The role of the cell membrane in the cell. The most important conclusions about the structure and functions of cell membranes

Delimitative ( barrier) - separate cellular contents from the external environment;

Regulate the exchange between the cell and the environment;

They divide cells into compartments, or compartments, intended for certain specialized metabolic pathways ( dividing);

It is the site of some chemical reactions (light reactions of photosynthesis in chloroplasts, oxidative phosphorylation during respiration in mitochondria);

Provide communication between cells in the tissues of multicellular organisms;

Transport- carries out transmembrane transport.

Receptor- are the location of receptor sites that recognize external stimuli.

Transport of substances through the membrane - one of the leading functions of the membrane, ensuring the exchange of substances between the cell and the external environment. Depending on the energy consumption for the transfer of substances, they are distinguished:

passive transport, or facilitated diffusion;

active (selective) transport with the participation of ATP and enzymes.

transport in membrane packaging. There are endocytosis (into the cell) and exocytosis (out of the cell) - mechanisms that transport large particles and macromolecules through the membrane. During endocytosis, the plasma membrane forms an invagination, its edges merge, and a vesicle is released into the cytoplasm. The vesicle is delimited from the cytoplasm by a single membrane, which is part of the outer cytoplasmic membrane. There are phagocytosis and pinocytosis. Phagocytosis is the absorption of large particles that are quite hard. For example, phagocytosis of lymphocytes, protozoa, etc. Pinocytosis is the process of capturing and absorbing droplets of liquid with substances dissolved in it.

Exocytosis is the process of removing various substances from the cell. During exocytosis, the membrane of the vesicle, or vacuole, fuses with the outer cytoplasmic membrane. The contents of the vesicle are removed beyond the cell surface, and the membrane is included in the outer cytoplasmic membrane.

At the core passive transport of uncharged molecules lies in the difference between the concentrations of hydrogen and charges, i.e. electrochemical gradient. Substances will move from an area with a higher gradient to an area with a lower one. The speed of transport depends on the difference in gradients.

Simple diffusion is the transport of substances directly through the lipid bilayer. Characteristic of gases, non-polar or small uncharged polar molecules, soluble in fats. Water quickly penetrates the bilayer because its molecule is small and electrically neutral. The diffusion of water through membranes is called osmosis.

Diffusion through membrane channels is the transport of charged molecules and ions (Na, K, Ca, Cl) penetrating through the membrane due to the presence of special channel-forming proteins that form water pores.

Facilitated diffusion is the transport of substances using special transport proteins. Each protein is responsible for a strictly defined molecule or group of related molecules, interacts with it and moves through the membrane. For example, sugars, amino acids, nucleotides and other polar molecules.

Active transport carried out by carrier proteins (ATPase) against an electrochemical gradient, with energy consumption. Its source is ATP molecules. For example, sodium is a potassium pump.

The concentration of potassium inside the cell is much higher than outside it, and sodium - vice versa. Therefore, potassium and sodium cations passively diffuse through the water pores of the membrane along a concentration gradient. This is explained by the fact that the permeability of the membrane for potassium ions is higher than for sodium ions. Accordingly, potassium diffuses out of the cell faster than sodium into the cell. However, for normal cell functioning a certain ratio of 3 potassium and 2 sodium ions is necessary. Therefore, there is a sodium-potassium pump in the membrane that actively pumps sodium out of the cell and potassium into the cell. This pump is a transmembrane membrane protein capable of conformational rearrangements. Therefore, it can attach to itself both potassium and sodium ions (antiport). The process is energy intensive:

From the inside of the membrane, sodium ions and an ATP molecule enter the pump protein, and potassium ions come from the outside.

Sodium ions combine with a protein molecule, and the protein acquires ATPase activity, i.e. the ability to cause ATP hydrolysis, which is accompanied by the release of energy that drives the pump.

The phosphate released during ATP hydrolysis attaches to the protein, i.e. phosphorylates the protein.

