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

Structure

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

Functions

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

Lecture 3. Vacuolar system

Lecture plan

1. Classification of the components of the vacuolar system
2. Endoplasmic reticulum. History of its study, morphology and functions.
3. Golgi complex. History of study. Morphology and functions.
4. Lysosomes. Story. intracellular digestion.
5. Nuclear shell system. Morphology and functions.
6. Description of the scheme of interconversions of the components of the vacuolar system.

Definition of the vacuolar system

The vacuolar system is a system of organelles consisting of membrane vesicles different shapes, connected in a certain way with each other and the plasma membrane.

One of the essential properties of the vacuolar system is the division of the cell into compartments (compartments) - hyaloplasm and contents inside the membrane compartments.

The composition of the vascular system includes the following components: sEPS, GLEPS, KG, lysosomes, and SNAO.

Endoplasmic reticulum (EPR)

The endoplasmic reticulum consists of two varieties - smooth and rough, which differ in the absence or presence of ribosomes on the surface of the membranes. This organelle belongs to the organelles general purpose and is part of the cytoplasm of all types of eukaryotic cells.

Rough XPS

This organoid was discovered in 1943 by Claude by differential centrifugation. When separating the cell homogenate into fractions in centrifuge tubes, 3 main fractions can be identified: supernatant, microsomal and nuclear fractions.

It is the composition of the microsomal fraction, which contains many vacuoles with a variety of contents, that includes the components of the vacuolar system.

Scheme of the structure of the EPS of a hepatocyte (Fig. Punina M.Yu.)

1 - rough EPS; 2 - smooth EPS; 3 - mitochondrion

In 1945, Porter, when studying whole cells of chicken fibroblasts in an electron microscope, found small and large vacuoles and tubules connecting them in the endoplasmic zone. It was this component of the cell that was called the endoplasmic reticulum.

Using the methods of transmission electron microscopy, it was found that EPS consists of:

· from a system of flat membrane bags (cistern) connected by jumpers (anastomoses).

Rice. Endoplasmic reticulum

1 - tubules of smooth EPS; 2 - tanks of granular (rough) EPS; 3 - outer nuclear membrane covered with ribosomes; 4 – pore complex; 5 - inner nuclear membrane (according to Kristich with changes).

These membranous sacs, as seen in electron microscope photographs, are concentrated in concentric layers around the nucleus. The size of the inner compartment is about 20 nm to 1 micron (1,000 nm). The number of wEPS elements in cells depends on their function and degree of differentiation. The concentration of sEPS cisterns in cells in the area around the nucleus is called ergastoplasm and indicates the participation of such cells in the synthesis of export protein.

Ribosomes attached to the surface of sERM membranes can be single or in the form of rosettes (polysomes). The depth of penetration of ribosomes into membranes can also differ.

The mechanism of functioning of the rough.EPS

1. Function of export protein synthesis. Hypothesis of Blobel and Sabatini (1966 - 1970).

This function is carried out with the participation of the sER membranes themselves and the membrane layer of the hyaloplasm, in which the system responsible for all stages of translation is concentrated.

It is assumed that there are special sites on the surface of sERM membranes responsible for the recognition of terminal fragments of mRNA molecules. The attachment of these molecules precedes the start of the actual translation process. During translation, synthesized export proteins first pass through a channel in the large subunit of the ribosome and then across the membrane. Inside the membrane compartment, these proteins accumulate. Their further fate is connected with the processes of maturation.

2. Segregation and transformation of export proteins.

The essence of ripening processes lies in the fact that the signal sequence is cut off from individual protein molecules with the help of special enzymes, other enzymes attach either radicals or fragments of carbohydrate and lipid molecules to them, in the case of the formation of secrets that are complex in chemical composition.

If these are membrane proteins, then, depending on their position in the bilipid layer (outside, inside or on the surface, protein molecules move from the large subunit of the ribosome to one or another surface of the membrane or penetrate it through (integral proteins).

Scheme of molecular organization of rough EPS and its role in the processes of synthesis and secondary transformations of protein molecules (Fig. Punina M.Yu.)

1 - membrane; 2 - semi-integral proteins and glycoproteins; 3 - oligosaccharides and other carbohydrate components on the inner surface of the membranes and in the cavity of the tanks; 4 - mRNA; 5 - hypothetical receptor in the membrane for mRNA; 6, 7 - subunits of ribosomes; (6 - small, 7 - large); 8 - unidentified integral membrane proteins that ensure the passage of the synthesized proteins through the membrane; 9 - hypothetical integral proteins that provide attachment to the membrane of large subunits of ribosomes; 10 - synthesized protein molecule; 11 - 13 - variants of the synthesis of integral (13), semi-integral proteins of the outer (11) and inner (12) layers of the membrane; 14 - synthesis of hyaloplasmic proteins on the attached ribosome; 15 - 17 - successive stages of synthesis, passage through the membrane and secondary changes in export proteins.

