Features of the structure, properties and functions of cell membranes. Cell membrane: Definition, Membrane Functions, Physical Properties

It's no secret that all living beings on our planet consist of their cells, these countless "" organic matter. In turn, the cells are in turn are surrounded by a special protective sheath - a membrane playing a very important role in the vital cells of the cell, and the function of the cell membrane is not limited to only the protection of the cell, but are a complex mechanism involved in breeding, nutrition, cell regeneration.

What is a cell membrane

The word "membrane" itself is translated from Latin as "film", although the membrane is not just a kind of film into which the cell is wrapped, but a combination of two films interconnected and possessing various properties. In fact, the cell membrane is a three-layer lipoprotein (oil-protein) shell separating each cell from neighboring cells and the environment, and performing controlled exchange between cells and the environment, so the academic definition of what is the cell membrane.

The meaning of the membrane is just huge, because it does not simply separate one cell from another, but also provides cellular interaction, both with other cells and the environment.

History of the study of the cell membrane

An important contribution to the study of the cell membrane was made by two German scientists and Grendel in the distant 1925. It was then that they managed to carry out a complex biological experiment over red blood tales - red blood cells, during which scientists got so called "shadows", empty erythrocyte shells, which lay down in one stack and measured the surface area, and also calculated the number of lipids in them. Based on the resulting number of lipids, scientists concluded that they are just enough on a double layer of cell membrane.

In 1935, another couple of researchers of the cell membrane, this time the Americans Daniel and Dawson after a whole series of long experiments set protein content in the cell membrane. Otherwise, it was impossible to explain why the membrane has such a high level of surface tension. Scientists have witnessed the cell membrane model in the form of a sandwich, in which homogeneous lipido-protein layers play the role of bread, and between them instead of oil - emptiness.

In 1950, with the advent of the electronic theory of Daniel and Dawson, it was possible to confirm the practical observations - on the micrographs of the cell membrane, layers of lipid and protein heads were clearly visible and also an empty space between them.

In 1960, American biologist J. Robertson developed the theory of the three-layer structure of cell membranes, which for a long time was considered the only true, but with the further development of science, doubts began to appear in her infallibility. So, for example, from the point of view of cells it would be difficult and difficult to transport the necessary useful substances through the entire "Sandwich"

And only in 1972, American Biologists S. Singer and Nicholson were able to explain the inconsistencies of Robertson's theory with the help of a new liquid-mosaic model of the cell membrane. In particular, they found that the cell membrane is not uniform in its composition, moreover - asymmetric and filled with liquid. In addition, cells are in constant motion. And the notorious proteins that are part of the cell membrane have different buildings and functions.

Properties and features of the cell membrane

Now let's analyze which functions the cell membrane performs:

The barrier function of the cell membrane - the membrane as the most real border guard, stands on the guard of the cage borders, delaying, not missing harmful or simply inappropriate molecules

The transport function of the cell membrane - the membrane is not only a borderer at the gate of the cell, but also a kind of customs bandwidth, through it the exchange of useful substances with other cells and the environment.

The matrix function is precisely the cell membrane determines the location relative to each other, regulates the interaction between them.

The mechanical function is responsible for limiting one cell from another and in parallel with the correct cell connection with each other, for the formation of them into a homogeneous fabric.

The protective function of the cell membrane is the basis for the construction of the cell's protective shield. In nature, an example of this feature can be solid wood, dense skin, protective shell y, all this thanks to the protective function of the membrane.

Enzymatic function - another important function carried out by some cell proteins. For example, thanks to this function in the intestinal epithelium, the synthesis of digestive enzymes occurs.

Also, in addition to all this, a cellular exchange is carried out through the cell membrane, which can be held in three different reactions:

• Phagocytosis is a cellular exchange in which the phagocyte cells built into the membrane are captured and digested by various nutrients.
• Pinocytosis is a process of capturing a membrane of a cell, contacting the liquid molecules. To do this, on the surface of the membrane, special amplifies are formed, which seem to surround a drop of fluid, forming a bubble, which subsequently "swallows" the membrane.
• Exocytosis is a reverse process when the cell through the membrane highlights the secretory functional fluid to the surface.