Phosphorylation causes conformational changes in the protein; it becomes unable to retain sodium ions. They are released and move outside the cell.

The new conformation of the protein promotes the attachment of potassium ions to it.

The addition of potassium ions causes dephosphorylation of the protein. It changes its conformation again.

A change in protein conformation leads to the release of potassium ions inside the cell.

The protein is again ready to attach sodium ions to itself.

In one cycle of operation, the pump pumps out 3 sodium ions from the cell and pumps in 2 potassium ions.

Cytoplasm– an obligatory component of the cell, located between the surface apparatus of the cell and the nucleus. This is a complex heterogeneous structural complex consisting of:

hyaloplasma

organelles (permanent components of the cytoplasm)

inclusions are temporary components of the cytoplasm.

Cytoplasmic matrix(hyaloplasm) is the internal contents of the cell - a colorless, thick and transparent colloidal solution. The components of the cytoplasmic matrix carry out biosynthetic processes in the cell and contain enzymes necessary for energy production, mainly due to anaerobic glycolysis.

Basic properties of the cytoplasmic matrix.

Determines the colloidal properties of the cell. Together with the intracellular membranes of the vacuolar system, it can be considered a highly heterogeneous or multiphase colloidal system.

Provides a change in the viscosity of the cytoplasm, a transition from a gel (thicker) to a sol (more liquid), which occurs under the influence of external and internal factors.

Provides cyclosis, amoeboid movement, cell division and movement of pigment in chromatophores.

Determines the polarity of the location of intracellular components.

Provides mechanical properties of cells - elasticity, ability to merge, rigidity.

Organelles– permanent cellular structures that ensure the cell performs specific functions. Depending on the structural features, there are:

membrane organelles - have a membrane structure. They can be single-membrane (ER, Golgi apparatus, lysosomes, vacuoles of plant cells). Double-membrane (mitochondria, plastids, nucleus).

Non-membrane organelles - do not have a membrane structure (chromosomes, ribosomes, cell center, cytoskeleton).

General-purpose organelles are characteristic of all cells: nucleus, mitochondria, cell center, Golgi apparatus, ribosomes, EPS, lysosomes. When organelles are characteristic of certain cell types, they are called specialty organelles (for example, myofibrils that contract a muscle fiber).

Endoplasmic reticulum- a single continuous structure, the membrane of which forms many invaginations and folds that look like tubules, microvacuoles and large cisterns. The ER membranes are, on the one hand, connected to the cell cytoplasmic membrane, and on the other, to the outer shell of the nuclear membrane.

There are two types of EPS - rough and smooth.

In rough or granular ER, cisterns and tubules are associated with ribosomes. is the outer side of the membrane. Smooth or agranular ER has no connection with ribosomes. This is the inner side of the membrane.

The cell membrane is the structure that covers the outside of the cell. It is also called cytolemma or plasmalemma.

This formation is built from a bilipid layer (bilayer) with proteins built into it. The carbohydrates that make up the plasmalemma are in a bound state.

The distribution of the main components of the plasmalemma is as follows: more than half of the chemical composition is proteins, a quarter is occupied by phospholipids, and a tenth is cholesterol.

Cell membrane and its types

The cell membrane is a thin film, the basis of which is made up of layers of lipoproteins and proteins.

According to localization, membrane organelles are distinguished, which have some features in plant and animal cells:

mitochondria;
core;
endoplasmic reticulum;
Golgi complex;
lysosomes;
chloroplasts (in plant cells).

There is also an inner and outer (plasmolemma) cell membrane.

Structure of the cell membrane

The cell membrane contains carbohydrates that cover it in the form of a glycocalyx. This is a supra-membrane structure that performs a barrier function. The proteins located here are in a free state. Unbound proteins participate in enzymatic reactions, providing extracellular breakdown of substances.

