intercellular adhesion, cell mobility, the formation of cytoplasmic increases (microwaves, stereociles, cilia, cinema).

Myofibrilla is a non-emblem contractile organella, consists of orderly packaged thin (actin), thick (mosic) threads and associated auxiliary proteins that form an actomyosic chemomechanical transducer and ensuring a reduction in myofibrils in skeletal muscle fibers and heart muscle cells (cardiomyocytes).

AXONEMA - NEMBRAND SHIPPING ORGELLALLA - the main structural element of the cilia and burning. The axonma consists of 9 peripheral pairs of microtubules and two centrally located microtubes. Hollowed by the ATPHASIC Activity of the Dienein protein - the component of the tubululdineine chemomechanical converter - is part of the handles associated with peripheral microtubes. The matrix for the account of the axonma is the basal Taurus - an analogue of the centriol.

Proteosoma is a functional macrocomplex of merqueous multifactylitian proteinases, widespread in the cytoplasm of eukaryot cells. Proteosomes regulate the degradation of intracellular proteins involved in various cellular processes (reproduction, growth, differentiation, functioning), and urgen the removal of damaged, oxidized and aberrant proteins.

Apoptosome - heptamer wheel-like structure- functional macrocomplex, activating caspase during apoptosis (adjustable cell death).

Inclusions are formed as a result of cell life. These can be pigment inclusions (melanine), nutrient and energy (lipids, glycogen, yolk), decay products (hemosiderin, lipofuscin).

Plasma membrane

Molecular composition

All biological membranes have common structural features and properties. According to the liquid-mosaic model, proposed in 1972 by Nicholsons and Singer, the plasma membrane is a liquid dynamic system with the mosaic location of proteins and lipids. According to this model,

the protein molecules are floating in a liquid phospholipid bisal, forming a kind of mosaic in it, but since the bilayer has a certain fluidity, then the mosaic pattern itself is not rigidly fixed; Proteins can change their position in it. The thickness of the plasma membrane is approximately 7.5 nm (Fig. 2-2).

The membrane base is a bilipid layer; Both lipid layers are formed by phospholipids. Phospholipids - triglycerides, in which one residue of fatty acid is replaced by the residue of phosphoric acid. The plot of the molecule in which the residue of phosphoric acid is is called a hydrophilic head; A plot in which there are residues of fatty acids - a hydrophobic tail. Fatty acids in the composition of hydrophobic tails are saturated and unsaturated. In the molecules of unsaturated acids, there are "freshers", which makes the packaging of bilayer more loose, and the membrane is more fluid. In the membrane, phospholipid molecules are strictly oriented in space: the hydrophobic ends of the molecules are addressed to each other (from water), and the hydrophilic heads outside (to water). Lipids are up to 45% of the mass of membranes.

Cholesterol is extremely important not only as a component of biological membranes; Based on cholesterol, the synthesis of steroid hormones - genital, glucocorticoids, mineralcorticoids occurs. Cholesterol is involved in the formation of rafts (dams) - discrete membrane domains rich in sphingolipids and cholesterol. Rafts are The liquid-ordered phase (section of swept-packed lipids) and have a density and melting point different from plasmolemma, so that they can "swim" - move in the plane of the liquid-disordered plasmolemma to perform certain functions.

In addition to lipids, the membrane includes proteins (on average up to 60%). They are

the majority of the specific functions of the membrane are determined;

- peripheral proteins are located on the outer or inner surface of the bilipide layer;

- semi-integrated proteins are partially immersed in a lipid bilipid layer on different depth;

- transmembrane, or integral proteins permeate the membrane through.

The carbohydrate component of membranes (up to 10%) is represented by oligosaccharide or polysaccharide chains, covalently associated with protein molecules

(glycoproteins) or lipids (glycolipids). Oligosaccharide chains protrude on the outer surface of the bilipide layer and form a superficial sheath with a thickness of 50 nm - glycocalix.

Functions of plasma membrane

The main functions of Plasmalamma: transmembrane vehicles of substances, endocytosis, exocytosis, intercellular information interactions.

Transmembrane transport substances. Transport of substances through the plasma membrane is a double-sided movement of substances from cytoplasm into extracellular space and back. Transmembrane transport provides delivery to the cell of nutrients, gas exchange, the elimination of metabolic products. The transfer of substances through the bilipid layer occurs by diffusion (passive and lightweight) and active transport.

Endocytosis - absorption (interpalization) of the water cell, substances, particles and microorganisms. Endocytosis also occurs when restructuring or destruction of the sections of the cell membrane. The morphologically distinguished embodiments of endocytosis include pinocytosis, phagocytosis, mediated by endocytosis receptors with the formation of bubble bubbles and clatrine-independent endocytosis with the participation of Kavol.

Exocytosis (secretion)- The process when intracellular secretory vesicles (single-dimmable bubbles) merge with plasmolm, and their contents are released from the cell. With constitutive (spontaneous) secretion, the merger of secretory bubbles occurs as they are formation and accumulation under the plasmolm. Adjustable exocytosis is started with the help of the signal, most often due to an increase in the concentration of calcium ions in the cytosol.

