Cell membrane: definition, functions of membranes, physical properties. Cell membrane Figurative representation of a membrane

The concept is used in various spheres of life and sciences. Moreover, in each of them it has a different meaning. But, one way or another, the use of this term is connected with the meaning of the word itself. Translated from Latin, “membrane” is a membrane.

Different interpretations of the concept

In technology and engineering, this concept is used when talking about a thin film or plate attached along a contour, as in microphones or pressure gauges.

In biology, a membrane refers to an elastic molecular structure found in every cell that serves as protection against environmental influences. It ensures the integrity of the cell and participates in metabolic processes with the outside world.

Reverse osmosis membrane

One of the recent inventions is a reverse osmosis module, which is used to purify water. This design is a pipe with a bottom and a cover. And inside this pipe there is a reverse osmosis membrane, the presence of which ensures the production of ultrapure water, free from various bacteriological contaminants and biological deposits. The liquid purification mechanism is based on minimizing dead spaces in which bacteria can accumulate.

These modules are widely used in medicine, and to be more precise, they supply hemodialysis devices with ultrapure water.

Membranes of hydraulic accumulators and expansion tanks. Their replacement

Hydraulic accumulators and expansion tanks are devices that are used to compensate (volume) inside heating devices.

What is a membrane in this case? This element is the main component of devices of this type. It affects the performance and reliability of the entire system. The shape of the membrane may vary. It can be diaphragm, ball and balloon. If the tank has a large volume, then a metal fitting is inserted into the back of the element, which has a hole for bleeding air. Depending on the scope of use of the device, the material for making the membrane is selected. For example, in expansion tanks of a heating system, the main criterion is the level of heat resistance and durability. In the case of cold water supply, when choosing a membrane material, they are guided by the criterion of dynamic elasticity.

Unfortunately, there is no material that can be called universal. Therefore, its correct choice is one of the most important conditions for long-term operation of the device and its efficient operation. Most often, the plates are made from natural rubber, synthetic butyl or ethylene propylene rubber.

The membrane is replaced by disconnecting the accumulator or expansion tank from the system. First, the screws that hold the flange and body together are removed. Some devices also have a fastening in the nipple area. Once removed, the membrane can be easily removed. By performing the reverse steps, you need to install a new membrane.

Polymer membranes

The term “polymer membrane” is used in several cases. Firstly, it is used when talking about one of the most modern and advanced roofing materials in terms of practicality. This type of membrane is produced by using an extrusion method, which ensures that there are no voids in the finished material. The advantages of a polymer product include absolute waterproofness, vapor permeability, light weight, strength, low level of flammability, and environmental safety.

The term “polymer membrane” is often used when it comes to the reverse osmosis plates already mentioned above, as well as other types of shells made from organic polymers. These are micro- and ultrafiltration products, membranes used in nanofiltration. The advantage of polymer membranes in this context is their high manufacturability and greater ability to control the properties and structure of the material. This involves minor chemical and technological variations in the manufacturing process.

Cell membrane. Cells are the units of all living things

It has long been a known fact that the basic structural unit of a living organism is the cell. It is a differentiated section of the cytoplasm, which is surrounded by a cell membrane. In the process of evolution, as the limits of functionality expanded, it acquired plasticity and subtlety, because the most important processes in the body occur precisely in the cells.

The cell membrane is the boundary of a cell, representing a natural barrier between its internal contents and the environment. The main characteristic feature of the shell is semi-permeability, which ensures the penetration of moisture and nutrients into the cell and the removal of decay products from it. The cell membrane is the main structural component of the cell organization.

Historical facts related to the discovery and study of the cell membrane

In 1925, Grendel and Gorder successfully conducted an experiment to identify the “shadows” of red blood cells. It was they who first discovered the lipid bilayer during experiments. The continuators of their work, Danielli, Dawson, Robertson, and Nicholson, worked over the years to create a fluid-mosaic model of the membrane structure. Singher finally succeeded in doing this in 1972.

Basic functions of the cell membrane

• Separation of the internal contents of a cell from components of the external environment.
• Helps maintain a constant chemical composition within the cell.
• Regulating metabolic balance.
• Ensuring communication between cells.
• Signal function.
• Protective function.

Plasma sheath

What is the membrane called the plasma envelope? This is the outer one, which in its structure is an ultramicroscopic film with a thickness of 5-7 nanomillimeters. It consists of protein compounds, phospholipids, and water. The film, being very elastic, absorbs moisture well, and also has the ability to quickly restore its integrity.