In the upper left corner - appearance rough EPS in an electron microscope; in the right corner, typical relationships between the polysome and the rough ER membrane during the synthesis of export and semi-integral proteins; in the center - the cytoplasmic pool of ribosome subunits.

Arrows show the direction of movement of ribosome subunits and synthesized protein molecules.

3. Intramembrane storage of substances.

Some secrets are stored in the intramembrane space for a certain time, after which they are packed into small membrane vesicles, which transfer the secret from sEPS to the Golgi complex formation zone. Thus, when studying the formation of protein molecules of antibodies, it was found that the molecule itself is built in 90 seconds, but it appears outside the cell only after 45 minutes. That is, during secretion, the following stages are established: protein synthesis, segregation (separation), intracellular transport, concentration, intracellular storage, release from the cell.

4. Participation in the renewal of membrane components (place of formation of a new membrane). Hypothesis of Lodish and Rothman (1977).

The inner part of the bilipid layer of the membrane cisterns of sEPS is the site of incorporation of newly synthesized lipid molecules. After the growth of the surface of the inner part of the bilipid layer, the excess of lipid molecules jumps to the outer layer of the bilipid surface due to the vertical mobility of lipid molecules (the flip-flop property).

Smooth endoplasmic reticulum

Unlike SHEPS, this type of network has two significant differences:

Membrane bubbles have the form of a complex system of tubules;

The surface of the membrane is smooth, devoid of ribosomes.

The arrangement of the tubules of the smooth EPS (sarcoplasmic reticulum) muscles.

M - mitochondria. (after Fawcett & McNutt, 1969)

This organoid also belongs to general purpose organelles, but in some cells it makes up the bulk of the cytoplasm of such cells. This is due to the fact that these cells are involved in the formation of non-membrane lipids. An example of such cells are the cells of the adrenal cortex, which specialize in the production of steroid hormones. In the cytoplasm of these cells, a continuous mass of tubules of smooth ER is observed. Smooth ER usually occupies a strictly defined place in the cell: in the intestinal cells - in the apical zone, in the liver cells in the zone of glycogen deposition, in the interstitial cells of the testis, it is evenly distributed throughout the cytoplasm.

The origin of smooth EPS is secondary. This organoid is formed from sER as a result of the loss of the last ribosomes, or due to the growth of sER in the form of tubules devoid of ribosomes.

Functioning mechanism of smooth EPS

1. Participation in the synthesis of non-membrane lipids.

This function is associated with the secretion of these substances, such as steroid hormones.

2. Detoxification (intra-membrane storage of toxic waste products of metabolism).

This function is associated with the ability of the tubules of smooth EPS of liver cells to accumulate toxic metabolic products, such as certain drugs, in the intra-membrane space (a phenomenon known for barbiturates).

3. Accumulation of divalent cations.

This function is characteristic of the L-channels of muscle fibers. Inside these channels, divalent Ca +2 ions accumulate, which are involved in the formation of calcium bridges between actin and myosin molecules during muscle contraction.

The structure of the endoplasmic reticulum

Definition 1

Endoplasmic reticulum(EPS, endoplasmic reticulum) is a complex ultramicroscopic, highly branched, interconnected system of membranes that more or less evenly permeates the mass of the cytoplasm of all eukaryotic cells.

EPS is a membrane organelle consisting of flat membrane sacs - cisterns, channels and tubules. Due to this structure, the endoplasmic reticulum significantly increases the area of ​​\u200b\u200bthe inner surface of the cell and divides the cell into sections. It's filled inside matrix(moderately dense loose material (synthesis product)). The content of various chemicals in the sections is not the same, therefore, in the cell, both simultaneously and in a certain sequence, various chemical reactions can occur in a small volume of the cell. The endoplasmic reticulum opens into perinuclear space(a cavity between two membranes of a karyolem).

The membrane of the endoplasmic reticulum consists of proteins and lipids (mainly phospholipids), as well as enzymes: adenosine triphosphatase and enzymes for the synthesis of membrane lipids.

There are two types of endoplasmic reticulum:

• Smooth (agranular, AES), represented by tubules that anastomose with each other and do not have ribosomes on the surface;
• Rough (granular, grES), also consisting of interconnected tanks, but they are covered with ribosomes.

Remark 1

Sometimes they allocate more passing or transient(tES) endoplasmic reticulum, which is located in the area of ​​transition of one type of ES to another.