Intercellular information interactions. Cell, perceiving various signals, responds to changes in its environment by changing the functioning mode. The plasma membrane is the place of application of physical (for example, light quanta in photoreceptors), chemical (for example, flavoring and olfactory molecules, pH), mechanical (for example, pressure or tensile in mechanoreceptors) irritants of the outer medium and information molecules of an informational nature from the inner environment of the body. Signal molecules (ligands) (hormones, cytokines, chemokins) specifically bind to the receptor

High molecular weight, built-in plasmolm. The target cell using the receptor is able to recognize the ligand and respond to changing the functioning mode when binding to this ligand with its receptor. Receptors of steroid nature hormones (for example, glucocorticoids, testosterone, estrogen), tyrosine and retinic acid derivatives are localized in cytosol.

Plasma membrane, structure and functions. Structures formed by plasma membrane

We will begin histology with the study of the eukaryotic cell, which is the simplest system endowed with life. In the study of the cell in the light microscope, we obtain information about its size, form, and this information is associated with the presence of bounded membranes in cells. With the development of electron microscopy (EM), our ideas about the membrane, as a clearly limited section of the section between the cell and the environment, has changed, for it turned out that there is a complex structure on the cell surface, consisting of the following 3 components:

1. Complete component (glycocalix) (5 - 100 nm);

2. Plasma membrane (8 - 10 nm);

3. Submembered component (20 - 40 nm).

At the same time, 1 and 3 components are variable and depend on the type of cells, the structure of the plasma membrane is most static, which we will consider.

Plasma membrane.The study of Plasmolemma under the conditions of the EM led to the conclusion about the same type of its structural organization, in which it has the form of a triluminar line, where the inner and outer layers of electron transparent, and located between them - the wider layer seems to be electron transparent. This type of structural organization of the membrane indicates its chemical heterogeneity. Without touching the discussion on this issue, we will discuss that the plasmolm consists of three types of substances: lipids, proteins and carbohydrates.

Lipidsincluded in the membranes possess amphilic properties Due to the presence in their composition both hydrophilic and hydrophobic groups. The amphipatic nature of the lipids of the membrane contributes to the formation of lipid bilayer. At the same time, in phospholipids, the membranes allocate two domains:

but) phosphate - the head of the molecule, the chemical properties of this domain determine its solubility in water and is called hydrophilic;

b) acyl chains, representing esterified fatty acids - this hydrophobic domain.

Types of membrane lipids: The main class of lipids of biological membranes are phospholipids, they form the framework of the biological membrane. See Fig.1

Fig. 1: Types of membrane lipids

Biomembranes - this is a double layer amphipal lipids (lipid bilayer). In an aqueous medium, such amphiphilic molecules spontaneously form a bissoly, in which the hydrophobic parts of molecules are oriented towards each other, and hydrophilic water. See fig. 2.

Fig. 2: Biomembrane structure

The membrane includes lipids of the following types:

1. Phospholipids;

2. Sphingolipid - "Heads" + 2 hydrophobic "tail";

3. Glycolipids.

Cholesterol (hl)- located in the membrane mainly in the middle zone of Bisloy, it is amphiphilane and hydrophobic (With the exception of one hydroxy group). Lipid composition affects the properties of membranes: the ratio of the protein / lipids is close to 1: 1, but myelin shells are enriched with lipids, and internal membranes are proteins.

Methods for packing amphiphilic lipids:

1. Bisloi (lipid membrane);

2. Liposomes - this is a bubble with two layers of lipids, with both the inner and outer surfaces are polar;

3. Micelles - the third version of the organization of amphiphil lipids - a bubble, the wall of which is formed by one layer of lipids, and their hydrophobic ends are addressed to the center of micelles and their internal environment is not water, but hydrophobic.

The most common form of packaging of lipid molecules is education flat Bilaying membranes. Liposomes and micelles are fast transport forms that ensure the transfer of substances into the cage and from it. In medicine, liposomes are used to transfer water-soluble, and micelles - to transfer fat-soluble substances.

Membrane proteins

1. Integral (included in lipid layers);

2. Peripheral. See fig. 3.

Integral (transmembrane proteins):

1. Monotopic- (for example, Glycoforin. They crosses the membrane 1 time), and are receptors, while their outdoor domain - relates to a recognizing part of the molecule;

2.Polytonian- repeatedly permeate the membrane - this is also receptor proteins, but they activate the transmission path of the signal inside the cell;

3.Lipid-related membrane proteins;

4. Membrane proteins, tied with carbohydrates.

Fig. 3: Membrane proteins

Peripheral proteins:

Not immersed in lipid bilayer and are not connected to him covalently. They are held at the expense of ionic interactions. Peripheral proteins are associated with integrated proteins in the membrane due to interaction - protein protein interaction.

1. Spectrinewhich is located on the inner surface of the cell;

2.Fibronctin, Localized on the outer surface of the membrane.

Proteins - Usually up to 50% of the mass of the membrane. Wherein integral proteins perform the following functions:

a) proteins of ion channels;

b) receptor proteins.