The plasma membrane is characterized by a universal structure. Its borderline position determines its participation in the process of selective permeability during the removal of decay products from the cell. Interacting with neighboring elements and reliably protecting the contents from damage, the outer membrane is one of the most important components of the cell structure.

The thinnest layer that sometimes covers the cell membrane of living organisms is called the glycocalyx. It consists of proteins and polysaccharides. And in plant cells, the membrane is protected from above by a special wall, which also performs a supporting function and maintains its shape. It mainly consists of fiber - an insoluble polysaccharide.

Thus, we can conclude that the main functions of the outer cell membrane are repair, protection and interaction with neighboring cells.

Structural features

What is a membrane? This is a movable shell, the width of which is 6-10 nanomillimeters. Its structure is based on a lipid bilayer and proteins. Carbohydrates are also present in the membrane, but they account for only 10% of the membrane mass. But they are necessarily contained in glycolipids or glycoproteins.

If we talk about the ratio of proteins and lipids, it can vary greatly. It all depends on the type of fabric. For example, myelin contains about 20% protein, and mitochondria - about 80%. The composition of the membrane directly affects its density. The higher the protein content, the higher the shell density.

Diversity of Lipid Functions

Each lipid is a phospholipid in nature, resulting from the interaction of glycerol and sphingosine. Membrane proteins are densely located around the lipid framework, but their layer is not continuous. Some of them are immersed in the lipid layer, while others seem to penetrate it. This is the reason for the presence of areas permeable to water.

It is obvious that the composition of lipids in various membranes is not random, but a clear explanation for this phenomenon has not yet been found. Any given shell may contain up to one hundred different types of lipid molecules. Let us consider factors that may influence the determination of the lipid composition of a membrane molecule.

• Firstly, a mixture of lipids must have the ability to form a stable bilayer in which proteins can function.
• Secondly, lipids should help stabilize highly deformed membranes, establish contact between membranes, or bind certain proteins.
• Thirdly, lipids are bioregulators.
• Fourthly, some lipids are active participants in biosynthesis reactions.

Cell membrane proteins

Proteins perform several functions. Some play the role of enzymes, while others transport various substances from the environment into the cell and back.

The structure and functions of the membrane are designed in such a way that they penetrate through it, ensuring a close connection. But peripheral proteins are not too closely associated with the membrane. Their function is to maintain the structure of the shell, receive and convert signals from the external environment, and also serve as catalysts for various reactions.

The composition of the membrane is primarily represented by a bimolecular layer. Its continuity provides the barrier and mechanical properties of the cell. During life, the structure of the bilayer can be disrupted, which leads to the formation of structural defects in through hydrophilic pores. Following this, all functions of the cell membrane may be disrupted.

Shell properties

The characteristics of the cell membrane are due to its fluidity, due to which it does not have a rigid structure. The lipids included in its composition can move freely. Asymmetry of the cell membrane can be observed. This is the reason for the difference in the compositions of the protein and lipid layers.

The polarity of the cell membrane has been proven, that is, its outer side has a positive charge, and the inner side has a negative charge. It should also be noted that the shell has selective insight. It allows in, in addition to water, only certain groups of molecules and ions of dissolved substances.

Features of the structure of the cell membrane in plant and animal organisms

The outer membrane and endoplasmic reticulum of the cell are closely connected. Often the surface of the shell is also covered with various protrusions, folds, and microvilli. The cells of animal organisms are covered on the outside with a glycoprotein layer that performs receptor and signaling functions. In plant cells, outside this shell there is another one, thick and clearly visible under a microscope. The fiber from which it is composed is involved in the formation of support at the origin, such as wood.

Animal cells also have external structures located outside the membrane. They perform a purely protective function. An example is chitin, which is found in the integumentary tissue of insects.

In addition to the cellular membrane, there is an intracellular, or internal membrane. It divides the cell into specialized enclosed compartments called organelles. They must constantly maintain a certain environment.

Based on the above, we can conclude that the cell membrane, the characteristics of which prove its importance in the functioning of the entire organism, has a complex composition and structure, depending on many internal and external factors. Damage to this film can lead to cell death.

Thus, the structure and functions of the membrane depend on the field of science or industry in which this concept is applied. In any case, this element is a shell or partition that is flexible and secured at the edges.

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).

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 slide on 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.)

© 2010-2018 Sazonov V.F., © 2010-2016 kineziolog.bodhy.

The outside of the cell is covered with a plasma membrane (or outer cell membrane) about 6-10 nm thick.