Proteins of the cytoplasmic membrane are represented by glycoproteins. Based on their chemical composition, proteins that are completely included in the lipid layer (along its entire length) are classified as integral proteins. Also peripheral, not reaching one of the surfaces of the plasmalemma.

The former function as receptors, binding to neurotransmitters, hormones and other substances. Insertion proteins are necessary for the construction of ion channels through which the transport of ions and hydrophilic substrates occurs. The latter are enzymes that catalyze intracellular reactions.

Basic properties of the plasma membrane

The lipid bilayer prevents the penetration of water. Lipids are hydrophobic compounds represented in the cell by phospholipids. The phosphate group faces outward and consists of two layers: the outer one, directed to the extracellular environment, and the inner one, delimiting the intracellular contents.

Water-soluble areas are called hydrophilic heads. The fatty acid sites are directed into the cell, in the form of hydrophobic tails. The hydrophobic part interacts with neighboring lipids, which ensures their attachment to each other. The double layer has selective permeability in different areas.

So, in the middle the membrane is impermeable to glucose and urea; hydrophobic substances pass through here freely: carbon dioxide, oxygen, alcohol. Cholesterol is important; the content of the latter determines the viscosity of the plasmalemma.

Functions of the outer cell membrane

The characteristics of the functions are briefly listed in the table:

Membrane function	Description
Barrier role	The plasmalemma performs a protective function, protecting the contents of the cell from the effects of foreign agents. Thanks to the special organization of proteins, lipids, and carbohydrates, the semipermeability of the plasmalemma is ensured.
Receptor function	Biologically active substances are activated through the cell membrane in the process of binding to receptors. Thus, immune reactions are mediated through the recognition of foreign agents by the cell receptor apparatus localized on the cell membrane.
Transport function	The presence of pores in the plasmalemma allows you to regulate the flow of substances into the cell. The transfer process occurs passively (without energy consumption) for compounds with low molecular weight. Active transport is associated with the expenditure of energy released during the breakdown of adenosine triphosphate (ATP). This method takes place for the transfer of organic compounds.
Participation in digestive processes	Substances are deposited on the cell membrane (sorption). Receptors bind to the substrate, moving it into the cell. A bubble is formed, lying freely inside the cell. Merging, such vesicles form lysosomes with hydrolytic enzymes.
Enzymatic function	Enzymes are essential components of intracellular digestion. Reactions requiring the participation of catalysts occur with the participation of enzymes.

What is the importance of the cell membrane

The cell membrane is involved in maintaining homeostasis due to the high selectivity of substances entering and exiting the cell (in biology this is called selective permeability).

Outgrowths of the plasmalemma divide the cell into compartments (compartments) responsible for performing certain functions. Specifically designed membranes corresponding to the fluid-mosaic pattern ensure the integrity of the cell.

Cell membrane- this is the cell membrane that performs the following functions: separation of the contents of the cell and the external environment, selective transport of substances (exchange with the environment external to the cell), the site of some biochemical reactions, the union of cells into tissues and reception.

Cell membranes are divided into plasma (intracellular) and external. The main property of any membrane is semi-permeability, that is, the ability to pass only certain substances. This allows for selective exchange between the cell and the external environment or exchange between cell compartments.

Plasma membranes are lipoprotein structures. Lipids spontaneously form a bilayer (double layer), and membrane proteins “float” in it. The membranes contain several thousand different proteins: structural, transporters, enzymes, etc. Between the protein molecules there are pores through which hydrophilic substances pass (the lipid bilayer prevents their direct penetration into the cell). Glycosyl groups (monosaccharides and polysaccharides) are attached to some molecules on the surface of the membrane, which are involved in the process of cell recognition during tissue formation.

Membranes vary in thickness, usually ranging from 5 to 10 nm. The thickness is determined by the size of the amphiphilic lipid molecule and is 5.3 nm. A further increase in membrane thickness is due to the size of membrane protein complexes. Depending on external conditions (cholesterol is the regulator), the structure of the bilayer can change so that it becomes more dense or liquid - the speed of movement of substances along the membranes depends on this.

