Rough eps. The structure and functions of EPS

A bit of history

The cell is considered the smallest structural unit of any organism, however, it also consists of something. One of its components is the endoplasmic reticulum. Moreover, EPS is a mandatory component of any cell in principle (except for some viruses and bacteria). It was discovered by the American scientist K. Porter back in 1945. It was he who noticed the systems of tubules and vacuoles, which, as it were, accumulated around the nucleus. Porter also noted that the sizes of EPS in the cells of different creatures and even organs and tissues of the same organism are not similar to each other. He came to the conclusion that this is due to the functions of a particular cell, the degree of its development, as well as the stage of differentiation. For example, in humans, EPS is very well developed in the cells of the intestines, mucous membranes and adrenal glands.

concept

EPS is a system of tubules, tubules, vesicles and membranes that are located in the cytoplasm of the cell.

Endoplasmic reticulum: structure and functions

Structure
	First, it is a transport function. Like the cytoplasm, the endoplasmic reticulum provides for the exchange of substances between organelles. Secondly, ER performs structuring and grouping of the contents of the cell, breaking it into certain sections. Thirdly, the most important function is protein synthesis, which is carried out in the ribosomes of the rough endoplasmic reticulum, as well as the synthesis of carbohydrates and lipids, which occurs on the membranes of smooth EPS.
EPS structure In total, there are 2 types of endoplasmic reticulum: granular (rough) and smooth. The functions performed by this component depend on the type of the cell itself. On the membranes of the smooth network there are departments that produce enzymes, which are then involved in metabolism. The rough endoplasmic reticulum contains ribosomes on its membranes.

Brief information about the other most important components of the cell

Cytoplasm: structure and functions

Image	Structure	Functions
	It is the fluid in the cell. It is in it that all organelles are located (including the Golgi apparatus, and the endoplasmic reticulum, and many others) and the nucleus with its contents. Refers to the mandatory components and is not an organoid as such.	The main function is transport. It is thanks to the cytoplasm that all organelles interact, their ordering (fold into single system) and the course of all chemical processes.

Cell membrane: structure and functions

Image	Structure	Functions
	Molecules of phospholipids and proteins, forming two layers, make up the membrane. It is the thinnest film that envelops the entire cell. Its integral component is also polysaccharides. And in plants outside, it is still covered with a thin layer of fiber.	The main function of the cell membrane is to limit the internal contents of the cell (cytoplasm and all organelles). Since it contains the smallest pores, it provides transport and metabolism. It can also be a catalyst in the implementation of some chemical processes and a receptor in the event of an external danger.

Core: structure and functions

Image	Structure	Functions
	It is either oval or spherical in shape. It contains special DNA molecules, which in turn carry the hereditary information of the whole organism. The core itself is covered on the outside with a special shell in which there are pores. It also contains nucleoli (small bodies) and liquid (juice). Around this center is the endoplasmic reticulum.	It is the nucleus that regulates absolutely all processes occurring in the cell (metabolism, synthesis, etc.). And it is this component that is the main carrier of hereditary information of the whole organism. The nucleolus is where protein and RNA are synthesized.

Ribosomes

They are organelles that provide basic protein synthesis. They can be located both in the free space of the cytoplasm of the cell, and in combination with other organelles (endoplasmic reticulum, for example). If the ribosomes are located on the membranes of the rough EPS (being on the outer walls of the membranes, the ribosomes create roughness) , the efficiency of protein synthesis increases several times. This has been proven by numerous scientific experiments.

Golgi complex

An organelle consisting of several cavities that constantly secrete various sizes bubbles. The accumulated substances are also used for the needs of the cell and the body. The Golgi complex and the endoplasmic reticulum are often located side by side.

Lysosomes

Organelles surrounded by a special membrane and performing the digestive function of the cell are called lysosomes.

Mitochondria

Organelles surrounded by several membranes and performing an energy function, that is, providing the synthesis of ATP molecules and distributing the energy received throughout the cell.