The structure of the cell membrane

The cell membrane has lipids of three classes:

• phospholipids (a combination of fats and phosphorus is presented),
• glycolipids (represent a combination of fats and carbohydrates),
• cholesterol.

Phospholipids and glycolipids, in turn, consist of a hydrophilic head, into which two long hydrophobic tails depart. Cholesterol also occupies the space between these tails, not allowing them to bend, all this in some cases makes the membrane of certain cells very tight. In addition to all this, cholesterol molecules are ordered by the structure of the cell membrane.

But be that as it may, and the most important part of the structure of the cell membrane is protein, or rather different proteins that play various important roles. Despite the variety of proteins contained in the membrane there is something that they are united - annular lipids are arranged around all proteins of the membrane. Annular lipids are special structured fats that serve as a kind of protective sheath for proteins, without which they would simply do not work.

The structure of the cell membrane has three layers: the base of the cell membrane is a uniform liquid bilipid layer. Proteins cover it on both sides like a mosaic. It is proteins that, in addition to the functions described above, also play the role of peculiar channels, for which substances are passing through the membrane, unable to penetrate the liquid layer of the membrane. These include, for example, potassium and sodium ions, for their penetration through the membrane, special ion channels of cell membranes are provided. In other words, proteins ensure the permeability of cell membranes.

If you look at the cell membrane through the microscope, we will see a lipid layer formed by small spherical molecules on which they float like the sea proteins. Now you know which substances are included in the cell membrane.

Cell membrane, video

And at the end of the educational video about the cell membrane.

Short description:

Sazonov V.F. 1_1 The structure of the cell membrane [Electronic resource] // Kinesiologist, 2009-2018: [Site]. Renewal date: 02/06/2018 ..__. 201_). _Ocline the structure and functioning of the cell membrane (synonyms: plasmalama, plasmolm, biomembrane, cell shell, outer cell shell, cell membrane, cytoplasmic membrane). These initial information is needed both for cytology and to understand the processes of nervous activity: nervous excitement, braking, synapses and sensory receptors.

Cell membrane (plasma butlemma or plasma aboutlemma)

Definition of concept

Cell membrane (synonyms: plasmalamic, plasmolm, cytoplasmic membrane, biomembrane) is a triple lipoprotein (ie, "zhiro-protein") shell separating the cell from the environment and performing controlled exchange and communication between the cell and the environment surrounding it.

The main thing in this definition is not that the membrane separates the cell from the environment, but just that it connect cell with an environment. Membrane is active cell structure, it constantly works.

The biological membrane is an ultra-thin bimolecular film of phospholipids, inlaid proteins and polysaccharides. This cell structure underlies the barrier, mechanical and matrix properties of a living organism (Antonov V.F., 1996).

Digital view of the membrane

To me, the cell membrane is in the form of a lattice fence with a multitude of doors in it, which surrounds a certain territory. Every small livingitude can through this fence freely move there and back. But larger visitors can only enter the doors, and not all sorts. From different visitors, the keys are only from their doors, and they can not pass through the doors through the doors. So through this fence is constantly going through the flow of visitors and back, because the main function of the membrane-fence is double: separating the territory from the surrounding space and at the same time connect it with the surrounding space. For this, there is a set of holes and doors in the fence - !

Properties of membrane

1. Permeability.

2. Semi-perception (partial permeability).

3. Selective (synonym: selective) permeability.

4. Active permeability (synonym: active transport).

5. Managed permeability.

As we see, the main property of the membrane is its permeability towards various substances.

6. Phagocytoc and pinocytosis.

7. Exocciosis.

8. The presence of electrical and chemical potentials, or rather the potential difference between the inner and outer sides of the membrane. Figuratively can be said that "The membrane turns the cell into the" Electrical Battery "using ion streams management". Details: .

9. Changes in electrical and chemical potential.

10. irritability. Special molecular receptors that are on the membrane can be connected to the signaling (control) substances, as a result of which the state of the membrane and the entire cell can vary. Molecular receptors launch biochemical reactions in response to a connection with ligands (control substances). It is important to note that the signal affects the receptor outside, and the changes continue inside the cell. It turns out that the membrane transmitted information from the environment to the inner medium of the cell.