Cell membranes include: plasma membrane, karyolemma, membranes of the endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, inclusions, etc.

Lipids are insoluble in water (hydrophobicity), but soluble in organic solvents and fats (lipophilicity). The composition of lipids in different membranes is not the same. For example, the plasma membrane contains a lot of cholesterol. The most common lipids in the membrane are phospholipids (glycerophosphatides), sphingomyelins (sphingolipids), glycolipids and cholesterol.

Phospholipids, sphingomyelins, and glycolipids consist of two functionally different parts: a hydrophobic nonpolar one that carries no charges - “tails” consisting of fatty acids, and a hydrophilic one containing charged polar “heads” - alcohol groups (for example, glycerol).

The hydrophobic part of the molecule usually consists of two fatty acids. One of the acids is saturated, and the second is unsaturated. This determines the ability of lipids to spontaneously form bilayer (bilipid) membrane structures. Membrane lipids perform the following functions: barrier, transport, protein microenvironment, electrical resistance of the membrane.

Membranes differ from each other in their set of protein molecules. Many membrane proteins consist of regions rich in polar (charge-bearing) amino acids and regions with nonpolar amino acids (glycine, alanine, valine, leucine). Such proteins in the lipid layers of membranes are located so that their non-polar sections are, as it were, immersed in the “fat” part of the membrane, where the hydrophobic sections of lipids are located. The polar (hydrophilic) part of these proteins interacts with the lipid heads and faces the aqueous phase.

Biological membranes have common properties:

membranes are closed systems that do not allow the contents of the cell and its compartments to mix. Violation of the integrity of the membrane can lead to cell death;

superficial (planar, lateral) mobility. In membranes there is a continuous movement of substances across the surface;

membrane asymmetry. The structure of the outer and surface layers is chemically, structurally and functionally heterogeneous.

Short description:

Sazonov V.F. 1_1 Structure of the cell membrane [Electronic resource] // Kinesiologist, 2009-2018: [website]. Update date: 02/06/2018..__.201_). _The structure and functioning of the cell membrane is described (synonyms: plasmalemma, plasmalemma, biomembrane, cell membrane, outer cell membrane, cell membrane, cytoplasmic membrane). This initial information is necessary both for cytology and for understanding the processes of nervous activity: nervous excitation, inhibition, the functioning of synapses and sensory receptors.

Cell membrane (plasma) A lemma or plasma O lemma)

Definition of the concept

The cell membrane (synonyms: plasmalemma, plasmalemma, cytoplasmic membrane, biomembrane) is a triple lipoprotein (i.e., “fat-protein”) membrane that separates the cell from the environment and carries out controlled exchange and communication between the cell and its environment.

The main thing in this definition is not that the membrane separates the cell from the environment, but precisely that it connects cell with the environment. The membrane is active the structure of the cell, it is constantly working.

A biological membrane is an ultrathin bimolecular film of phospholipids encrusted with proteins and polysaccharides. This cellular structure underlies the barrier, mechanical and matrix properties of a living organism (Antonov V.F., 1996).

A figurative representation of a membrane

To me, the cell membrane looks like a lattice fence with many doors in it, which surrounds a certain territory. Any small living creature can move freely back and forth through this fence. But larger visitors can only enter through doors, and even then not all doors. Different visitors have keys only to their own doors, and they cannot go through other people's doors. So, through this fence there are constantly flows of visitors back and forth, because the main function of the membrane fence is twofold: to separate the territory from the surrounding space and at the same time connect it with the surrounding space. This is why there are many holes and doors in the fence - !

Membrane properties

1. Permeability.

2. Semi-permeability (partial permeability).

3. Selective (synonym: selective) permeability.

4. Active permeability (synonym: active transport).

5. Controlled permeability.

As you can see, the main property of a membrane is its permeability to various substances.