BUT peripheral membrane proteins (fibrillary, globular) perform the following functions:

a) external (receptor and adhesive proteins);

b) Internal - cytoskeleton proteins (spectrine, ankirine), proteins of the second intermediaries system.

Ion canals- These are the channels formed by integrated proteins, they form a small time, through which ions pass through an electrochemical gradient. The most famous channels are channels for NA, K, CA, CL.

There are water channels - it aquroporins (erythrocytes, kidneys, eyes).

Complete component - Glycocalix, thickness 50 nm. These are carbohydrate portions of glycoproteins and glycolipids, providing a negative charge. Under the EM is a loose layer of moderate density, covering the outer surface of the plasmolemma. In addition to carbohydrate components, in addition to carbohydrate components, it includes peripheral membrane proteins (semi-integrated). The functional sections of them are in the above-handed zone - these are immunoglobulins. See fig. four

Glycicalis function:

1. Play role receptors;

2. Intercellular recognition;

3. Intercellular interactions (adhesive interactions);

4. Guest receptors;

5. Enzyme adsorption zone (trim digestion);

6. Gormone receptors.

Fig. 4: Glycocalix and subable proteins

Submembered component - the outer zone of the cytoplasm, usually has relative rigidity and this zone is especially rich in filaments (D \u003d 5-10 nm). It is assumed that the integral proteins that are included in the cell membrane are directly or indirectly associated with actin filaments lying in the subable zone. At the same time, it was experimentally proved that in the aggregation of integral proteins, which in this area, Aktin and MIOSIN also aggregate, which indicates the participation of actin filament in the regulation of the cell form.

The kernel is responsible for storing the genetic material recorded on DNA, and also manages all cell processes. The cytoplasm contains organides, each of which has its own functions, such as, for example, the synthesis of organic substances, digestion, etc. And we will talk about the last component in more detail in this article.

in biology?

In simple language, this is a shell. However, it is not always completely impenetrable. Almost always transported certain substances through the membrane.

In cytology, the membrane can be divided into two main types. The first is a plasma membrane that covers the cell. The second is the organoid membranes. There are organelles that possess one or two membranes. Singlembrane includes endoplasmic reticulum, vacuoles, lysosomes. Two families belong plasts and mitochondria.

Also, membranes can be inside organoids. These are usually derivatives of the inner membrane of two-paved organoids.

How are the membranes of two-grated organoids?

The plastic and mitochondria have two shells. The outer membrane of both organoid is smooth, but the internal forms the structure necessary for the functioning of the organoid structure.

So, the shell mitochondria has acts inside - crystami or ridges. On them and the cycle of chemical reactions required for cellular respiration occurs.

Derivatives of the inner membrane of chloroplasts are disco-shaped bags - thylacoids. They are collected in stacks - marriage. Separate marriages are combined with lamella - long structures, also formed from membranes.

The structure of the membrane of single-dimmable organoids

Such an organelle membrane has one. It is usually a smooth shell consisting of lipids and proteins.

Features of the structure of the plasma membrane cells

The membrane consists of such substances as lipids and proteins. The structure of the plasma membrane provides its thickness of 7-11 nanometers. The bulk of the membrane is lipids.

The structure of the plasma membrane provides for the presence of two layers in it. The first is a double layer of phospholipids, and the second is a layer of proteins.

Lipids of plasma membrane

Lipids, which are part of the plasma membrane, are divided into three groups: steroids, sphingophospolipids and glyceluphospholipids. The latter's molecule has in its composition the residue of the trochatomic alcohol of glycerol, in which the hydrogen atoms of two hydroxyl groups are substituted by chains of fatty acids, and the hydrogen atom of the third hydroxyl group is the residue of phosphoric acid to which, in turn, attaches the residue of one of the nitrous bases.

The glider phospholipid molecule can be divided into two parts: head and tails. Hydrophilin head (i.e. dissolves in water), and tails - hydrophobic (they repel water, but dissolved in organic solvents). Due to this structure, the glyceluchospiripid molecule can be called amphiphilic, i.e. and hydrophobic, and hydrophilic at the same time.

Sphingophospholipids are similar to the chemical structure on glyceluphospholipids. But they differ from those mentioned above in the fact that in their composition instead of the remnant of glycerol have the residue of Sphingosin alcohol. Their molecules also possess heads and tails.

The picture below is clearly visible the scheme of the plasma membrane structure.

Plasma membrane proteins

As for the proteins that are part of the plasma membrane, it is mainly glycoprotein.

Depending on the location in the shell, they can be divided into two groups: peripheral and integral. The first are those that are on the surface of the membrane, and the second are those that permeate the entire thickness of the shell and are inside the lipid layer.

Depending on the functions that proteins perform, they can be divided into four groups: enzymes, structural, transport and receptor.

All proteins that are in the structure of the plasma membrane are chemically not related to phospholipids. Therefore, they can freely move in the main layer of membranes, gather in groups, etc. That's why the structure of the plasma membrane cells cannot be called static. It is dynamic, as it changes all the time.

What role does the cell shell perform?