11. Catalytic enzymatic activity. Enzymes can be built into the membrane or are associated with its surface (both inside and outside the cell), and there they carry out their enzymatic activity.

12. Changing the surface shape and its area. This allows the membrane to form outwards outside or, on the contrary, piercing inside the cell.

13. The ability to form contacts with other cell membranes.

14. Adhesion - the ability to adhere to solid surfaces.

Brief list of membrane properties

• Permeability.
• Endocytosis, exocytosis, transcitosis.
• Potentials.
• Irritability.
• Enzyme activity.
• Contacts.
• Adhesion.

Membrane functions

1. Incomplete insulation of internal contents from the external environment.

2. The main thing in the work of the cell membrane is exchange various substances between the cell and the intercellular medium. This is the property of the membrane as permeability. In addition, the membrane regulates this exchange due to the fact that regulates its permeability.

3. Another important membrane function - creating a difference in chemical and electrical potentials Between its inner and outdoor sides. Due to this, the cell has a negative electric potential.

4. Through the membrane is also carried out information exchange Between the cell and the environment surrounding it. Special molecular receptors located on the membrane may contact control substances (hormones, mediators, modulators) and run biochemical reactions in a cell, leading to various changes in cell operation or in its structures.

Video:The structure of the cell membrane

Video track:Details about the structure of the membrane and transport

Structure of membrane

Cell membrane has a universal three-layer structure. Its among the fatty layer is solid, and the upper and lower protein layers cover it in the form of a mosaic of individual protein areas. The fat layer is the basis that provides the extraction of the environment from the environment, isolating it from the environment. By itself, he is very poorly transmitting water-soluble substances, but it easily misses fat-soluble. Therefore, the permeability of the membrane for water-soluble substances (for example, ions) has to be provided with special protein structures - and.

Below are micrographs of real cell membranes of contact cells obtained using an electron microscope, as well as a schematic pattern, showing the three-layerness of the membrane and the mosaic of its protein layers. To enlarge the image, click on it.

A separate image of an internal lipid (fat) layer of the cell membrane, permeated by integral integrated proteins. The upper and lower protein layers are removed in order not to interfere with the consideration of the lipid double layer.

Figure above: An incomplete schematic representation of the cell membrane (cell shell) shown in Wikipedia.

Please note that the outer and inner protein layers here from the membrane are removed so that we are better visible to the central adhesive double lipid layer. In the real cell membrane from above and below the fatty film (small balls in the figure) float large protein "islands", and the membrane turns out thicker, three-layer: squirrel . So she actually looks like a sandwich of two protein "slices of bread" with a fatty layer of "oil" in the middle, i.e. It has a three-layer structure, not a two-layer.

In this figure, small blue and white balls correspond to hydrophilic (wetting) "heads" of lipids, and the "strings" attached to them - hydrophobic (unmatched) "tails". The proteins are shown only by integrated through membrane proteins (red globules and yellow spirals). Yellow oval points inside the membrane are cholesterol molecules yellow-green chains of beads on the outside of the membrane - chains of oligosaccharides forming glycocalix. Glycocalix is \u200b\u200bas if carbohydrate ("sugar") "gun" on the membrane formed by long carbohydrate-protein molecules sticking out of it.

Live is a small "protein-fat bag" filled with semi-liquid jelly-like content, which is permeated with films and tubes.

The walls of this bag are formed by a double fat (lipid) film, stuck from the inside and outside proteins - cell membrane. Therefore, they say that the membrane has three-layer structure : protein proteins. The cells also have many similar fat membranes that divide its internal space on the compartments. The same membranes are surrounded by cellular organelles: kernel, mitochondria, chloroplasts. So the membrane is a universal molecular structure inherent in all cells and all living organisms.

On the left - no longer real, and the artificial model is a piece of biological membrane: this is an instant image of a fat phospholipid bilayer (that is, a double layer) in the process of its molecular dynamic modeling. The calculated model of the model is shown - 96 Molecules FC ( f.osfatidel h.oline) and 2304 water molecules, only 20544 atoms.