6. Phagocytosis and pinocytosis.

7. Exocytosis.

8. The presence of electrical and chemical potentials, or rather the potential difference between the inner and outer sides of the membrane. Figuratively we can say that “the membrane turns the cell into an “electric battery” by controlling ionic flows”. Details: .

9. Changes in electrical and chemical potential.

10. Irritability. Special molecular receptors located on the membrane can connect with signaling (control) substances, as a result of which the state of the membrane and the entire cell can change. Molecular receptors trigger biochemical reactions in response to the connection of ligands (control substances) with them. It is important to note that the signaling substance acts on the receptor from the outside, and the changes continue inside the cell. It turns out that the membrane transferred information from the environment to the internal environment of the cell.

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

12. Changing the shape of the surface and its area. This allows the membrane to form outgrowths outward or, conversely, invaginations into the cell.

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

14. Adhesion - the ability to stick to hard surfaces.

Brief list of membrane properties

Permeability.
Endocytosis, exocytosis, transcytosis.
Potentials.
Irritability.
Enzyme activity.
Contacts.
Adhesion.

Membrane functions

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

2. The main thing in the functioning of the cell membrane is exchange various substances between the cell and the intercellular environment. This is due to the membrane property of permeability. In addition, the membrane regulates this exchange by regulating its permeability.

3. Another important function of the membrane is creating a difference in chemical and electrical potentials between its inner and outer sides. Due to this, the inside of the cell has a negative electrical potential - .

4. The membrane also carries out information exchange between the cell and its environment. Special molecular receptors located on the membrane can bind to control substances (hormones, mediators, modulators) and trigger biochemical reactions in the cell, leading to various changes in the functioning of the cell or in its structures.

Video:Cell membrane structure

Video lecture:Details about membrane structure and transport

Membrane structure

The cell membrane has a universal three-layer structure. Its middle fat layer is continuous, and the upper and lower protein layers cover it in the form of a mosaic of separate protein areas. The fat layer is the basis that ensures the isolation of the cell from the environment, isolating it from the environment. By itself, it allows water-soluble substances to pass through very poorly, but easily allows fat-soluble substances to pass through. Therefore, the permeability of the membrane for water-soluble substances (for example, ions) must be ensured by special protein structures - and.

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

A separate image of the inner lipid (fat) layer of the cell membrane, permeated with integral embedded proteins. The top and bottom protein layers have been removed so as not to interfere with viewing the lipid bilayer

Figure above: Partial schematic representation of a cell membrane (cell membrane), given on Wikipedia.

Please note that the outer and inner protein layers have been removed from the membrane here so that we can better see the central fatty lipid bilayer. In a real cell membrane, large protein “islands” float above and below the fatty film (small balls in the figure), and the membrane turns out to be thicker, three-layered: protein-fat-protein . So it's actually like a sandwich of two protein "pieces of bread" with a fatty layer of "butter" in the middle, i.e. has a three-layer structure, not a two-layer one.

In this picture, the small blue and white balls correspond to the hydrophilic (wettable) “heads” of the lipids, and the “strings” attached to them correspond to the hydrophobic (non-wettable) “tails”. Of the proteins, only integral end-to-end membrane proteins (red globules and yellow helices) are shown. The yellow oval dots inside the membrane are cholesterol molecules. The yellow-green chains of beads on the outside of the membrane are chains of oligosaccharides that form the glycocalyx. A glycocalyx is a kind of carbohydrate (“sugar”) “fluff” on a membrane, formed by long carbohydrate-protein molecules sticking out of it.

Living is a small “protein-fat sac” filled with semi-liquid jelly-like contents, which are permeated with films and tubes.

The walls of this sac are formed by a double fatty (lipid) film, covered inside and outside with proteins - the cell membrane. Therefore they say that the membrane has three-layer structure : proteins-fat-proteins. Inside the cell there are also many similar fatty membranes that divide its internal space into compartments. The same membranes surround cellular organelles: nucleus, mitochondria, chloroplasts. So the membrane is a universal molecular structure common to all cells and all living organisms.