The structure of the plasma membrane allows it to cope with five functions.

The first and basic is the limitation of the cytoplasm. Due to this, the cell has a constant shape and size. Performance of this function is ensured due to the fact that the plasma membrane is strong and elastic.

The second role is the provision of plasma membranes due to its elasticity can form outgrowths and folds in the places of their compound.

The following feature of the cell shell is transport. It is provided at the expense of special proteins. Due to them, the necessary substances can be transported into the cell, and unnecessary - to be disposed of from it.

In addition, the plasma membrane performs an enzymatic function. It is also carried out thanks to the proteins.

And the last function is signal. Due to the fact that proteins under the influence of certain conditions can change their spatial structure, the plasma membrane can send the signal cells.

Now you know all about the membranes: what is a membrane in biology, what they are, how the plasma membrane and the organoid membranes are arranged, what functions they perform.

The cell membrane, which is also called plasma, cytlemma, or plasma membrane is a molecular structure that is elastic by its nature, which consists of various proteins and lipids. It separates the content of any cell from the external environment, thereby adjusting its protective properties, and also provides the exchange between the external environment and the cell internal content directly.

Plasmamama is a partition located inside, directly behind the shell. It divides the cage to certain compartments that are directed to the compartments or organelles. They contain specialized environmental conditions. The cell wall completely closes the entire cell membrane. It looks like a double layer of molecules.

Basic information

The composition of the plasmama is phospholipids or, as they are also called, complex lipids. Phospholipids have several parts: tail and head. Specialists call hydrophobic and hydrophilic parts: depending on the structure of an animal or vegetable cell. Plots that are referred to as the head are addressed inside the cell, and the tails are out. Plasmalemma according to the structure are invariating and very similar among various organisms; Most often, the exception can be archaei, in which partitions consist of various alcohols and glycerin.

Plasma thickness of approximately 10 nm.

There are partitions that are on the outside or outside the part, closely adjacent to the membrane - they are called superficial. Some types of protein can be peculiar contact points for cell membrane and shell. Inside the cell is a cytoskeleton and an outer wall. Certain types of integral protein can be used as channels in ion transport receptors (in parallel with nervous endings).

If you use an electronic microscope, then you can get data on the basis of which you can construct a structure of the structure of all parts of the cell, as well as the main components and shells. The upper apparatus will consist of three subsystems:

• comprehensive appropriate inclusion;
• the cytoplasm refractory apparatus, which will have a submembrane part.

This unit includes cell cytoskeleton. The cytoplasm with organoids and the nucleus is called a nuclear unit. Cytoplasmic or, differently, plasma cell membrane is under the cellular shell.

The word "membrane" occurred from the Latin word Membrum, which can be translated as "leather" or "shell". The term was offered more than 200 years ago and they were more often called the edges of the cell, but during the period when the use of various electronic equipment began, it was established that plasma cytlemmas constitute many different elements of the shell.

Elements most often structural, such as:

• mitochondria;
• lysosomes;
• plastdoms;
• partitions.

One of the first hypotheses relative to the molecular composition of Plasmamama was nominated in 1940 by the Scientific Institute of Great Britain. Already in 1960, William Roberts proposed the world a hypothesis "On Elementary Membrane". It assumed that all the plasmales of the cells consist of certain parts, in fact, are formed by the general principle for all the kingdoms of organisms.

At the beginning of the seventies of the XX century, many data were opened, on the basis of which in 1972, scientists from Australia proposed a new mosaic-liquid model of the cell structure.

The structure of the plasma membrane

The 1972 year model is generally recognized to this day. That is, in modern science, various scientists working with the shell are based on the theoretical work "The structure of the biological membrane of a liquid-mosaic model".

Protein molecules are associated with lipid bislock and permeate the entire membrane completely - integral proteins (one of the generally accepted names is transmembrane proteins).

The shell in the composition has various carbohydrate components that will look like a polysaccharide or saccharium chain. The chain, in turn, will be connected by lipids and protein. The chain protein molecules are called glycoproteins, and lipid molecules - glycosides. Carbohydrates are on the outside of the membrane and perform the functions of receptors in animal animal cells.

Glycoprotein - represent a complex of supembered functions. It is also called glycocalix (from the Greek words of the Glice and Calix, which means "sweet" and "cup"). The complex contributes to the adhesion of cells.

Functions of plasma membrane

Barrier

It helps to separate the inner components of the cell mass from those substances that are from the outside. Protects the body from different substances from entering various substances, which will be alien for it, and helps maintain intracellular balance.

Transport

The cell has its own "passive transport" and uses it to reduce energy consumption. The transport function works in the following processes:

• endocytosis;
• exocytosis;
• sodium and potassium exchange.

On the outside of the membrane is a receptor, on the plot of which the hormones and various regulatory molecules occur.

Passive transportation - The process in which the substance passes through the membrane, while the energy is not spent. In other words, the substance is delivered from a cell area with a high concentration, to the other side where the concentration will be lower.