Plastids. Types of plastids

Chloroplasts (function of photosynthesis);

Chromoplasts (accumulation and preservation of carotenoids);

Leukoplasts (accumulation and storage of starch).

Organelles designed for locomotion

They also make some movements (flagella, cilia, long processes, etc.).

Cell center: structure and functions

The endoplasmic reticulum or EPS is a collection of membranes relatively evenly distributed throughout the cytoplasm of eukaryotic cells. EPS has a huge number of branches and is a complex structured system of relationships.

EPS is one of the components cell membrane. It itself includes channels, tubules and tanks, allowing you to distribute the internal space of the cell to certain areas, as well as significantly expand it. The entire place inside the cell is filled with a matrix - a dense synthesized substance, and each of its sections has a different chemical composition. Therefore, several chemical reactions can take place in the cell cavity at once, covering only a certain area, and not the entire system. Ends EPS perinuclear space.

Lipids and proteins are the main substances in the membrane of the endoplasmic reticulum. Often there are also various enzymes.

Types of EPS:

• Agranular (aPS) - in essence - a system of fastened tubules that does not contain ribosomes. The surface of such EPS, due to the absence of anything on it, is smooth.
• Granular (grES) - the same as the previous one, but it has ribosomes on the surface, due to which roughness is observed.

In some cases, this list includes the transient endoplasmic reticulum (tER). Its second name is passing. It is located at the junction of two types of networks.

Rough ES can be observed inside all living cells, excluding spermatozoa. However, in each organism it is developed to varying degrees.

For example, HRES is quite highly developed in plasma cells that produce immunoglobulins, in collagen-producing fibroblasts, and in glandular epithelial cells. The latter are found in the pancreas, where enzymes are synthesized, and in the liver, producing albumins.

Smooth ES is represented by cells of the adrenal glands, which are known to create hormones. It can also be found in the muscles, where calcium is exchanged, and in the fundic gastric glands, which secrete chlorine.

There are also two types of internal EPS membranes. The first is a system of tubules with numerous branches, they are saturated with a variety of enzymes. The second type - vesicles - small vesicles with their own membrane. They perform a transport function for synthesized substances.

EPS functions

First of all, the endoplasmic reticulum is a synthesizing system. But it is also no less involved in the transport of cytoplasmic compounds, which makes the entire cell capable of more complex functional features.

The above features of EPS are typical for any of its types. Thus, this organelle is a universal system.

General functions for granular and agranular network:

• Synthesizing - the production of membrane fats (lipids) with the help of enzymes. They allow EPS to reproduce independently.
• Structuring - organizing areas of the cytoplasm and preventing unwanted substances from entering it.
• Conductive - the occurrence of exciting impulses due to the reaction between the membranes.
• Transport - removal of substances even through the membrane walls.

In addition to the main features, each kind of endoplasmic reticulum has its own specific functions.

Functions of the smooth (agranular) endoplasmic reticulum

NPP, in addition to the features inherent in all types of EPS, has its own following functions:

• Detoksikatsionnaya - the elimination of toxins both inside and outside the cell.

Phenobarbital is destroyed in the cells of the kidneys, namely, in hepatocytes, due to the action of oxidase enzymes.

• Synthesizing - the production of hormones and cholesterol. The latter is excreted in several places at once: the gonads, kidneys, liver and adrenal glands. And in the intestines, fats (lipids) are synthesized, which enter the blood through the lymph.

AES promotes the synthesis of glycogen in the liver, due to the action of enzymes.

• Transport - sarcoplasmic reticulum, it is also a special EPS in striated muscles, serves as a storage place for calcium ions. And thanks to specialized calcium pumps, it throws calcium directly into the cytoplasm, from where it instantly sends it to the channel area. The muscle ER is engaged in this, due to a change in the amount of calcium by special mechanisms. They are found mainly in the cells of the heart, skeletal muscle, as well as in neurons and the egg.