On the right is a visual model of a single molecule of the same lipid, from which the membrane lipid bilayer is collected. At the top he has a hydrophilic (water-loving) head, and below - two hydrophobic (fearing water) of the tail. This lipid has a simple name: 1-steroil-2-docosahexaenoyl-SN-Glycera-3-phosphatidylcholine (18: 0/22: 6 (N-3) CIS FX), but you do not need to remember it if you are not Planning to bring your teacher to fainting the depth of your knowledge.

You can give a more accurate scientific definition of the cell:

- It is a limited active membrane, an ordered, structured inhomogeneous system of biopolymers involved in a unified combination of exchange, energy and information processes, and also carrying out maintenance and reproduction of the entire system as a whole.

Inside the cell is also permeated with membranes, and there is not water between the membranes, but a viscous gel / solid density. Therefore, the interacting molecules in the cell do not float freely, as in a test tube with an aqueous solution, and mainly sit (immobilized) on polymer structures of the cytoskeleton or intracellular membranes. And chemical reactions therefore pass inside the cell almost as in the solid, and not in the liquid. The outer membrane surrounding the cell is also rushed with enzymes and molecular receptors, which makes it a very active part of the cell.

The cell membrane (plasma, plasmolm) is an active shell separating the environment from the environment and connecting it with the environment. © Sazonov V.F., 2016.

From this determination of the membrane it follows that it does not just limit the cell, and actively workingBy tying it with its environment.

Fat from which the membranes are special, so his molecules are not called not just fat, but "Lipids", "phospholipids", "Sphingolipid". The membrane film is double, i.e. it consists of two players who merged with each other. Therefore, the textbooks write that the base of the cell membrane consists of two lipid layers (or from " bISOTEY.", i.e. double layer). In each individual lipid layer, one side can be saved with water, and the other can not. So, these film sticks stick together with each other with their unparalleled parties.

Membrane bacteria

The shell of the prokaryotic cell of gram-negative bacteria consists of several layers shown in the figure below.
Layers of the shell gram-negative bacteria:
1. Inner three-layer cytoplasmic membrane, which comes into contact with cytoplasm.
2. Cell wall, which consists of Minein.
3. The outer three-layer cytoplasmic membrane, which has the same lipid system with protein complexes, like the inner membrane.
Communication of gram-negative bacterial cells with an external world through such a complex three-step structure does not give them advantages in survival in severe conditions compared with gram-positive bacteria that have a less powerful shell. They are just as poorly carry high temperatures, increased acidity and pressure drops.

Video track: Plasma membrane. E.V. Cheval, K.B.

Video track: Membrane as a cell border. A. Ilyaskin

The importance of the ion channels of the membrane

It is easy to understand that only fat-soluble substances can penetrate through the membrane fatty film. These are fats, alcohols, gases. For example, in red blood cells, right through the membrane easily pass inside and outward oxygen and carbon dioxide. But water and water-soluble substances (for example, ions) are simply so through the membrane can not go inside any cell. This means that they need special holes for them. But if you just make a hole in a fatty film, then it will immediately delay back. What to do? The output in nature was found: it is necessary to make special protein transport structures and stretch them through the membrane. This is exactly what channels are obtained for transmitting non-dissolishable substances - ionic cells of the cell membrane.

So, to give its membrane additional properties of permeability for polar molecules (ions and water) cells synthesize special proteins in the cytoplasm, which are then embedded in the membrane. They are two types: proteins-conveyors (for example, transport ATPases) and proteins-channel fermers (channels of channels). These proteins are embedded in a double fat layer of the membrane and form transport structures in the form of conveyors or as ion channels. Through these transport structures, various water soluble substances can now be held, which can not be through a fat membrane film.

In general, the proteins built into the membrane are also called integral, It is because they seem to be included in the membrane and permeate it through. Other proteins, not integral, form the islands, "floating" on the surface of the membrane: either by its outer surface, or internal. After all, everyone knows that fat is good lubricant and slide it is easy!

conclusions

1. In general, the membrane is three-layer:

1) outer layer of protein "islands",

2) Fat two-layer "Sea" (lipid bilay), i.e. Double Lipid Film,

3) the inner layer of protein "islands".

