Endoplasmic reticulum and ribosomes. Types of endoplasmic reticulum. Endoplasmic reticulum Formation of the endoplasmic reticulum

The organelles of this group include ribosomes, the Golgi complex, lysosomes, peroxisomes. They carry out the synthesis of organic compounds, their transport in the process of chemical refinement from one section of the tubular network to another, the accumulation, movement, packaging and exocytosis of finished synthesis products.

Endoplasmic reticulum and ribosomes. The endoplasmic reticulum is represented by tubules and cisterns, which anastomose and form a three-dimensional network in the hyaloplasm. The network consists of granular (containing ribosomes on the outer surfaces of the membranes) and agranular (without ribosomes) regions.

Ribosomes synthesize a variety of cellular proteins. At the optical level, ribosomes are indistinguishable; their number in a cell can be judged by the intensity of staining of the cytoplasm with general histological (basophilia) or special histochemical reagents and fluorochromes marking RNA. At the submicroscopic level, ribosomes look like osmiophilic black dots (about 20-25 nm in diameter), and their working complexes - polysomes - look like groups, or rosettes, of osmiophilic dots.

Ribosome components are created in different parts of the cell: ribosomal RNA is synthesized in the nucleolus; ribosomal proteins - in the cytoplasm. The latter enter the nucleus, where they are complexed with RNA molecules and combined into ribosomal subunits. Then the RNA subunits are transported from the nucleus through the pores and are in the cytoplasm either in a dissociated (inactive) or associated with each other (active) state. Working organelles consist of two associated (small and large) subunits, which are held in a reversibly bound state with the help of magnesium cations. A large subunit of ribosomes is formed by various RNA molecules with a complex secondary and tertiary structure, in combination with ribosomal proteins. The large subunit is much larger than the small one and has the shape of a hemisphere. The small subunit looks like a small cap. When subunits are associated into a ribosome, a regular interaction of their surfaces occurs.

between subunits of the working ribosomes there is a strict "division of labor" - the small subunit is responsible for binding messenger RNA, the large one is responsible for the formation of the polypeptide chain. In the cell, non-functioning ribosomes are in a dissociated state, and therefore they get the opportunity to constantly exchange subunits and constantly renew themselves. In the operating mode, ribosomes (from 3 to 20-30 in a group) form a stable complex - a polysome, in which they are connected by a messenger RNA thread.

The degree of development in the cell can be judged by the basophilia of the cytoplasm due to the presence of a large number of ribosomes; agranular areas of the endoplasmic reticulum are not detected at the light-optical level. In most cells, a granular network predominates, and both types of networks have a diffuse organization - their elements are located freely in the hyaloplasm, without any order. Protein synthesis in the granular network occurs on ribosomes and polysomes, and its channels and tanks are the receptacle and highways for moving the protein to the Golgi complex for completion.

Width and number of tubules and cisterns of the network in cells vary depending on their functional state - with an increase in functional loads on the cell, the tubules and cisterns of the network become multiple and expand significantly. The tubules of the endoplasmic reticulum are directly connected to the perinuclear space of the cell.

Meaning granular endoplasmic reticulum consists in the synthesis of membrane proteins and proteins intended "for export" and necessary for other cells, or used in extracellular physiological reactions. This type of network is present in all cells of the human body (except for mature sperm), but is most developed in those cells that are specialized in the synthesis of large amounts of protein molecules. There are relatively few such types of cells in the human body. An example is plasma cells that synthesize antibodies (or immunoglobulins); pancreatic cells that produce a complex of protein digestive enzymes (pancreatic juice); hepatocytes that synthesize a wide range of blood plasma proteins, coagulation and anticoagulation systems, as well as some other cells. In these cells, the tubules of the network are arranged in an orderly manner (in some cases, strictly parallel) in the form of the so-called ergastoplasm.

In undifferentiated and unspecialized cells granular endoplasmic reticulum, as a rule, is poorly developed, free poly- and ribosomes predominate in the cell structure, providing the synthesis of proteins necessary for the cell for growth and differentiation.