Granular ES is characteristic of all cells (except spermatozoa), but the degree of its development is different and depends on the specialization of the cell.

GRES of epithelial glandular cells (pancreas producing digestive enzymes, liver - synthesizing serum albumins), fibroblasts (cells connective tissue producing collagen protein), plasma cells (producing immunoglobulins).

Agranular ES predominates in the cells of the adrenal glands (synthesis of steroid hormones), in muscle cells (calcium metabolism), in the cells of the fundic glands of the stomach (release of chloride ions).

Another type of EPS membranes are branched membrane tubules containing inside a large number of specific enzymes, and vesicles - small, membrane-bound vesicles, mostly located near tubules and cisterns. They provide the transfer of those substances that are synthesized.

EPS functions

The endoplasmic reticulum is an apparatus for the synthesis and, in part, the transport of cytoplasmic substances, thanks to which the cell performs complex functions.

Remark 2

The functions of both types of EPS are associated with the synthesis and transport of substances. The endoplasmic reticulum is a universal transport system.

Smooth and rough endoplasmic reticulum with their membranes and contents (matrix) perform common functions:

• dividing (structuring), due to which the cytoplasm is orderly distributed and does not mix, and also prevents random substances from entering the organelle;
• transmembrane transport, due to which the necessary substances are transferred through the membrane wall;
• synthesis of membrane lipids with the participation of enzymes contained in the membrane itself and ensuring the reproduction of the endoplasmic reticulum;
• due to the potential difference that occurs between the two surfaces of the ES membranes, it is possible to ensure the conduction of excitation pulses.

In addition, each type of network has its own specific functions.

Functions of the smooth (agranular) endoplasmic reticulum

The agranular endoplasmic reticulum, in addition to the named functions common to both types of ES, also performs functions peculiar only to it:

• calcium depot. In many cells (skeletal muscle, heart, eggs, neurons) there are mechanisms that can change the concentration of calcium ions. striated muscle contains a specialized endoplasmic reticulum called the sarcoplasmic reticulum. This is a reservoir of calcium ions, and the membranes of this network contain powerful calcium pumps capable of ejecting a large amount of calcium into the cytoplasm or transporting it into the cavities of the network channels in hundredths of a second;
• lipid synthesis, substances such as cholesterol and steroid hormones. Steroid hormones are synthesized mainly in the endocrine cells of the gonads and adrenal glands, in the cells of the kidneys and liver. Intestinal cells synthesize lipids, which are excreted into the lymph, and then into the blood;

detoxification function– neutralization of exogenous and endogenous toxins;

Example 1

Kidney cells (hepatocytes) contain oxidase enzymes that can destroy phenobarbital.

organelle enzymes are involved in glycogen synthesis(in liver cells).

Functions of the rough (granular) endoplasmic reticulum

For the granular endoplasmic reticulum, in addition to the listed general functions, special ones are also characteristic:

• protein synthesis at the TPP has some peculiarities. It begins on free polysomes, which subsequently bind to ES membranes.
• The granular endoplasmic reticulum synthesizes: all proteins of the cell membrane (except for some hydrophobic proteins, proteins of the inner membranes of mitochondria and chloroplasts), specific proteins of the internal phase of membrane organelles, as well as secretory proteins that are transported through the cell and enter the extracellular space.
• post-translational modification of proteins: hydroxylation, sulfation, phosphorylation. An important process is glycosylation, which occurs under the action of the membrane-bound enzyme glycosyltransferase. Glycosylation occurs before the secretion or transport of substances to certain parts of the cell (Golgi complex, lysosomes or plasmalemma).
• transport of substances along the intramembrane part of the network. Synthesized proteins move along the intervals of ES to the Golgi complex, which removes substances from the cell.
• due to the involvement of the granular endoplasmic reticulum the Golgi complex is formed.

The functions of the granular endoplasmic reticulum are associated with the transport of proteins that are synthesized in ribosomes and located on its surface. Synthesized proteins enter the ER, twist and acquire a tertiary structure.

The protein that is transported to the tanks changes significantly along the way. It can, for example, be phosphorylated or converted to a glycoprotein. The usual route for a protein is through the granular ER to the Golgi apparatus, from where it either exits the cell, or enters other organelles of the same cell, such as lysosomes), or is deposited as storage granules.

In liver cells, both granular and non-granular endoplasmic reticulum take part in the processes of detoxification of toxic substances, which are then removed from the cell.

Like the outer plasma membrane, the endoplasmic reticulum has selective permeability, as a result of which the concentration of substances inside and outside the reticulum channels is not the same. It matters for the function of the cell.