But there is still a loose outer layer - glycocalix, which form glycoproteins sticking out of the membrane. They are molecular receptors with which signal control stuffs are associated.

2. Special protein structures are embedded in the membrane, providing its site for ions or other substances. No need to forget that in some places the fatty sea is permeated with integral proteins through. And it is the integral proteins that form special transport structures cell membrane (see section 1_2 Membrane Transport Mechanisms). Through them, substances fall inside the cells, and also output from the cell.

3. From any side of the membrane (outer and internal), as well as inside the membrane, proteins-enzymes may be located, which affect the state of the membrane itself and on the life of the entire cell.

So the cell membrane is an active changing structure that works actively in the interests of the entire cell and connects it to the outside world, and not just a "protective shell". This is the most important thing that you need to know about the cell membrane.

In medicine, membrane proteins are often used as a "target" for medicines. Receptors, ion channels, enzymes, transport systems are as such tarches. Recently, in addition to the membrane, the target for medicinal substances also become genes hidden in the cellular core.

Video:Introduction to the biophysics of the cell membrane: membrane structure 1 (Vladimirov Yu.A.)

Video:History, structure and functions of the cell membrane: Membrane structure 2 (Vladimirov Yu.A.)

© 2010-2018 Sazonov V.F., © 2010-2016 Kineziolog.Bodhy.

The main structural unit of a living organism is a cell, which is a differentiated section of the cytoplasm, surrounded by a cell membrane. Due to the fact that the cell performs many essential functions, such as reproduction, power, movement, the shell must be plastic and dense.

The history of the discovery and research of the cell membrane

In 1925, a successful experiment was raised by Grendel and Gorder to identify "shadows" of red blood cells, or empty shells. Despite several structural mistakes, scientists were discovered by lipid bilayer. Their works continued Danielli, Dawson in 1935, Robertson in 1960. As a result of many years of work and accumulation of arguments in 1972, Singer and Nicholson created a liquid-mosaic model of the structure of the membrane. Further experiments and research confirmed the works of scientists.

Value

What is the cell membrane? This word began to be used over a hundred years ago, in translation from Latin, it means "film", "skin". So denote the boundary of the cell, which is a natural barrier between the internal content and the external environment. The structure of the cell membrane implies half perception, due to which moisture and nutrients and decay products can freely pass through it. This shell can be called the main structural component of the organization of the cell.

Consider the main functions of the cell membrane

1. Separate the internal content of the cell and the components of the external environment.

2. It helps to maintain the permanent chemical composition of the cell.

3. Adjusts the correct metabolism.

4. Provides the relationship between cells.

5. Recognizes signals.

6. Protection function.

"Plasma Shell"

The outer cell membrane, also called plasma, is an ultramicroscopic film whose thickness ranges from five to seven nanomillimeters. It consists mainly of protein compounds, phospholides, water. The film is elastic, easily absorbs water, and also rapidly restores its integrity after damage.

Different with a universal structure. This membrane occupies a border position, participates in the process of electoral permeability, the removal of decay products, synthesizes them. The relationship with the "neighbors" and the reliable protection of the internal content from damage makes it an important component in such a matter as the structure of the cell. The cell membrane of animal organisms is sometimes covered with the finest layer - glycocalix, which includes proteins and polysaccharides. The plant cells outside the membrane are protected by a cell wall that performs the function of the support and maintaining the form. The main component of its composition is a fiber (cellulose) - polysaccharide, not soluble in water.

Thus, the outer cell membrane performs the function of restoration, protection and interaction with other cells.

The structure of the cell membrane

The thickness of this movable shell varies from six to ten nanomillimeters. Cell membrane cells has a special composition, the basis of which serves as a lipid bilayer. Hydrophobic tails, inert to water, are placed on the inside, while hydrophilic heads interacting with water are turned out. Each lipid represents phospholipid, which is the result of the interaction of substances such as glycerin and sphingosin. Lipid frameworks closely surround the proteins that are located a lack of layer. Some of them are shipped in a lipid layer, the rest are passing through it. As a result, the sections permeable for water are formed. The functions performed by these proteins are different. Some of them are enzymes, the rest are transported proteins that carry various substances from the external environment on the cytoplasm and back.