Agranular endoplasmic reticulum has the appearance of short tubules and vesicles (vesicles), which are diffusely located throughout the hyalosphere. In most cells, elements of the agranular network are, as a rule, not numerous. In cells that produce steroid hormones (cells of the adrenal glands, gonads), the agranular network is well developed and its numerous vesicles occupy large areas or form clutches around lipid inclusions - the precursors of steroid hormones. The membranes of the network contain the enzymes of steroidogenesis.

Apart from steroidogenesis, it is involved in the synthesis and metabolism of lipids, polysaccharides, triglycerides, the process of detoxification of metabolic products of drugs and endogenous cellular poisons. Large reserves of calcium cations are deposited in the tubules of the agranular network.

Endoplasmic reticulum (ER) or endoplasmic reticulum (ER) discovered only with the advent of the electron microscope. EPS is found only in eukaryotic cells and is a complex system of membranes that form flattened cavities and tubules. All together it looks like a network. EPS refers to single-membrane cell organelles.

EPS membranes extend from the outer membrane of the nucleus and are similar in structure to it.

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

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

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

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

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

It should be kept in mind that not all cell proteins are synthesized on the rough ER. A part (usually smaller) is synthesized by free ribosomes in the hyaloplasm, such proteins are used by the cell itself. Their signal sequence is not synthesized as unnecessary.

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

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

The structure, volume and functionality of the endoplasmic reticulum of the cell is not constant throughout the cell cycle, but is subject to certain changes.

Endoplasmic reticulum - a set of membrane channels and cavities that permeate the entire cell. On the granular ER, protein synthesis takes place (granules are ribosomes), on the smooth one, the synthesis of lipids and carbohydrates. Inside the ER channels, synthesized substances are accumulated and transported throughout the cell.

The Golgi apparatus is a stack of flat membrane cavities surrounded by vesicles. Through the EPS channels, substances enter the AG, where they accumulate and are chemically modified. Then the finished substances are enclosed in vials and sent to their destination.

Lysosomes are sacs filled with digestive enzymes. Formed in the Golgi apparatus. After the fusion of the lysosome with the phagocytic vesicle, a digestive vacuole is formed. In addition to food, lysosomes can digest waste parts of the cell or entire cells.

Ribosomes - the smallest organelles of the cell, consist of two subunits, chemically - from rRNA and proteins, are formed in the nucleolus. Function - protein synthesis.

The cell center consists of two centrioles that form the spindle during cell division. During interphase, centrioles are the center of organization of microtubules that form the cytoskeleton.

Tests

1. A single apparatus for protein biosynthesis
A) endoplasmic reticulum and ribosomes
B) mitochondria and cell center
C) chloroplasts and the Golgi complex
D) lysosomes and plasma membrane

2. In ribosomes located on the granular membranes of the endoplasmic reticulum,
A) photosynthesis
B) chemosynthesis
B) ATP synthesis
D) protein biosynthesis

3. During mitosis, the cell center is responsible for
A) spindle formation
B) spiralization of chromosomes
C) protein biosynthesis
D) movement of the cytoplasm

4. The process takes place in the ribosomes of an animal cell
A) protein biosynthesis
B) carbohydrate synthesis
B) photosynthesis
D) ATP synthesis

5. What is the function of the cell center in the cell
A) takes part in cell division
B) is the custodian of hereditary information
B) responsible for protein synthesis
D) is the center of template synthesis of ribosomal RNA

6. In ribosomes, unlike the Golgi complex,
A) carbohydrate oxidation
B) synthesis of protein molecules
C) the synthesis of lipids and carbohydrates
D) oxidation of nucleic acids

7. What is the function of the cell center in the cell?
A) forms large and small subunits of ribosomes
B) forms spindle fibers
C) synthesizes hydrolytic enzymes
D) accumulates ATP in interphase

8. Centriole, as a cell organoid, is
A) the primary constriction of the chromosome
B) the structural unit of the Golgi apparatus
C) structural unit of the cell center
D) small subunit of the ribosome