There are two types:

• Simple diffusion - Inherent in small neutral H2O, CO2 and O2 molecules and some hydrophobic organic substances with a low molecular weight and, respectively, without any problems pass through the membrane phospholipids. These molecules can penetrate the membrane until the time until the concentration gradient is stable and unchanged.
• Light diffusion - characteristic of various hydrophilic type molecules. They can also pass through the membrane according to the concentration gradient. However, the process will be carried out using various proteins that will form specific channels of ionic connections in the membrane.

Active transport - It is the movement of various components through the membrane wall in counterweight gradient. Such transfer requires significant costs of energy resources in the cell. Most often, precisely active transport is the main source of energy consumption.

Several varieties isolated active transport with the participation of carrier proteins:

• Sodium-potassium pump. Obtaining a cell of the necessary minerals and microelements.
• Endocytosis - The process at which the seizure of solid particles (phagocytosis) is captured or different drops of any liquid (pinocytosis).
• Exocytosis - The process at which the excretion from the cell of certain particles into the outer environment is separated. The process is a counterweight endocytosis.

The term "endocytosis" occurred from the Greek words "End" (from the inside) and "ketosis" (bowl, compartler). The process characterizes the seizure of an external composition of the cell and is carried out in the production of membrane bubbles. This term was proposed in 1965 by Professor of Cytology from Belgium Christian Bails, he studied the absorption of various substances by mammalian cells, as well as phagocytosis and pinocytosis.

Phagocytosis

It occurs when the cell is captured by certain solid particles or alive cells. And pinocytosis is a process in which the liquid drops are captured by the cell. Phagocytosis (from the Greek Words "Eater" and "Capacity") - the process in which very small objects of wildlife is captured and absorbed, as well as solid parts of various single-cell organisms.

The discovery of the process belongs to the physiologist from Russia - Vyacheslav Ivanovich Mesnikov, who identified the process directly, while he conducted various tests with marine stars and tiny daphnia.

At the heart of the nutrition of single-cell heterotrophic organisms lies their ability to digest, as well as capture various particles.

Mechnikov described the absorption algorithm to the bacteria Ameject and the general principle of phagocytosis:

• adhesion - adhesion of bacteria to cell membrane;
• absorption;
• bubble formation with bacterial cell;
• opening a bubble.

Based on this, the phagocytosis process consists of such steps:

1. The absorbed particle is attached to the membrane.
2. Surroundings of the absorbed particle of the membrane.
3. Education of the membrane bubble (Fagomy).
4. Disposal of the membrane bubble (phagems) into the inner part of the cell.
5. Combining FAGOSOMES and lysosomes (digestion), as well as internal movement of particles.

You can observe a complete or partial digestion.

In the case of partial digestion, the residual caller is most often formed, which will be inside the cell for a while. Those remnants that will be undigested are removed (evacuated) from the cell by exocytosis. In the process of evolution, this feature of predisposition to phagocytosis was gradually separated and moved from various single-cellular to specialized cells (such as digestive in intestinal and sponges), and after special cells in mammals and humans.

Lymphocytes and leukocytes in the blood are predisposed to phagocytosis. The phagocytosis process itself needs high energy costs and is directly combined with the activity of the outer cell membrane and the lysosomes under which the digestive enzymes are located.

Pinocytosis

Pinocytosis is the seizure of a cell surface of any liquid in which there are various substances. The opening of the pinocytosis phenomena belongs to the scientist Fitzgerald Lewis. This event occurred in 1932.

Pinocytosis is one of the main mechanisms in which high molecular weight compounds fall into the cell, for example, various glycoproteins or soluble proteins. Pinocitotic activity, in turn, is impossible without the physiological state of the cell and depends on its composition and composition of the environment. We can observe the most active pinocytosis from Amoeba.

Pinocytosis has been observed in intestinal cells, in vessels, renal tubules, as well as growing oocytes. In order to depict the process of pinocytosis, which will be carried out using human leukocytes, it is possible to protrude the plasma membrane. At the same time, the parts will be taken off and separated. The process of pinocytosis needs energy.

Pinocytosis process stages:

1. Thin growths appear on the outer cell plasmalemma that they surround the liquid drops.
2. This section of the outer shell becomes thinner.
3. The formation of a membrane bubble.
4. The wall breaks through (fails).
5. The bubble moves in the cytoplasm and can merge with various bubbles and organoids.

Exocytosis

The term has occurred from the Greek words "Exo" - external, external and "cytosis" - a vessel, bowl. The process is to select the cellular part of certain particles into the external environment. The process of exocytosis is opposite to pinocytosis.

In the process of incocitosis from the cell bubbles of intracellular fluid flow and switch to the outer membrane of the cell. The contents inside bubbles may be released outward, and the cell membrane merges with the bubble shell. Thus, most macromolecular compounds will occur in this way.

Exocytosis performs a number of tasks:

• delivery of molecules to the outer cell membrane;
• transportation throughout the entire cell substances that will be needed for growth and increasing the area of \u200b\u200bthe membrane, for example, certain proteins or phospholipids;
• release or compound different parts;
• the removal of harmful and toxic products that appear in metabolism, for example, hydrochloric acid by the secreted cells of the gastric mucosa cells;
• transportation of pepsinogen, as well as signal molecules, hormones or neurotransmitters.