The cell membrane through permeated and closely linked by integral proteins, and with peripheral communication less durable. These proteins perform an important function that consists in maintaining the structure of the membrane, obtaining and converting signals from the environment, the transport of substances, the catalysis of the reactions that occur on the membranes.

Structure

The base of the cell membrane is a bimolecular layer. Due to its continuity, the cell has barrier and mechanical properties. At different stages of life, this bilay can break. As a result, structural defects of through hydrophilic pores are formed. In this case, absolutely all functions of such a component as a cell membrane may vary. The kernel may suffer from external influences.

Properties

Cell membrane cells have interesting features. Due to the yield, this shell is not a rigid structure, and the main part of proteins and lipids, which are included in its composition, is fluent in the plane of the membrane.

In general, the cell membrane is asymmetric, therefore the composition of protein and lipid layers differs. Plasma Mammbians in animal cells from their outer side have a glycoprotein layer, which performs receptor and signaling functions, and also plays a large role in the process of combining cells into the fabric. The cell membrane is polar, that is, on the outside, the charge is positive, and from the inside - negative. In addition to the listed, the cell shell has election insight.

This means that, in addition to water, only a certain group of molecules and ions of the soluble substances is passed into the cell. The concentration of such a substance as sodium, in most cells is significantly lower than in the external environment. For potassium ions, another ratio is characterized by another ratio: their number in the cell is much higher than in the environment. In connection with these sodium ions, the desire to penetrate into the cellular shell is inherent, and potassium ions seek to free themselves. Under these circumstances, the membrane activates a special system that performs a "pumping" role, equalizing the concentration of substances: sodium ions are pumped out on the surface of the cell, and potassium ions are pumped inside. This feature is included in the most important functions of the cell membrane.

A similar desire of sodium ions and potassium moves inside from the surface plays a big role in the issue of transportation of sugar and amino acids in the cage. In the process of active removal of sodium ions from the membrane cell, conditions create conditions for new glucose receipts and amino acids inward. On the contrary, in the process of transporting potassium ions inside the cell replenishes the number of "transporters" of the decay products from the inside of cells into the outer environment.

How does the cell power occur through the cell membrane?

Many cells absorb substances through such processes as phagocytosis and pinocytosis. With a first embodiment, a flexible outer membrane creates a small recess in which the particle is captured. Then the deepening diameter becomes greater than the surrounded particle falls into the cell cytoplasm. Through phagocytosis, some simplest, for example, amids, as well as blood tales - leukocytes and phagocytes are fed. Similarly, the cells are absorbed by the liquid that contains the necessary useful substances. This believes is called pinocytosis.

The outer membrane is closely connected to the endoplasmic cell network.

Many types of the main components of the tissue on the surface of the membrane are protrusions, folds, microvilles. Vegetable cells outside this shell are covered with another, thick and distinctly distinguishable in the microscope. The fiber, from which they consist, helps to form a support of vegetable tissues, such as wood. Animal cells also have a number of external structures that are on top of the cell membrane. They are exceptionally defensive, an example of this is a chitin contained in insect covered cells.

In addition to cellular, there is an intracellular membrane. Its function is to divide the cell into several specialized closed compartments - compartments or organelles, where a certain environment should be maintained.

Thus, it is impossible to overestimate the role of such a component of the main unit of a living organism, like a cell membrane. The structure and functions involve a significant expansion of the total cell surface area, improvement of metabolic processes. This molecular structure includes proteins and lipids. Separating the cell from the external environment, the membrane ensures its integrity. With its help, the intercellular communications are supported on a sufficiently strong level forming fabrics. In this regard, we can conclude that the cell membrane plays one of the most important roles in the cage. The structure and functions performed by it are radically different in various cells, depending on their purpose. Through these features, the variety of physiological activity of cell membranes and their roles in the existence of cells and tissues is achieved.