The cell membrane is a dense film of proteins and lipids (mainly phospholipids). Lipid molecules are arranged in an orderly manner - perpendicular to the surface, in two layers, so that their parts that interact intensively with water (hydrophilic) are directed outward, and their parts inert to water (hydrophobic) are directed inward.

Protein molecules are located in a non-continuous layer on the surface of the lipid framework on both sides. Some of them are immersed in the lipid layer, and some pass through it, forming areas permeable to water. These proteins perform various functions - some of them are enzymes, others are transport proteins involved in the transfer of certain substances from the environment to the cytoplasm and in the opposite direction.

Basic functions of the cell membrane

One of the main properties of biological membranes is selective permeability (semi-permeability)- some substances pass through them with difficulty, others easily and even towards higher concentrations. Thus, for most cells, the concentration of Na ions inside is significantly lower than in the environment. The opposite relationship is typical for K ions: their concentration inside the cell is higher than outside. Therefore, Na ions always tend to penetrate the cell, and K ions always tend to exit. The equalization of the concentrations of these ions is prevented by the presence in the membrane of a special system that plays the role of a pump, which pumps Na ions out of the cell and simultaneously pumps K ions inside.

The tendency of Na ions to move from outside to inside is used to transport sugars and amino acids into the cell. With the active removal of Na ions from the cell, conditions are created for the entry of glucose and amino acids into it.

In many cells, substances are also absorbed by phagocytosis and pinocytosis. At phagocytosis the flexible outer membrane forms a small depression into which the captured particle falls. This recess increases, and, surrounded by a section of the outer membrane, the particle is immersed in the cytoplasm of the cell. The phenomenon of phagocytosis is characteristic of amoebas and some other protozoa, as well as leukocytes (phagocytes). Cells absorb liquids containing substances necessary for the cell in a similar way. This phenomenon was called pinocytosis.

The outer membranes of different cells differ significantly both in the chemical composition of their proteins and lipids, and in their relative content. It is these features that determine the diversity in the physiological activity of the membranes of various cells and their role in the life of cells and tissues.

The endoplasmic reticulum of the cell is connected to the outer membrane. With the help of outer membranes, various types of intercellular contacts are carried out, i.e. communication between individual cells.

Many types of cells are characterized by the presence on their surface of a large number of protrusions, folds, and microvilli. They contribute to both a significant increase in cell surface area and improved metabolism, as well as stronger connections between individual cells and each other.

Plant cells have thick membranes on the outside of the cell membrane, clearly visible under an optical microscope, consisting of fiber (cellulose). They create a strong support for plant tissues (wood).

Some animal cells also have a number of external structures located on top of the cell membrane and have a protective nature. An example is the chitin of insect integumentary cells.

Functions of the cell membrane (briefly)

Nature has created many organisms and cells, but despite this, the structure and most of the functions of biological membranes are the same, which makes it possible to examine their structure and study their key properties without being tied to a specific type of cell.

What is a membrane?

Membranes are a protective element that is an integral part of the cell of any living organism.

The structural and functional unit of all living organisms on the planet is the cell. Its life activity is inextricably linked with the environment with which it exchanges energy, information, and matter. Thus, the nutritional energy necessary for the functioning of the cell comes from the outside and is spent on its various functions.

The structure of the simplest structural unit of a living organism: organelle membrane, various inclusions. It is surrounded by a membrane, inside which the nucleus and all organelles are located. These are mitochondria, lysosomes, ribosomes, endoplasmic reticulum. Each structural element has its own membrane.

Role in cell activity

The biological membrane plays a pivotal role in the structure and functioning of an elementary living system. Only a cell surrounded by a protective shell can rightfully be called an organism. A process such as metabolism is also carried out due to the presence of a membrane. If its structural integrity is disrupted, this leads to a change in the functional state of the body as a whole.

Cell membrane and its functions

It separates the cytoplasm of the cell from the external environment or from the membrane. The cell membrane ensures the proper performance of specific functions, the specificity of intercellular contacts and immune manifestations, and maintains the transmembrane difference in electrical potential. It contains receptors that can perceive chemical signals - hormones, mediators and other biological active components. These receptors give it another ability - to change the metabolic activity of the cell.

Membrane functions:

1. Active transfer of substances.

2. Passive transfer of substances:

2.1. Diffusion is simple.

2.2. Transfer through pores.

2.3. Transport carried out by diffusion of a carrier along with a membrane substance or by relaying a substance along the molecular chain of the carrier.