Example 2

There are more calcium ions in the endoplasmic reticulum of muscle cells than in its cytoplasm. Leaving the channels of the endoplasmic reticulum, calcium ions start the process of contraction of muscle fibers.

Formation of the endoplasmic reticulum

The lipid components of the membranes of the endoplasmic reticulum are synthesized by the enzymes of the network itself, the protein comes from the ribosomes located on its membranes. The smooth (agranular) endoplasmic reticulum does not have its own protein synthesis factors, therefore it is believed that this organelle is formed as a result of the loss of ribosomes by the granular endoplasmic reticulum.

5. Light microscope, its main characteristics. Phase contrast, interference and ultraviolet microscopy.

6. Resolution of the microscope. Possibilities of light microscopy. The study of fixed cells.

7. Methods of autoradiography, cell cultures, differential centrifugation.

8. The method of electron microscopy, the variety of its possibilities. Plasma membrane, structural features and functions.

9. Surface apparatus of the cell.

11. Plant cell wall. Structure and functions - cell membranes of plants, animals and prokaryotes, comparison.

13. Organelles of the cytoplasm. Membrane organelles, their general characteristics and classification.

14. Eps granular and smooth. The structure and features of functioning in cells of the same type.

15. Golgi complex. Structure and functions.

16. Lysosomes, functional diversity, education.

17. Vacular apparatus of plant cells, components and features of organization.

18. Mitochondria. The structure and functions of the mitochondria of the cell.

19. Functions of cell mitochondria. ATP and its role in the cell.

20. Chloroplasts, ultrastructure, functions in connection with the process of photosynthesis.

21. Variety of plastids, possible ways of their interconversion.

23. Cytoskeleton. Structure, functions, features of organization in connection with the cell cycle.

24. The role of the method of immunocytochemistry in the study of the cytoskeleton. Features of the organization of the cytoskeleton in muscle cells.

25. Nucleus in plant and animal cells, structure, functions, relationship between the nucleus and cytoplasm.

26. Spatial organization of intraphase chromosomes inside the nucleus, euchromatin, heterochromatin.

27. Chemical composition of chromosomes: DNA and proteins.

28. Unique and repetitive DNA sequences.

29. Proteins of chromosomes histones, non-histone proteins; their role in chromatin and chromosomes.

30. Types of RNA, their functions and formation in connection with the activity of chromatin. The central dogma of cell biology: dna-rna-protein. The role of components in its implementation.

32. Mitotic chromosomes. Morphological organization and functions. Karyotype (on the example of a person).

33. Reproduction of chromosomes of pro- and eukaryotes, relationship with the cell cycle.

34. Polytene and lampbrush chromosomes. Structure, functions, difference from metaphase chromosomes.

36. Nucleolus

37. Nuclear membrane structure, functions, role of the nucleus in interaction with the cytoplasm.

38. Cell cycle, periods and phases

39. Mitosis as the main type of division. Open and closed mitosis.

39. Stages of mitosis.

40. Mitosis, common features and differences. Features of mitosis in plants and animals:

41. Meiosis meaning, characteristics of phases, difference from mitosis.

14. Eps granular and smooth. The structure and features of functioning in cells of the same type.

Endoplasmic reticulum (EPS) - a system of communicating or separate tubular channels and flattened cisterns located throughout the cytoplasm of the cell. They are delimited by membranes (membrane organelles). Sometimes tanks have expansions in the form of bubbles. EPS channels can connect with surface or nuclear membranes, contact with the Golgi complex.

In this system, smooth and rough (granular) EPS can be distinguished.

Rough EPS. On the channels of the rough ER, ribosomes are located in the form of polysomes. Here, the synthesis of proteins occurs, mainly produced by the cell for export (removal from the cell), for example, secretions of glandular cells. Here, the formation of lipids and proteins of the cytoplasmic membrane and their assembly take place. The densely packed cisterns and channels of the granular ER form a layered structure where protein synthesis proceeds most actively. This place is called ergastoplasm.

Smooth EPS. There are no ribosomes on smooth ER membranes. Here, mainly the synthesis of fats and similar substances (for example, steroid hormones), as well as carbohydrates, proceeds. The channels of the smooth ER also move finished material to the place of its packing into granules (to the zone of the Golgi complex). In hepatic cells, smooth ER takes part in the destruction and neutralization of a number of toxic and medicinal substances (for example, barbiturates). In the striated muscles, the tubules and cisterns of the smooth ER deposit calcium ions.