Universal biological membrane Formed by a double layer of phospholipid molecules with a total thickness of 6 microns. At the same time, the hydrophobic tails of phospholipid molecules are addressed inside, towards each other, and the polar hydrophilic heads are overlooking the membrane, towards water. Lipids provide the main physicochemical properties of membranes, in particular, their fluidity at body temperature. Squels are built into this double lipid layer.

They are divided by integral (permeate the whole bilayer lipids), semi-integrated (penetrate to half of the lipid bilayer), or the rotors (located on the inner or outer surface of the lipid bilayer).

At the same time, protein molecules are located in a lipid bisal mosaic and can "swim" in the "Lipid Sea" like the icebergs, due to the membranes of membranes. In its function, these proteins can be structural(maintain a certain membrane structure), receptor (to form biologically active receptors), transport (carry out transport substances through the membrane) and fermented (catalyze certain chemical reactions). This most recognized currently liquid-mosaic model The biological membrane was proposed in 1972 Singer and Nikolson.

The membranes are performed in the cell a distinction function. They divide the cell on the compartments, compartments in which the processes and chemical reactions can go independently of each other. For example, aggressive hydrolytic enzymes with lysosomes capable of splitting most of the organic molecules are separated from the remaining cytoplasm with the help of membranes. In the event of its destruction, self-sizing and cell death occurs.

Having a general structure of the structure, different biological membranes of cells differ in their chemical composition, organization and properties, depending on the functions of the structures that they form.

Plasma membrane, structure, functions.

The cytlem is a biological membrane surrounding the cell outside. This is the fatal (10 nm) and the organized cell membrane is complex. It is based on a universal biological membrane covered outside glycocalix, and from the inside, from the side of the cytoplasm, submembered layer (Fig.2-1B). Glycocalix (3-4 nm thickness) is represented by outer, carbohydrate areas of complex proteins - glycoproteins and glycolipids that are part of the membrane. These carbohydrate chains play the role of receptors that provide recognition by the cell of neighboring cells and the intercellular substance and interact with them. This layer also includes surface and semi-integrated proteins, the functional sections of which are in the above-handed zone (for example, immunoglobulins). Glycicalce contains histocompatibility receptors, receptors of many hormones and neurotransmitters.

Submembered, cortical layer Formed by microtubes, microfibrilles and reduced microfilaments, which are part of the cell cytoskeleton. The subable layer ensures that the cell form is maintained, the creation of its elasticity provides changes in the cell surface. Due to this cell participates in endo and exocytosis, secretion, motion.

Cythemma performs lots of functions:

1) the distinctive (cytlemma separates, degradates the cell from the environment and provides its connection with the external environment);

2) recognition by this cell of other cells and attachment to them;

3) the recognition of the cell of the intercellular substance and the attachment to its elements (fibers, basal membrane);

4) transport of substances and particles in the cytoplasm and from it;

5) Interaction with signal molecules (hormones, mediators, cytokines) due to the presence of specific receptors on its surface;

1. provides the motion of the cell (formation of pseudopodies) due to the connection of the cytlemma with the reduced elements of the cytoskeleton.

In the cytlemma there are numerous receptorsthrough which biologically active substances ( ligands, signal molecules, first intermediaries: Hormones, mediators, growth factors) act on the cell. Receptors are genetically deterministic macromolecular sensors (proteins, glyco- and lipoproteins) built into the cytolemma or located inside the cell and specialized in the perception of specific signals of chemical or physical nature. Biologically active substances when interacting with the receptor cause a cascade of biochemical changes in a cell, transforming into a specific physiological response (change in the function of the cell).

All receptors have a common structure of the structure and consist of three parts: 1) a premissal interaction with a substance (ligand); 2) intrambled signal transfers and 3) intracellular immersed in cytoplasm.

Types of intercellular contacts.

The cytlemis is also involved in the formation of special structures - intercellular connections, contactswhich provide close interaction between nearby cells. Distinguish simple and sophisticated Intercellular connections. IN simple Intercellular compounds of cell cytlemis come closer to a distance of 15-20 nm and their glycocalx molecules interact with each other (Fig. 2-3). Sometimes the protrusion of the cytolemma of one cell enters into the deepening of the neighboring cell, forming gear and finger connections (connections "by type of lock").