Functions of the rough (granular) endoplasmic reticulum

As well as agranular, the power plant has functions peculiar only to itself:

• Transport - the movement of substances along the intramembrane section, for example, the produced proteins on the surface of the EPS pass into the Golgi complex, and then exit the cell.
• Synthesizing - everything is the same as before: the production of proteins. But it begins on free polysomes, and only after that the substances bind to the EPS.
• Thanks to the granular endoplasmic reticulum, literally all types of proteins are synthesized: secretory proteins that go inside the cell itself, specific in the internal phase of organelles, as well as all substances in the cell membrane, with the exception of mitochondria, chloroplasts and some types of proteins.
• The generatrix - the Golgi complex is being created, among other things, thanks to the hydroelectric power station.
• Modification - includes phosphorylation, sulfation and hydroxylation of proteins. A special enzyme glycosyltransferase ensures the process of glycosylation. Basically, it precedes the transport of substances to the exit from the cytoplasm or occurs before cell secretion.

It can be seen that the functions of GRES are mainly aimed at regulating the transport of proteins synthesized on the surface of the endoplasmic reticulum in ribosomes. They are converted into a tertiary structure, twisting, namely in the EPS.

The typical behavior of a protein is to enter the granular endoplasmic reticulum, then to the Golgi apparatus and, finally, to exit to other organelles. He can also be postponed as a spare. But often, in the process of moving, he is able to radically change the composition and appearance: phosphorylated, for example, or converted to a glycoprotein.

Both types of the endoplasmic reticulum contribute to the detoxification of liver cells, that is, the removal of toxic compounds from it.

EPS does not allow substances to pass through itself in all areas, due to which the number of connections in the tubules and outside them is different. The permeability of the outer membrane works on the same principle. This feature plays a certain role in the life of the cell.

In the cell cytoplasm of muscles, there are much fewer calcium ions than in its endoplasmic reticulum. The consequence of this is a successful muscle contraction, because it is calcium that provides this process when leaving the EPS channels.

Formation of the endoplasmic reticulum

The main components of EPS are proteins and lipids. The former are transported from membrane ribosomes, the latter are synthesized by the endoplasmic reticulum itself with the help of its enzymes. Since smooth ER (aPS) does not have ribosomes on the surface, and is not capable of synthesizing protein itself, it is formed when ribosomes are discarded by a granular-type network.

In the region of the nexus (0.5–3 μm long), the plasma membranes approach each other at a distance of 2 nm and are pierced by numerous protein channels (connectons) that bind the contents of neighboring cells. Ions and small molecules can diffuse through these channels (2 nm in diameter). characteristic of muscle tissue.

synapses- these are areas of signal transmission from one excitable cell to another. In a synapse, a presynaptic membrane (belonging to one cell), a synaptic cleft, and a postsynaptic membrane (PoM) (part of the plasmalemma of another cell) are distinguished. Typically, the signal is transmitted by a chemical substance - a mediator that acts on specific receptors in the PoM. characteristic of nervous tissue.

Membrane organelles:

Endoplasmic reticulum (ER)- Porter discovered for the first time in the endoplasm of fibroblast, it is divided into two types - granular and agranular(or smooth).

Granular EPS It is a collection of flat sacs (cistern), vacuoles and tubules, from the side of the hyaloplasm the membrane network is covered with ribosomes. In this regard, sometimes another term is used - rough reticulum. On the ribosomes of the granular ER, such proteins are synthesized, which are then either excreted from the cell (export proteins),
or are part of certain membrane structures (membrane proper, lysosomes, etc.).

Functions of granular ER:

1) synthesis on ribosomes of peptide chains of exported, membrane, lysosomal, etc. proteins,

2) isolating these proteins from the hyaloplasm inside the membrane cavities and concentrating them here,

3) chemical modification of these proteins, as well as their binding to hydrocarbons or other components

4) their transport (within the EPS and with the help of individual vesicles).

Thus, the presence of a well-developed granular ER in the cell indicates a high intensity of protein synthesis, especially in relation to secretory proteins.