3. Transfer of non-electrolytes due to simple and facilitated diffusion.

Cell membrane structure

The components of the cell membrane are lipids and proteins.

Lipids: phospholipids, phosphatidylethanolamine, sphingomyelin, phosphatidylinositol and phosphatidylserine, glycolipids. The proportion of lipids is 40-90%.

Proteins: peripheral, integral (glycoproteins), spectrin, actin, cytoskeleton.

The main structural element is a double layer of phospholipid molecules.

Roofing membrane: definition and typology

Some statistics. In the Russian Federation, membrane has been used as a roofing material not very long ago. The share of membrane roofs out of the total number of soft roof slabs is only 1.5%. Bitumen and mastic roofs have become more widespread in Russia. But in Western Europe, the share of membrane roofs is 87%. The difference is noticeable.

As a rule, the membrane as the main material when covering the roof is ideal for flat roofs. For those with a large slope it is less suitable.

The volumes of production and sales of membrane roofing on the domestic market have a positive growth trend. Why? The reasons are more than clear:

• The service life is about 60 years. Just imagine, only the warranty period of use, which is established by the manufacturer, reaches 20 years.
• Easy to install. For comparison: installing a bitumen roof takes 1.5 times longer than installing a membrane roof.
• Ease of maintenance and repair work.

The thickness of roofing membranes can be 0.8-2 mm, and the average weight of one square meter is 1.3 kg.

Properties of roofing membranes:

• elasticity;
• strength;
• resistance to ultraviolet rays and other aggressive environments;
• frost resistance;
• fire resistance.

There are three types of roofing membrane. The main classification feature is the type of polymer material that makes up the base of the canvas. So, roofing membranes are:

• belonging to the EPDM group, are made on the basis of polymerized ethylene-propylene-diene monomer, or simply put, Advantages: high strength, elasticity, water resistance, environmental friendliness, low cost. Disadvantages: adhesive technology for joining sheets using a special tape, low strength of joints. Scope of application: used as a waterproofing material for tunnel floors, water sources, waste storage facilities, artificial and natural reservoirs, etc.
• PVC membranes. These are shells in the production of which polyvinyl chloride is used as the main material. Advantages: UV resistance, fire resistance, wide range of colors of membrane fabrics. Disadvantages: low resistance to bituminous materials, oils, solvents; releases harmful substances into the atmosphere; The color of the canvas fades over time.
• TPO. Made from thermoplastic olefins. They can be reinforced or unreinforced. The former are equipped with a polyester mesh or fiberglass fabric. Advantages: environmental friendliness, durability, high elasticity, temperature resistance (both at high and low temperatures), welded joints of fabric seams. Disadvantages: high price category, lack of manufacturers in the domestic market.

Profiled membrane: characteristics, functions and advantages

Profiled membranes are an innovation in the construction market. This membrane is used as a waterproofing material.

The substance used in production is polyethylene. The latter comes in two types: high-density polyethylene (HDPE) and low-density polyethylene (LDPE).

The profiled membrane made of high-pressure polyethylene has a special surface - hollow pimples. The height of these formations can vary from 7 to 20 mm. The inner surface of the membrane is smooth. This allows for trouble-free bending of building materials.

Changing the shape of individual sections of the membrane is excluded, since the pressure is distributed evenly over its entire area due to the presence of the same protrusions. Geomembrane can be used as ventilation insulation. In this case, free heat exchange inside the building is ensured.

Advantages of profiled membranes:

• increased strength;
• heat resistance;
• resistance to chemical and biological influences;
• long service life (more than 50 years);
• ease of installation and maintenance;
• affordable price.

Profiled membranes come in three types:

• with single-layer fabric;
• with two-layer fabric = geotextile + drainage membrane;
• with three-layer fabric = slippery surface + geotextile + drainage membrane.

A single-layer profiled membrane is used to protect the main waterproofing, installation and dismantling of concrete walls with high humidity. A two-layer protective layer is used during installation. A three-layer protective layer is used on soil that is susceptible to frost heaving and on deep soil.

Areas of use of drainage membranes

The profiled membrane finds its application in the following areas:

1. Basic waterproofing of the foundation. Provides reliable protection against the destructive influence of groundwater, plant root systems, soil subsidence, and mechanical damage.
2. Foundation wall drainage. Neutralizes the effects of groundwater and atmospheric precipitation by transporting them to drainage systems.
3. Horizontal type - protection against deformation due to structural features.
4. Analogous to concrete preparation. It is used in the case of construction work on the construction of buildings in an area of ​​low groundwater, in cases where horizontal waterproofing is used to protect against capillary moisture. Also, the functions of the profiled membrane include preventing the passage of cement laitance into the soil.
5. Ventilation of wall surfaces with high humidity levels. Can be installed both on the inside and outside of the room. In the first case, air circulation is activated, and in the second, optimal humidity and temperature are ensured.
6. Inversion roofing used.