Sophisticated Intercellular compounds are several types: locking, clutching and communication (Fig. 2-3). TO lockingconnections are referred tight contactor locking zone. In this case, the integral proteins of the glycocalcalex of neighboring cells form the similarity of the cellular network around the perimeter of adjacent epithelial cells in their apical parts. Due to this, the intercellular gaps are locked, eliminate from the external environment (Fig. 2-3).

Fig. 2-3. Different types of intercellular connections.

1. Simple connection.
2. Dense connection.
3. Adhesive belt.
4. Desmosomom.
5. Semi-mosmom.
6. Slotovoe (communication) connection.
7. Microvili.

(According to Yu. I. Afanasyev, N. A. Yurina).

TO couplingbinding compounds include adhesive subtle and desremes. Adhesive belt Located around the apical parts of the cells of the single-layer epithelium. In this zone, the integral glycoproteins of the glycocalcalis of neighboring cells interact with each other, and to them from the cytoplasm, subable proteins are suitable, including beams of actin microfilaments. Desmosomomomomas (clutch stains) - Paired structures of about 0.5 microns in size. In them, the glycoproteins of the citolem of neighboring cells are closely interacting, and from the cells of the cells in these areas in the cytlemma, the beams of intermediate filaments of the cell cytosethelet are woven (Fig. 2-3).

TO communication compounds include slim-like compounds (Nexuss) and synapses. Nexus They have a size of 0.5-3 microns. In them, the cytlemmas of neighboring cells come closer to 2-3 nm and have numerous ion channels. Through them, ions can move from one cell to another, transmitting excitation, for example, between myocardial cells. Sinapsy Characteristic for nervous tissue and occur between nerve cells, as well as between nervous and effector cells (muscle, glazed). They have a synaptic slit, where, when passing the nerve pulse from the presynaptic part of the synapse, a neurotiator is ejected, transmitting a nervous pulse to another cell (see Read more. In the chapter "Nervous Fabric").

It has a thickness of 8-12 nm, so it is impossible to consider it in a light microscope. The structure of the membrane is studied using an electron microscope.

The plasma membrane is formed by two layers of lipid - bilipid layer, or bilayer. Each molecule consists of a hydrophilic head and a hydrophobic tail, and in the biological membranes of lipids are located outside, tails inside.

Numerous protein molecules are immersed in the bilipid layer. Some of them are on the surface of the membrane (external or internal), others permeate the membrane.

Functions of plasma membrane

The membrane protects the contents of the cell from damage, maintains the shape of the cell, selectively skips the necessary substances inside the cell and displays the exchange products, and also provides cellular communication.

The barrier, the fertile function of the membrane provides a double layer of lipids. It does not give the contents of the cell spread, mix with the environment or intercellular fluid, and prevents hazardous substances into the cell.

A number of essential functions of the cytoplasmic membrane are carried out at the expense of proteins immersed in it. Using protein receptors can perceive various irritations on its surface. Transport proteins form the finest channels through which potassium, calcium ions, and other small-diameter ions pass inside the cells. Proteins - provide life processes in the most.

Large food particles that are not capable of passing through thin membrane channels enter the cells by phagocytosis or pinocytosis. The general name of these processes is endocytosis.

How does endocytosis occurs - the penetration of large food particles into the cage

The food particle comes into contact with the outer membrane of the cell, and in this place is formed in the fusion. Then the particle, surrounded by the membrane, falls inside the cell, is formed digestive, and digestive enzymes penetrate inside the resulting bubble.

Blood leukocytes that can capture and digest foreign bacteria are called phagocytes.

In the case of pinocytosis, no solid particles are captured in the pinocytosis, but the liquid droplets with substances dissolved in it. This mechanism is one of the main pathways of penetration of substances into the cell.

Plant cells coated on top of the membrane with a solid layer of the cell wall are not capable of phagocytosis.

The process, inverse endocytosis, - exocytosis. Synthesized substances (for example, hormones) are packaged into membrane bubbles, suitable to, embedded in it, and the contents of the bubble is ejected from the cell. Thus, the cell can get rid of unnecessary exchange products.