Specific functions of biological membranes:

• the generation of a pulse occurring at the nervous level inside the neuron membrane;
• synthesis of polypeptides, as well as lipids and carbohydrates with a rough and smooth network of the endoplasmic grid;
• changes in light energy and its conversion into chemical energy.

Video

From our video you will learn a lot of interesting and useful about the structure of the cell.

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The plasma membrane performs a number of essential functions:

1) Barrier. The plasma membrane barrier function is to limit the free diffusion of substances from the cell in the cell, preventing the leakage of the water-soluble contents of the cell. But since the cell should receive the necessary nutrients, allocate the finite products of metabolism, regulate intracellular concentrations of ions, then there are special mechanisms for transferring substances through the cell membrane.

2) Transport.The transport function refers ensuring the receipt and removal of various substances into the cell and from the cell. Important property of the membrane - electoral permeability, or semi-perception. It easily passes water and water-soluble gases and repels polar molecules, such as glucose or amino acids.

There are several transport mechanisms of substances through the membrane:

passive transport;

active transport;

transportation in membrane packaging.

Passive transport.Diffusion -this is the movement of particles of the medium, leading to the transfer of the substance from the zone, where its concentration is high to the low concentration zone. With diffusion transport, the membrane functions as an osmotic barrier. The diffusion rate depends on the magnitude of molecules and their relative solubility in fats. The smaller the dimensions of molecules and the more fat soluble (lipophils), the faster there will be moving through lipid bilayer. Diffusion can be neutral(transfer of uncharged molecules) and lightweight(With the help of special proteins of carriers). The speed of light diffusion is higher than neutral. Water has the maximum penetrating ability, since its molecules are small and uncharged. Diffusion of water through the cell membrane is called osmosis.It is assumed that in the cell membrane for the penetration of water and some ions there are special "pores". Their number is small, and the diameter is about 0.3-0.8 nm. A biseling molecule easily soluble in lipid molecules is most quickly diffusted through the membrane, for example, and uncharged polar small diameter molecules (CO, urea).

Transfer of polar molecules (sugars, amino acids), carried out using special membrane transport proteins is called light diffusion.Such proteins are detected in all types of biological membranes, and each particular protein is designed to transfer the molecules of a certain class. Transport proteins are transmembrants, their polypeptide chain crosses a lipid bilayer several times, forming through passages. This ensures the transfer of specific substances through the membrane without direct contact with it. There are two main class of transport proteins: proteins-carriers (conveyors)and channel-formingproteins (proteins-channels). Proteins-carriers tolerate molecules through the membrane, after changing their configuration. Channel-forming proteins are formed in the membrane filled pores. When the pores are open, the molecules of specific substances (usually inorganic ions of suitable size and charge) pass through them. If the molecule of the transported substance does not have a charge, the direction of transport is determined by the concentration gradient. If the molecule is charged, then the electrical charge of the membrane (membrane potential) affects its transport, except for the concentration gradient. The inner side of the plasmamama is usually charged negatively towards the outer. The membrane potential makes it easier to penetrate positively charged ions and prevents the passage of the ions of charged negative.

Active transport.Active transport is the transfer of substances against an electrochemical gradient. It is always carried out by proteins conveyors and closely connected with the source of energy. In carrier proteins there are binding sites with a transported substance. The more such sites binds to the substance, the higher the speed of transport. Selective transfer of one substance called unport.Transfer several substances motransport systems.If the transfer goes in one direction - this simportif in the opposite - antiport. For example, glucose from extracellular fluid into the cell is transferred to unime. The transfer of glucose and Na 4 from the intestinal cavity or kidney channels, respectively, in the intestinal cells or blood is simply carried out, and the transfer of C1 ~ and NSO "antiporttty. It is assumed that when transferring, reversible conformational changes occur in the conveyor, which allows you to prevail the connected substances with it. .

An example of a carrier protein that uses the energy to transport the substances elected during hydrolysis ATP is Na. + -TO + pump,detected in the plasma membrane of all cells. Na + -K Pump works on the principle of antiport, pumping Na "from the cell and to t inside the cell against their electrochemical gradients. The Na + gradient creates osmotic pressure, supports cellular volume and provides transportation of sugars and amino acids. A third of all energy is spent on the work of this pump Required for the life of the cells. When studying the mechanism of action Na +-k + pump, it was found that it is an enzyme atphase and transmembrane integral protein. In the presence of Na + and ATP under the action of ATPA from ATP, end phosphate is separated and attached to the absparagic acid residue. On the Atphase molecule. The Atphase molecule is phosphorylated, changes its configuration and Na + is derived from the cell. Following the removal of Na from the cell, there is always transport to "into the cell. For this, the previously attached phosphate is cleaved from the ATPase in the presence. The enzyme is dephosphorylated, restores its configuration and 1 "pumps" into the cell.