Smooth EPS unlike granular, it lacks ribosomes. Performs features:

1) synthesis of carbohydrates, lipids, steroid hormones (therefore, it is well expressed in cells synthesizing these hormones eg., in the adrenal cortex, gonads);

2) detoxification of toxic substances (well expressed in liver cells, especially after poisoning), deposition of calcium ions in tanks (in skeletal and cardiac muscle tissue, stimulate contraction after release) and the transport of synthesized substances.

Golgi complex ( for the first time this organelle was discovered by Camillo Golgi in 1898 in the form of a network blackened with silver ) - this is an accumulation of 5-10 flat membrane tanks lying on top of each other, from which small bubbles are laced. Each such cluster is called a dictyosome. There can be many dictyosomes in a cell connected to the ER and to each other by cisterns and tubules. By position and function, dictyosomes are divided into 2 parts: the proximal (cis-) part faces the EPS. The opposite part is called distal (trans-). At the same time, vesicles from the granular ER migrate to the proximal part, the proteins processed in the dictyosome gradually move from the proximal part to the distal part, and, finally, secretory vesicles and primary lysosomes bud from the distal part.

Functions of the Golgi complex:

1) segregation(separation) of the corresponding proteins from the hyaloplasm and concentrating them,

2) continuation of the chemical modification of these proteins, eg binding to hydrocarbons.

3) sorting of these proteins into lysosomal, membrane and export,

4) the inclusion of proteins in the composition of the corresponding structures (lysosomes, secretory vesicles, membranes).

Lysosomes(Deduve in 1949) are membrane vesicles containing enzymes for the hydrolysis of biopolymers, they are formed by budding from the cisterns of the Golgi complex. Dimensions - 0.2-0.5 microns. Function of lysosomes- intracellular digestion of macromolecules. Moreover, in lysosomes they are destroyed as separate macromolecules (proteins, polysaccharides, etc.),
and whole structures - organelles, microbial particles, etc.

Distinguish 3 types of lysosomes which are shown in the electron diffraction pattern.

Primary lysosomes- these lysosomes have a homogeneous content.

Obviously, these are newly formed lysosomes with the initial solution of enzymes (about 50 different hydrolytic enzymes). The marker enzyme is acid phosphatase.

Secondary lysosomes are formed either by the fusion of primary lysosomes with pinocytic or phagocytic vacuoles,
or by capturing the cell's own macromolecules and organelles. Therefore, secondary lysosomes are usually larger in size than primary ones,
and their contents are often heterogeneous: for example, dense bodies are found in it. In the presence of such, they speak of phagolysosomes (heterophagosomes) or autophagosomes (if these bodies are fragments of the cell's own organelles). At various injuries cells, the number of autophagosomes usually increases.

Telolisosomes or residual (residual) bodies, appear then

when intralysosomal digestion does not lead to the complete destruction of the captured structures. At the same time, undigested residues (fragments of macromolecules, organelles and other particles) are compacted,
they are often deposited pigment, and the lysosome itself largely loses its hydrolytic activity. In non-dividing cells, the accumulation of telolisosomes becomes an important factor aging. So, with age, telolisosomes accumulate in the cells of the brain, liver and muscle fibers with the so-called. aging pigment - lipofuscin.

Peroxisomes apparently, like lysosomes, they are formed by lacing off membrane vesicles from the cisternae of the Golgi complex. Found in large quantities in liver cells. However, peroxisomes contain a different set of enzymes. Mainly amino acid oxidases. They catalyze the direct interaction of the substrate with oxygen, and the latter is converted into hydrogen peroxide, H 2 O 2- an oxidizing agent dangerous for the cell.

Therefore, peroxisomes contain catalase- an enzyme that breaks down H 2 O 2 to water and oxygen. Sometimes a crystal-like structure (2) is found in peroxisomes - a nucleoid.

