the cis-compartment cisternae to the trans-compartment cisternae due to transport in vesicles containing the protein.

In the trans-compartment, proteins are sorted: on the inner surfaces of the cisternae membranes there are protein receptors that recognize secretory proteins, membrane proteins and lysosomes (hydrolases). As a result, three types of small vacuoles are split off from the distal trans-sections of dictyosomes: prelysosomes containing hydrolases; with secretory inclusions, vacuoles that replenish the cell membrane.

The secretory function of the Golgi complex is that the exported protein synthesized on ribosomes, separated and accumulated inside the ER cisterns, is transported to the vacuoles of the lamellar apparatus. The accumulated protein can then condense to form secretory protein granules (in the pancreas, mammary and other glands) or remain dissolved (immunoglobulins in plasma cells). Vesicles containing these proteins are split off from the ampullary extensions of the cisterns of the Golgi complex. Such vesicles can merge with each other and increase in size, forming secretory granules.

After this, the secretory granules begin to move to the cell surface, come into contact with the plasmalemma, with which their own membranes merge, and the contents of the granules appear outside the cell. Morphologically, this process is called extrusion, or excretion (throwing out, 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 secretory function, which is usually accompanied by the development of the ER, and in the case of protein synthesis, the nucleolus.

During cell division, the Golgi complex breaks down into individual cisterns (dictyosomes) and/or vesicles, which are distributed between the two dividing cells and, at the end of telophase, restore the structural integrity of the organelle. Outside of division, the membrane apparatus is continuously renewed due to vesicles migrating from the EPS and distal cisternae of the dictyosome at the expense of the proximal compartments.

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