On the left is no longer a real, but an artificial model of a piece of a biological membrane: this is an instantaneous snapshot of a fatty phospholipid bilayer (i.e., a double layer) in the process of its molecular dynamics simulation. The calculation cell of the model is shown - 96 PC molecules ( f osphatidyl X olina) and 2304 water molecules, for a total of 20544 atoms.

On the right is a visual model of a single molecule of the same lipid from which the membrane lipid bilayer is assembled. At the top it has a hydrophilic (water-loving) head, and at the bottom there are two hydrophobic (water-afraid) tails. This lipid has a simple name: 1-steroyl-2-docosahexaenoyl-Sn-glycero-3-phosphatidylcholine (18:0/22:6(n-3)cis PC), but you don't need to remember it unless you you plan to make your teacher faint with the depth of your knowledge.

A more precise scientific definition of a cell can be given:

is an ordered, structured, heterogeneous system of biopolymers bounded by an active membrane, participating in a single set of metabolic, energy and information processes, and also maintaining and reproducing the entire system as a whole.

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

The cell membrane (plasmalemma, plasmolemma) is an active membrane that separates the cell from the environment and connects it with the environment. © Sazonov V.F., 2016.

From this definition of a membrane it follows that it not only limits the cell, but actively working, connecting it with its environment.

The fat that makes up the membranes is special, so its molecules are usually called not just fat, but "lipids", "phospholipids", "sphingolipids". The membrane film is double, that is, it consists of two films stuck together. Therefore, in textbooks they write that the basis of the cell membrane consists of two lipid layers (or " bilayer", i.e. a double layer). For each individual lipid layer, one side can be wetted with water, but the other cannot. So, these films stick to each other precisely with their non-wettable sides.

Bacteria membrane

The prokaryotic cell wall of gram-negative bacteria consists of several layers, shown in the figure below.
Layers of the shell of gram-negative bacteria:
1. Internal three-layer cytoplasmic membrane, which is in contact with the cytoplasm.
2. Cell wall, which consists of murein.
3. The outer three-layer cytoplasmic membrane, which has the same system of lipids with protein complexes as the inner membrane.
The communication of gram-negative bacterial cells with the outside world through such a complex three-stage structure does not give them an advantage in survival in harsh conditions compared to gram-positive bacteria that have a less powerful membrane. They also do not tolerate high temperatures, increased acidity and pressure changes.

Video lecture:Plasma membrane. E.V. Cheval, Ph.D.

Video lecture:Membrane as a cell boundary. A. Ilyaskin

Importance of Membrane Ion Channels

It is easy to understand that only fat-soluble substances can penetrate the cell through the membrane fat film. These are fats, alcohols, gases. For example, in red blood cells, oxygen and carbon dioxide easily pass in and out directly through the membrane. But water and water-soluble substances (for example, ions) simply cannot pass through the membrane into any cell. This means that they require special holes. But if you just make a hole in the fatty film, it will immediately close back. What to do? A solution was found in nature: it is necessary to make special protein transport structures and stretch them through the membrane. This is exactly how channels are formed for the passage of fat-insoluble substances - ion channels of the cell membrane.

So, to give its membrane additional properties of permeability to polar molecules (ions and water), the cell synthesizes special proteins in the cytoplasm, which are then integrated into the membrane. They come in two types: transport proteins (for example, transport ATPases) and channel-forming proteins (channel builders). These proteins are embedded in the fatty double layer of the membrane and form transport structures in the form of transporters or in the form of ion channels. Various water-soluble substances that cannot otherwise pass through the fatty membrane film can now pass through these transport structures.