Mitochondria - (at the end of the last century, Altman selectively stained them with sour magenta) have two membranes - outer and inner - of which the second forms numerous invaginations ( cristae) into the mitochondrial matrix. Mitochondria differ from other organelles in two more ways. interesting features. They contain own DNA- from 1 to 50 small identical cyclic molecules. In addition, mitochondria contain own ribosomes, which are somewhat smaller than cytoplasmic ribosomes and are visible as small granules. b) This system of autonomous protein synthesis provides the formation of approximately 5% of mitochondrial proteins. Other mitochondrial proteins are encoded by the nucleus and synthesized by cytoplasmic ribosomes.

The main function of mitochondria- completion of oxidative decay nutrients and the formation due to the energy released during this ATP - a temporary energy accumulator in the cell.

2. The most famous are 2 processes. -

a) Krebs cycle - aerobic oxidation of substances, the end products of which are CO2 leaving the cell and NADH, a source of electrons carried by the respiratory chain.

b) Oxidative phosphorylation- the formation of ATP during the transfer of electrons (and protons) to oxygen.

The transfer of electrons is carried out along the chain of intermediate carriers (the so-called respiratory chain), which embedded in the mitochondrial cristae.
The ATP synthesis system (ATP synthetase, which couples the oxidation and phosphorylation of ADP to ATP) is also located here. As a result of the conjugation of these processes, the energy released during the oxidation of substrates is stored in high-energy bonds of ATP and further ensures the performance of numerous cell functions (eg, muscle contraction). In diseases in the mitochondria, oxidation and phosphorylation are uncoupled, as a result, energy is generated in the form of heat.

c) Other processes taking place in mitochondria: urea synthesis,
breakdown of fatty acids and pyruvate to acetyl-CoA.

Variability in the structure of mitochondria. In muscle fibers, where energy requirements are especially high, mitochondria contain
a large number of densely spaced lamellar (laminar) crist. In liver cells, the number of cristae in mitochondria is much less. Finally, in the cells of the adrenal cortex, the cristae have a tubular structure and look like small vesicles on the cut.

Non-membrane organelles include:

Ribosomes - are formed in the nucleolus. In 1953 they were discovered by Palade, in 1974 he was awarded the Nobel Prize. Ribosomes consist of small and large subunits, have dimensions of 25x20x20 nm, include ribosomal RNA and ribosomal proteins. Function- protein synthesis. Ribosomes can either be located on the surface of the membranes of the granular ER, or freely located in the hyaloplasm, forming clusters - polysomes. If the cell is well developed gr. ER, then it synthesizes proteins for export (eg, fibroblast), if the cell has a poorly developed ER and many free ribosomes and polysomes, then this cell is low-diff and synthesizes proteins for internal use. Regions of the cytoplasm rich in ribosomes and gr. EPS give + p-tion on RNA when stained according to Brache (RNA stained pink with pyronin).

Filaments are the fibrillar structures of the cell. There are 3 types of filaments: 1) microfilaments are thin filaments formed by the globular protein actin (5-7 nm in diameter) form a more or less dense network in cells . As can be seen in the picture, the main direction of the bundles of microfilaments (1) is along the long axis of the cell. 2) the second type of filaments is called myosin filaments (diameter 10-25 nm) in muscle cells, they are closely associated with actin filaments, forming a mifibrilla. 3) filaments of the third type are called intermediate, their diameter is 7-10 nm. They are not directly involved in the mechanisms of contraction, but can influence the shape of cells (accumulating in certain places and, forming a support for organelles, often gather in bundles, forming fibrils). Intermediate filaments are tissue-specific. In the epithelium, they are formed by the protein keratin, in the cells connective tissue- vimentin, in smooth muscle cells - desmin, in nerve cells (shown in the picture) they are called neurofilaments and are also formed by a special protein. By the nature of the protein, it is possible to determine from which tissue the tumor has developed (if keratin is found in the tumor, then it has an epithelial nature, if vimetin - connective tissue).

Filament Functions- 1) form a cytoskeleton 2) participate in intracellular movement (movement of mitochondria, ribosomes, vacuoles, retraction of the cytolemma during phagocytosis 3) participate in the amoeboid movement of cells.