9. The system of flat tanks with tubes extending from them, ending in bubbles, is
A) core
B) mitochondrion
B) cell center
D) Golgi complex

10. In the Golgi complex, unlike chloroplasts,
A) transport of substances
B) oxidation of organic substances to inorganic
C) the accumulation of substances synthesized in the cell
D) synthesis of protein molecules

11. The similarity of the functions of lysosomes and mitochondria lies in what happens in them
A) enzyme synthesis
B) synthesis of organic substances
B) reduction of carbon dioxide to carbohydrates
D) breakdown of organic substances

12. Organic substances in the cell move to the organelles along
A) the vacuole system
B) lysosomes
B) endoplasmic reticulum
D) mitochondria

13. The similarity of the endoplasmic reticulum and the Golgi complex is that in their cavities and tubules
A) protein synthesis occurs
B) substances synthesized by the cell accumulate
C) substances synthesized by the cell are oxidized
D) the preparatory stage of energy metabolism is carried out

14. Lysosomes in a cell are formed in
A) endoplasmic reticulum
B) mitochondria
B) cell center
D) Golgi complex

15. The Golgi complex is NOT involved in
A) the formation of lysosomes
B) the formation of ATP
C) the accumulation of secrets
D) transport of substances

16. Lysosome enzymes are formed in
A) the Golgi complex
B) endoplasmic reticulum
B) plastids
D) mitochondria

17. In animal cells, polysaccharides are synthesized in
A) ribosomes
B) lysosomes
B) endoplasmic reticulum
D) core

18. Macromolecules of organic substances in the cell are broken down to monomers in
A) endoplasmic reticulum
B) lysosomes
B) chloroplasts
D) mitochondria

19. Membrane system of tubules penetrating the entire cell
A) chloroplasts
B) lysosomes
B) mitochondria
D) endoplasmic reticulum

20. The Golgi complex in a cell can be recognized by the presence in it
A) cavities and tanks with bubbles at the ends
B) an extensive system of tubules
B) cristae on the inner membrane
D) two membranes surrounding many facets

21. What is the function of lysosomes in the cell
A) break down biopolymers into monomers
B) oxidize glucose to carbon dioxide and water
B) carry out the synthesis of organic substances
D) carry out the synthesis of polysaccharides from glucose

22. The endoplasmic reticulum can be recognized in a cell by
A) a system of interconnected cavities with bubbles at the ends
B) the set of grains located in it
B) a system of interconnected branched tubules
D) numerous cristae on the inner membrane

23. The movement of substances in the cell is carried out with the participation
A) endoplasmic reticulum
B) lysosomes
B) mitochondria
D) chloroplasts

24. Substances synthesized in the cell are accumulated and then excreted
A) core
B) mitochondria
B) ribosomes
D) Golgi complex

25. What organelles are involved in the packaging and removal of substances synthesized in the cell?
A) vacuoles
B) Golgi apparatus
B) lysosomes
D) endoplasmic reticulum

26) In what organelle does the accumulation, packaging and removal of digestive enzymes from the cell take place?
A) in the cell center
B) in the ribosome
B) in the endoplasmic reticulum
D) in the Golgi complex

27. In what organelle do proteins, fats and carbohydrates synthesized in the cell accumulate?
A) lysosome
B) Golgi complex
B) ribosome
D) mitochondria

28. Lysosome is a
A) a system of interconnected tubules and cavities
B) an organoid delimited from the cytoplasm by one membrane
C) two centrioles located in the compacted cytoplasm
D) two interconnected subunits

QUESTIONS AND TASKS FOR REVIEW

Question 1. What are the main structural features of a eukaryotic cell?

The main feature of a eukaryotic cell is that its genetic material is surrounded by a membrane consisting of two membranes, i.e., the presence of a nucleus. The eukaryotic cell has internal membranes and a cytoskeleton formed by a system of microtubules and protein fibers.

Question 2. What cell structures are called inclusions? Give examples.