15. Golgi complex. Structure and functions.

The Golgi complex is a membrane structure inherent in any eukaryotic cell. The Golgi complex consists of flattened cisterns, usually arranged in stacks (dictyosomes). The tanks are not isolated, but are interconnected by a system of tubes. The first cistern from the nucleus is called the cis-pole of the Golgi complex, and the last, respectively, the trans-pole. The number of cisterns in different cells of different organisms may vary, but in general the structure of the Golgi complex is approximately the same in all eukaryotes. In secretory cells, it is especially strongly developed. The functions of the Golgi complex are to transport proteins to their destination, as well as their glycosylation, deglycosylation, and modification of oligosaccharide chains.

The Golgi complex is characterized by functional anisotropy. Newly synthesized proteins are transported from the endoplasmic reticulum to the cis-pole of dictyosomes using vesicles. Then they gradually move towards the trans-pole, undergoing gradual modifications (as they move away from the nucleus, the composition of the enzyme systems in the tanks changes). Finally, the proteins travel to their final destination in vesicles budding from the trans pole. The Golgi complex ensures the transport of proteins into three compartments: to lysosomes (as well as to the central vacuole of the plant cell and contractile vacuoles of protozoa), to the cell membrane, and to the intercellular space. The direction of protein transfer is determined by special glycosidic labels. For example, a marker for lysosomal enzymes is mannose-6-phosphate. The maturation and transport of mitochondrial, nuclear and chloroplast proteins occurs without the participation of the Golgi complex: they are synthesized by free ribosomes and then enter directly into the cytosol. An important function of the Golgi complex is the synthesis and modification of the carbohydrate component of glycoproteins, proteoglycans and glycolipids. It also synthesizes many polysaccharides, such as hemicellulose and pectin in plants. The cisternae of the Golgi complex contain a whole range of different glycosyltransferases and glycosidases. They also undergo sulfation of carbohydrate residues.

Animals and man. The functions of this component part of the cell are diverse and are mainly associated with the synthesis, modification and transport

The endoplasmic reticulum was first discovered in 1945. The American scientist K. Porter saw it with the help of one of the first electric microscopes. Since that time, active research has begun.

There are two types of this organelle in the cell:

• Granular, or rough endoplasmic reticulum (covered with many ribosomes).
• Agranular or smooth endoplasmic reticulum.

Each type of reticulum has some features and performs completely different functions. Let's look at them in more detail.

Granular endoplasmic reticulum: structure. This organelle is a system of tanks, vesicles and tubules. Its walls are composed of bilipid membrane. The width of the cavity can vary from 20 nm to several micrometers - everything here depends on the secretory activity of the cell.

Few specialized cells that are characterized low level metabolism, EPS is represented by only a few disparate cisterns. Inside a cell that actively synthesizes protein, the endoplasmic reticulum consists of many cisterns and an extensive system of tubules.

As a rule, granular ER is associated with the membranes of the nuclear membrane through tubules - this is how complex processes of synthesis and transport of protein molecules occur.

Granular endoplasmic reticulum: functions. As already mentioned, the entire surface of the EPS from the side of the cytoplasm is covered with ribosomes, which, as is known, are involved in EPS - this is the site of the synthesis and transport of protein compounds.

This organelle is responsible for the synthesis of the cytoplasmic membrane. But in most cases, the created protein molecules are further transported with the help of membrane vesicles to where they are further modified and distributed according to the needs of the cell and tissues.

In addition, some changes in the protein occur in the cavities of the EPS tanks, for example, the addition of a carbohydrate component to it. Here, by aggregation, large secretory granules are formed.

Agranular endoplasmic reticulum: structure and functions. The structure of smooth EPS has some differences. For example, such an organelle consists only of cisterns and does not have a system of tubules. Complexes of such EPS, as a rule, are smaller, but the width of the tank, on the contrary, is larger.

The smooth endoplasmic reticulum is not related to the synthesis of protein components, but performs a number of equally important functions. For example, it is here that steroid hormones are synthesized in humans and all vertebrates. That is why the volume of smooth ER in the cells of the adrenal glands is quite large.

In liver cells, EPS produces the necessary enzymes that are involved in carbohydrate metabolism, namely, in the breakdown of glycogen. It is also known that liver cells are responsible for the disposal of toxins. In the cisterns of this organelle, a hydrophilic component is synthesized, which then attaches to the toxic molecule, increasing its solubility in the blood and urine. Interestingly, in hepatocytes, which are constantly exposed to toxins (poisons, alcohol), almost the entire cell is occupied by densely located cisterns of smooth ER.

In muscle cells, there is a special kind of smooth EPS - the sarcoplasmic reticulum. It acts as a depot of calcium, thus regulating the processes of cell activity and rest.

As can be seen, the functions of the EPS are diverse and very important for the normal functioning of a healthy cell.