Atphaz is formed by two subunits, big and small. A large subunit consists of a thousand amino acid residues crossing the bilayer several times. It has catalytic activity and is capable of reversible phosphorylated and defosphorilated. A large subunit on the cytoplasmic side has areas for the binding of Na + and ATP, and on the outside of -pox to bind to + and Wabaina. A small subunit is a glycoprotein and the function is not yet known.

Na + -k Pump has an electrical effect. It removes three positively charged Na F ions from the cell and contributes to it two ions to as a result, a current flows through the membrane, forming an electric potential with a negative value in the inner part of the cell relative to its outer surface. Na "-k + pump regulates the cellular volume, controls the concentration of substances inside the cell, supports osmotic pressure, participates in the creation of membrane potential.

Transportation in membrane packaging. Transfer through a membrane of macromolecules (proteins, nucleic acids, polysaccharides, lipoproteins) and other particles is carried out by consistent education and merging surrounded by membrane bubbles (vesicul). The process of vesicular transport takes place in two stages. Initially, the membrane bubble and plasmalama sticks out, and then merge. For flowing 2, it is necessary for the water molecules to be displaced by interacting lipid bilayers, which are closer to 1-5 nm. It is believed that this process is activated by special fusion proteins(They are allocated for only viruses). Vesicular transport has an important feature - absorbed or secreted macromolecules that are in bubbles are usually not mixed with other macromolecules or cells of cells. Bubbles can merge with specific membranes, which ensures the exchange of macromolecules between the extracellular space and the contents of the cell. Similarly, the macromolecule was transferred from one cell compartment to another.

Transportation of macromolecules and particles in a cell called endocytosis.At the same time, transportable substances are enveloped by a part of the plasma membrane, a bubble (vacuole) is formed, which moves inside the cell. Depending on the size of the resulting bubbles, two types of endocytosis differ - pinocytosis and phagocytosis.

Pinocytosisprovides absorption of fluid and solutes in the form of small bubbles (D \u003d 150 nm). Phagocytosis -this is the absorption of large particles, microorganizes or wreckage of organelle, cells. At the same time, large bubbles, phagosomes or vacuoles (D-250 nm and more) are formed. The simplest phagocytic function is a power form. In mammals, phagocytic function is carried out by macrophages and neutrophils protecting the body from infection by absorbing invading microbes. Macrophages also participate in the disposal of old or damaged cells and their fragments (in the human body, macrophages absorb more than 100 old erythrocytes every day). Phagocytosis begins only when the absorbed particle contacts the phagocytic surface and activates specialized receptor cells. The binding of particles with the specific membrane receptors causes the formation of pseudopod, which envelop a particle and, merging by the edges, form a bubble - fagos.The formation of the FAGOSOMOMA and the actual phagocytosis occurs only if the particle is constantly in contact with plasmalemma receptors, as it were, "fastening zipper".

A significant part of the material absorbed by the cell by endocytosis finishes its path in the lysosomes. Large particles are included in fAGOSOMES,which then merge with lysosomes and form fagalisosomes.Liquid and macromolecules, absorbed in pinocytosis, are initially transferred to endosomes, which are also merged with lysosomes, forming endolysis. Those present in the lysosomes of various hydrolytic enzymes are quickly destroyed by macromolecules. Hydrolysis products (amino acids, sugar, nucleotides) are transported from lysosomes to cytosol, where they are used by the cell. Most membrane components of endocytosis bubbles from FAGOS and ENDOS are returned with the help of exocytosis to the plasma membrane and are recycled there. The main biological value of endocytosis is to obtain construction blocks due to intracellular digestion of macromolecules in lysosomes.

The absorption of substances in eukaryotic cells begins in the specialized areas of the plasma membrane, the so-called fought venge.On electronic micrographs, the yams look like a patch of plasma membrane, the cytoplasmic side of which is covered with a fibrous layer. The layer as it should be small than plasmamama. Snakes occupy about 2% of the total surface of the cell furnace eukaryot. For a minute, the pits grow, they are fought more deeply, drawn into the cage and then narrowing at the base, clench, forming bubbles. It has been established that from the plasma membrane of fibroblasts for one minute, about the fourth part of the membrane in the form of bounded bubbles is cleaved. Bubbles quickly lose their bubble and acquire the ability to merge with lysosome.

Endocytosis can be nonspecific(constitutive) and specific(receptor). For nonspecific endocytosisthe cage captures and absorbs the substances completely alien to it, for example, soot particles, dyes. Initially, the particles are precipitated on the plasma glycicalce. Positively charged groups of proteins are particularly precipitated (adsorbed), since the glycocalix carries a negative charge. Then the morphology of the cell membrane changes. It can either dive, forming phenomenon (invagination), or, on the contrary, form growing, which, as it were, separating the small volumes of the liquid medium. The formation of invaginations is more characteristic of the cells of the intestinal epithelium, AmeB, and the growths for phagocytes and fibroblasts. Block these processes can be inhibitors of breathing. Formed bubbles - primary endosome, can merge among themselves, increasing in size. In the future, they are connected to lysosomes, turning into an endolysis - digestive vacuol. The intensity of liquid-phase nonspecific pinocytosis is quite high. Macrophages form up to 125, and the cells of the subtle intestine epithelium are up to a thousand pinos per minute. Abundance Pinos leads to the fact that the plasmalemma is rapidly spent on the formation of a plurality of small vacuoles. The recovery of the membrane is pretty quickly during recycling in the process of exocytosis due to the return of vacuoles and embedding them into a plasma service. At the macrophages, the entire plasma membrane is replaced in 30 minutes, and in fibroblasts in 2 hours.