Microvilli - derivatives of cell plasmolemma with a length of about 1 μm, a diameter of about 100 nm, they are based on bundles of microfilaments. Functions: 1) increase the surface of cells 2) perform the function of absorption in the intestinal and renal epithelium.

microtubules also form a dense network in the cell. Net
starts from the perinuclear region (from the centriole) and
propagates radially towards the plasmalemma. Including microtubules run along the long axis of cell processes.

The microtubule wall consists of a single layer of globular subunits of the tubulin protein. On a cross section - 13 such subunits form a ring. In a nondividing (interphase) cell, the network created by microtubules plays the role of a cytoskeleton that maintains the shape of the cell, and also play the role of guiding structures in the transport of substances. In this case, the transport of substances does not go through microtubules, but through the peritubular space. In dividing cells, the network of microtubules is rebuilt and forms the so-called. division spindle. It connects the chromatids of chromosomes with centrioles and contributes to the correct divergence of chromatids to the poles of a dividing cell.

Centrioles. In addition to the cytoskeleton, microtubules form centrioles.
The composition of each of them is reflected by the formula: (9 x 3) + 0 . Centrioles are arranged in pairs - at right angles to each other. Such a structure is called a diplosome. Around the diplosomy - the so-called. centrosphere, a zone of lighter cytoplasm, it contains additional microtubules. Together, the diplosome and centrosphere are called the cell center. A non-dividing cell has one pair of centrioles. The formation of new centrioles (when preparing a cell for division) occurs by duplication (doubling): each centriole acts as a matrix, perpendicular to which a new centriole is formed (by polymerization of tubulin). Therefore, as in DNA, in each diplosome one centriole is the parent centriole, and the second is the daughter centriole.

Smooth endoplasmic reticulum.

The endoplasmic reticulum is divided into two types - smooth and rough.

Smooth EPS is also called agranular.

The smooth endoplasmic reticulum arises and develops due to the granular endoplasmic reticulum (when it is released from ribosomes)।

A smooth network consists of tubules, the walls of which are membranes, channels and bubbles of a smaller cross section than in a rough network. The diameter of the vacuoles and tubules of the smooth endoplasmic reticulum is usually about 50-100 nm. Its functions are also diverse: membrane lipids are synthesized here, but, in addition to them, non-membranelipids (for example, special hormones of animals), toxic substances are neutralized by special enzyme complexes, ions accumulate. So, in striated muscles, the smooth network serves as a reservoir of calcium ions. The membranes of this network contain powerful calcium "pumps" that carry a large amount of calcium ions in any direction in hundredths of a second. Carbohydrates are also synthesized. In specialized cells, the appearance of a smooth network is different, which is associated with its specific functions in intracellular metabolism.

The smooth network is characterized by the presence of enzyme systems involved in the keyout links of metabolism. The smooth endoplasmic reticulum is easily damaged during hypoxia, activation of endogenous phospholipases. Loss of its functions in cells reZko reduces the body's resistance to exogenous and endogenous pathogenic products and contributes to the development of the disease.

Smooth EPS is well developed in those cells in which the processes of synthesis and splitting of lipids take place. These are cells of the adrenal glands and testicles (steroid hormones are synthesized in them), liver cells, muscle cells, intestinal epithelial cells.

In the membranes of smooth EPS, hydroxylation enzymes are built in - a special oxidation method, sometimes called microsomal, is used in the synthesis of many lipids (for example: steroid hormones) and for the neutralization of various harmful substances.

electron micrograph

1 - vacuoles and tubules of smooth ER. There are no ribosomes on their surface facing the hyaloplasm. but

enzymatic systems of synthesis and modification are connected here

lipid cations.

Other structures:
2 - mitochondria.
3 - peroxisome,

4 - ribosomes.
5 - residual body.

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 a large number ribosome.

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 type of smooth endoplasmic reticulum is also 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 the rough ER, synthesis and assembly of phospholipids and multi-chain proteins take place, 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.