In general, proteins embedded in the membrane are also called integral, precisely because they seem to be included in the membrane and penetrate it through. Other proteins, not integral, form islands, as it were, “floating” on the surface of the membrane: either on its outer surface or on its inner surface. After all, everyone knows that fat is a good lubricant and it’s easy to glide over it!

conclusions

1. In general, the membrane turns out to be three-layer:

1) outer layer of protein “islands”,

2) fatty two-layer “sea” (lipid bilayer), i.e. double lipid film,

3) an inner layer of protein “islands”.

But there is also a loose outer layer - the glycocalyx, which is formed by glycoproteins protruding from the membrane. They are molecular receptors to which signaling control substances bind.

2. Special protein structures are built into the membrane, ensuring its permeability to ions or other substances. We must not forget that in some places the sea of fat is permeated through and through with integral proteins. And it is the integral proteins that form special transport structures cell membrane (see section 1_2 Membrane transport mechanisms). Through them, substances enter the cell and are also removed from the cell to the outside.

3. On any side of the membrane (outer and inner), as well as inside the membrane, enzyme proteins can be located, which affect both the state of the membrane itself and the life of the entire cell.

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

In medicine, membrane proteins are often used as “targets” for drugs. Such targets include receptors, ion channels, enzymes, and transport systems. Recently, in addition to the membrane, genes hidden in the cell nucleus have also become targets for drugs.

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.)

Cell membrane - molecular structure that consists of lipids and proteins. Its main properties and functions:

separation of the contents of any cell from the external environment, ensuring its integrity;
control and establishment of exchange between the environment and the cell;
intracellular membranes divide the cell into special compartments: organelles or compartments.

The word "membrane" in Latin means "film". If we talk about the cell membrane, then it is a combination of two films that have different properties.

The biological membrane includes three types of proteins:

Peripheral – located on the surface of the film;
Integral – completely penetrate the membrane;
Semi-integral - one end penetrates into the bilipid layer.

What functions does the cell membrane perform?

1. The cell wall is a durable cell membrane that is located outside the cytoplasmic membrane. It performs protective, transport and structural functions. Present in many plants, bacteria, fungi and archaea.

2. Provides a barrier function, that is, selective, regulated, active and passive metabolism with the external environment.

3. Capable of transmitting and storing information, and also takes part in the reproduction process.

4. Performs a transport function that can transport substances into and out of the cell through the membrane.

5. The cell membrane has one-way conductivity. Thanks to this, water molecules can pass through the cell membrane without delay, and molecules of other substances penetrate selectively.

6. With the help of the cell membrane, water, oxygen and nutrients are obtained, and through it the products of cellular metabolism are removed.

7. Performs cellular metabolism through membranes, and can perform them using 3 main types of reactions: pinocytosis, phagocytosis, exocytosis.

8. The membrane ensures the specificity of intercellular contacts.

9. The membrane contains numerous receptors that are capable of perceiving chemical signals - mediators, hormones and many other biological active substances. So it has the power to change the metabolic activity of the cell.

10. Basic properties and functions of the cell membrane:

Matrix
Barrier
Transport
Energy
Mechanical
Enzymatic
Receptor
Protective
Marking
Biopotential

What function does the plasma membrane perform in a cell?

Delimits the contents of the cell;
Carries out the entry of substances into the cell;
Provides removal of a number of substances from the cell.

Cell membrane structure

Cell membranes include lipids of 3 classes:

Glycolipids;
Phospholipids;
Cholesterol.

Basically, the cell membrane consists of proteins and lipids, and has a thickness of no more than 11 nm. From 40 to 90% of all lipids are phospholipids. It is also important to note glycolipids, which are one of the main components of the membrane.

The structure of the cell membrane is three-layered. In the center there is a homogeneous liquid bilipid layer, and proteins cover it on both sides (like a mosaic), partially penetrating into the thickness. Proteins are also necessary for the membrane to allow special substances into and out of cells that cannot penetrate the fat layer. For example, sodium and potassium ions.

This is interesting -