A more efficient way to absorb from extracellular fluid of specific macromolecules is specific endocytosis(receptors mediated). Macromolecules are associated with complementary receptors on the cell surface, accumulate in the bordered yam, and then forming an endosome, immersed in cytosol. Receptor endocytosis ensures accumulation of specific macromolecules at its receptor. Molecules that bind on the surface of a plasmamafe with a receptor are called ligands.With the help of receptor endocytosis in many animal cells, cholesterol is absorbed from extracellular medium.

Plasmolem takes part in the removal of substances from the cell (exocytosis). In this case, vacuoles are suitable for plasmolem. In places of contacts plasmolm and vacuole membrane, the vacuole's contents are merged into the environment. Some simple places in the cell membrane for exocytosis are predetermined. Thus, in the plasma membrane of some cilia infusories there are certain sections with the right location of large globes of integral proteins. The mucocyst and tricotist infusories are completely ready for secretion, on the top of the plasmamama there is a whin of the globul integral proteins. With these parts of the membrane, mucocyst and tricotist are in contact with the surface of the cell. A peculiar exocytosis is observed in neutrophils. They are capable of throwing their lysosomes into the environment under certain conditions. At the same time, in some cases, small grows of plasmamama containing lysosomes are formed, which then come off and go to Wednesday. In other cases, there is an invagination of the plasma-free cell and capture it with lysosomes, placed far from the cell surface.

The processes of endocytosis and exocytosis are carried out with the participation of the fibrilular components of the cytoplasm associated with the plasmolemma.

Receptor plasma function.This is one of the main, universal cells for all cells, is the receptor function of the plasmamama. It determines the interaction of cells with each other and with an external environment ..

All variety of information intercellular interactions can be schematically represented as a chain of consecutive responses signal-receptor-secondary mediator response (Signal-answer concept).The transmission of information from the cell to the cell is carried out signal molecules that are produced in alone cells and specifically affect other signal sensitive (target cells). Signal molecule - primary mediatorit is associated with the receptors that are reacting only on target cells that are reacting only to certain signals. Signal Molecules - ligands -suitable for your receptor as the key to the castle. Ligands for membrane receptors (plasma receptors) are hydrophilic molecules, peptide hormones, neurotransmitters, cytokines, antibodies, and for nuclear receptors - fat-soluble molecules, steroid and thyroid hormones, vitamin D as receptors on the cell surface can be used by the membrane proteins or elements of glycicalis - Polysaccharides and glycoproteins. It is believed that plots sensitive to individual substances are scattered over the cell surface or collected in small zones. Thus, on the surface of prokaryotic cells and animal cells there is a limited number of places with which viral particles can be born. Membrane proteins (carriers and channels) recognize, interact and transfer only certain substances. Cell receptors are involved in the transmission of signals from the cell surface inside it. The variety and specificity of receptor sets on the cell surface leads to the creation of a very complex system of markers, allowing to distinguish their cells from others. Similar cells interact with each other, they can stick together (conjugation of the simplest, tissue formation in multicellular). Cells do not perceive markers, as well as characterized by a set of deterministic markers are destroyed or rejected. When forming a receptor-ligand complex, transmembrane proteins are activated: protein converter, protein amplifier. As a result, the receptor changes its conformation and interacts with the predecessor of the secondary intermediary in the cell - messenger.Messengers can be ionized calcium, phospholipase C, adenylate cyclase, guanillates. Under the influence of the messenger, the activation of enzymes involved in the synthesis cyclic Monophosphate - AMPor GMF.The latter change the activity of two types of protein kinase enzymes in cytoplasm cells leading to phosphorylation of numerous intracellular proteins.

The formation of the TSAMF, under the action of which the secretion of a row of hormones - thyroxine, cortisone, progesterone increases, increases the decay of glycogen in the liver and muscles, frequency and power of heart rate, osteo-etherection, reverse absorption of water in the Netron Canalces.

The activity of the adenylate cyclase system is very large - the synthesis of the CAMF leads to ten thousandth signal strengthening.

Under the action of TSGMF, the secretion of insulin by the pancreas, histamine fat cells, ferotonin platelet, is reduced by smooth muscle tissue.

In many cases, in the formation of the receptor-ligand complex, a membrane potential change occurs, which in turn leads to a change in the permeability of plasmama and metabolic processes in the cell.

The plasma membrane contains specific receptors that react to physical factors. Thus, in photosynthetic bacteria on the cell surface, chlorophylls are located responding to light. In photosensitive animals in the plasma membrane, there is a whole system of phonographic proteins-rhodopcins, with which the light irritant is transformed into a chemical signal, and then an electrical pulse.