Inclusions are called non-permanent structures of the cytoplasm, which, unlike organelles, either appear or disappear during the life of the cell. Most often, they serve as a reserve of nutrients or are the products of vital activity of cell structures. Dense inclusions are called granules (grains of starch or glycogen). There are also liquid inclusions (drops of fat).

Question 3. What underlies the structural organization of the cell?

The cell is inherent in the membrane principle of structure. This means that the cell consists mainly of membranes with a similar structure, represented by a bimolecular layer of phospholipids, in which various protein molecules are immersed at different depths on both sides.

Question 4. How are cell membranes arranged?

A biological membrane is a bimolecular layer of phospholipids, into which various protein molecules are immersed at different depths from the outside and inside. The thickness of such a membrane is about 7.5 nm. Some protein molecules penetrate the membrane through and through, forming channels - the pores of the membrane. All cell membranes have a single structural plan and differ from each other only in the composition of their proteins - enzymes, receptors, etc.

Question 5. What functions does the outer cytoplasmic membrane perform?

The outer cytoplasmic membrane performs a number of functions:

1. Barrier. The outer cytoplasmic membrane separates the contents of the cell from the environment.

2. Transport. Active and passive transport of substances into and out of the cell occurs through the cell membrane.

Z. Structural. The outer cell membrane in a multicellular organism provides contact between adjacent cells. It is an integral and organizing part of all cells.

4. Receptor. Glycoprotein receptors are located on the outer surface of the membrane.

Question 6. In what ways is the exchange of substances between the cell and the environment carried out? What is pinocytosis? What is phagocytosis?

The transfer of substances through a semipermeable cell membrane can be carried out both through passive and active transport. Passive transport is simple diffusion along a concentration gradient; runs without energy consumption. Thus, substances with a very low molecular weight can enter the cell. These are water molecules, separate cations and anions. Active transport requires energy and occurs through the penetration of molecules and ions through the protein pores of the cell membrane. For example, Na and K cations. In addition to these pathways, large particles can be absorbed by the cell by phage and pinocytosis. A protrusion is formed in the cell membrane, the edges of which close, capturing liquid in the case of linocytosis, or a solid particle in phagocytosis. Both of these processes also come with energy costs.

Question 7. List the organelles of the cell and indicate their functions.

List the organelles of the cell and indicate their functions.

Organelles - constantly present in the cytoplasm, specialized to perform certain functions of the structure. According to the principle of organization, membrane and non-membrane cell organelles are distinguished.

Membrane cell organelles

1. Endoplasmic reticulum (EPSS is a system of internal cytoplasmic membranes that form large cavities - tanks and numerous tubules; occupies a central position in the cell, around the nucleus. EPSS makes up to 50% of the volume of the cytoplasm. EPSS channels connect all cytoplasmic organelles and open into the perinuclear space of the nuclear membrane Thus, EPS is an intracellular circulatory system.

There are two types of membranes of the endoplasmic reticulum - smooth and rough (granular). However, it must be understood that they are part of one continuous endoplasmic reticulum. Ribosomes are located on granular membranes, where protein synthesis takes place. Enzyme systems involved in the synthesis of fats and carbohydrates are ordered on smooth membranes.

2. The Golgi apparatus is a system of tanks, tubules and vesicles formed by smooth membranes. This structure is located on the cell periphery in relation to the EPS. On the membranes of the Golgi apparatus, enzyme systems are ordered, which are involved in the formation of more complex organic compounds from proteins, fats and carbohydrates synthesized in the EPS. This is where membranes are assembled and lysosomes are formed. The membranes of the Golgi apparatus provide for the accumulation, concentration and packaging of the secret released from the cell.

3. Lysosomes are membrane organelles containing up to 40 proteolytic enzymes capable of breaking down organic molecules. Lysosomes are involved in the processes of intracellular digestion and apoptosis (programmed cell death).