Superdiffusion membrane

The superdiffusion membrane is a new generation material, the main purpose of which is to protect roofing structure elements from wind, precipitation, and steam.

The production of protective material is based on the use of non-woven substances, dense fibers of high quality. Three-layer and four-layer membranes are popular in the domestic market. Reviews from experts and consumers confirm that the more layers a structure is based on, the stronger its protective functions, and therefore the higher the energy efficiency of the room as a whole.

Depending on the type of roof, its design features, and climatic conditions, manufacturers recommend giving preference to one or another type of diffusion membrane. So, they exist for pitched roofs of complex and simple structures, for pitched roofs with a minimum slope, for roofs with seam covering, etc.

The superdiffusion membrane is laid directly on the thermal insulation layer, the flooring made of boards. There is no need for a ventilation gap. The material is secured with special staples or steel nails. The edges of the diffusion sheets are joined and work can be carried out even under extreme conditions: in strong gusts of wind, etc.

In addition, the coating in question can be used as a temporary roof covering.

PVC membranes: essence and purpose

PFC membranes are a roofing material made from polyvinyl chloride and have elastic properties. This modern roofing material has completely replaced bitumen roll analogues, which have a significant drawback - the need for systematic maintenance and repair. Today, the characteristic features of PVC membranes make it possible to use them when carrying out repair work on old flat roofs. They are also used when installing new roofs.

A roof made of this material is easy to use, and its installation can be done on any type of surface, at any time of the year and in any weather conditions. The PVC membrane has the following properties:

• strength;
• stability when exposed to UV rays, various types of precipitation, point and surface loads.

It is thanks to their unique properties that PVC membranes will serve you faithfully for many years. The lifespan of such a roof is equal to the lifespan of the building itself, while roll roofing materials require regular repairs, and in some cases, complete dismantling and installation of a new floor.

PVC membrane sheets are connected to each other by hot welding, the temperature of which is in the range of 400-600 degrees Celsius. This connection is completely sealed.

Advantages of PVC membranes

Their advantages are obvious:

• flexibility of the roofing system, which best suits the construction project;
• durable, airtight connecting seam between membrane sheets;
• ideal tolerance to climate change, weather conditions, temperature, humidity;
• increased vapor permeability, which promotes the evaporation of moisture accumulated in the under-roof space;
• many color options;
• fire properties;
• the ability to maintain its original properties and appearance for a long period;
• PVC membrane is an absolutely environmentally friendly material, which is confirmed by relevant certificates;
• the installation process is mechanized, so it will not take much time;
• operating rules allow for the installation of various architectural additions directly on top of the PVC membrane roof itself;
• single-layer installation will save your money;
• ease of maintenance and repair.

Membrane fabric

Membrane fabric has been known to the textile industry for a long time. Shoes and clothing are made from this material: adults and children. Membrane is the basis of membrane fabric, presented in the form of a thin polymer film and having such characteristics as waterproofness and vapor permeability. To produce this material, this film is coated with outer and inner protective layers. Their structure is determined by the membrane itself. This is done in order to preserve all beneficial properties even in the event of damage. In other words, membrane clothing does not get wet when exposed to precipitation in the form of snow or rain, but at the same time, it perfectly allows steam to pass from the body into the external environment. This throughput allows the skin to breathe.

Considering all of the above, we can conclude that ideal winter clothing is made from such fabric. The membrane at the base of the fabric can be:

• with pores;
• without pores;
• combined.

The membranes, which have many micropores, contain Teflon. The dimensions of such pores do not reach the dimensions of even a drop of water, but are larger than a water molecule, which indicates water resistance and the ability to remove sweat.

Membranes that do not have pores are usually made from polyurethane. Their inner layer concentrates all the sweat and fat secretions of the human body and pushes them out.

The structure of the combined membrane implies the presence of two layers: porous and smooth. This fabric has high quality characteristics and will last for many years.

Thanks to these advantages, clothes and shoes made from membrane fabrics and intended for wear in the winter season are durable, but lightweight, and provide excellent protection from frost, moisture, and dust. They are simply irreplaceable for many active types of winter recreation and mountaineering.