4. Mitochondria - energy stations of the cell. Two-membrane organelles having a smooth outer and inner membrane, forming cristae - ridges. Enzyme systems involved in the synthesis of ATP are ordered on the inner surface of the inner membrane. Mitochondria contain a circular DNA molecule similar in structure to the chromosome of prokaryotes. There are many small ribosomes on which protein synthesis is partially independent of the nucleus. However, the genes contained in the circular DNA molecule are not enough to ensure all aspects of the life of mitochondria, and they are semi-autonomous structures of the cytoplasm. An increase in their number occurs due to division, which is preceded by the doubling of the circular DNA molecule.

5. Plastids - organelles characteristic of plant cells.

There are leukoplasts - colorless plastids, chromoplasts with a red-orange color, and chloroplasts - green plastids. All of them have a single structural plan and are formed by two membranes: the outer (smooth) and the inner, forming partitions of the stroma thylakoid. On the thylakoids of the stroma there are grana, consisting of flattened membrane vesicles - grana thylakoids, stacked one on top of the other like coin columns. Inside the thylakoids of the grana is chlorophyll. The light phase of photosynthesis takes place here - in the grains, and the reactions of the dark phase - in the stroma. Plastids have a ring-shaped DNA molecule, similar in structure to the prokaryotic chromosome, and many small ribosomes, on which protein synthesis is partially independent of the nucleus. Plastids can pass from one species to another (chloroplasts to chromoplasts and leukoplasts), they are semi-autonomous cell organelles. The increase in the number of plastids is due to their division in two and budding, which is preceded by re. duplication of a circular DNA molecule.

non-membrane cell organelles

1. Ribosomes - rounded formations of two subunits, consisting of 50% of RNA and 50% of proteins. Subunits are formed in the nucleus, in the nucleolus, and in the cytoplasm, in the presence of Ca2+ ions, they combine into integral structures. In the cytoplasm, ribosomes are located on the membranes of the endoplasmic reticulum (granular ER) or freely. In the active center of ribosomes, the process of translation occurs (selection of tRNA anticodons to nRNA codons). Ribosomes, moving along the mRNA molecule from one end to the other, sequentially make mRNA codons available for contact with tRNA anticodons.

2. Centrioles (cell center) are cylindrical bodies, the walls of which are 9 triads of protein microtubules. In the cell center, the centrioles are located at right angles to each other. They are capable of self-reproduction on the principle of self-assembly. Self-assembly - the formation of structures similar to existing ones with the help of enzymes. Centrioles take part in the formation of spindle fibers. Provide the process of divergence of chromosomes during cell division.

Z. Flagella and cilia - organelles of movement; they have a single structure plan - the outer part of the flagellum faces the environment and is covered with a section of the cytoplasmic membrane. They are a cylinder: its wall is 9 pairs of protein microtubules, and two axial microtubules are located in the center. At the base of the flagellum, located in the ectoplasm - the cytoplasm that lies directly under the cell membrane, another short microtubule is added to each pair of microtubules. As a result, a basal body is formed, consisting of nine triads of microtubules.

4. The cytoskeleton is represented by a system of protein fibers and microtubules. Provides maintenance and change in the shape of the cell body, the formation of pseudopodia. Responsible for amoeboid movement, forms the inner frame of the cell, ensures the movement of cellular structures through the cytoplasm.

Question 8. What is the difference between smooth and rough membranes of the endoplasmic reticulum?

The endoplasmic reticulum is an intracellular circulatory system. There are two types of membranes of the endoplasmic reticulum - smooth and rough (granular). However, it must be understood that they are all part of one continuous endoplasmic reticulum. Ribosomes are located on rough membranes where protein synthesis takes place. Enzyme systems involved in the synthesis of fats and carbohydrates are ordered on smooth membranes.

Question 9. What cell organelles contain DNA and are capable of self-reproduction?

Mitochondria and plastids are semi-autonomous cell organelles containing DNA and capable of self-replication.

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 (connective tissue cells producing collagen protein), and plasma cells (producing immunoglobulins) is highly developed.

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 a large number of specific enzymes inside, and vesicles - small, membrane-surrounded vesicles, mainly located next to the 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 tissue 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.