What is a membrane? The structure and functions of the membrane

What is a membrane? This concept is used in various life spheres and sciences. And in each of them it has a different meaning. But, one way or another, the use of this term is associated with the meaning of the word itself. In translation from Latin, "membrane" is a membrane.

Different interpretations of the concept

In engineering and engineering this concept is used when one speaks of a thin film or plate fixed on the contour, as in microphones or manometers.

In biology, under the membrane is meant the elastic molecular structure that exists in each cell and performs the function of protection from 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 the reverse osmosis module, which is used to purify water. This construction is a pipe having a bottom and a cover. And inside this tube is just the membrane of reverse osmosis, the presence of which ensures the production of ultrapure water, freed from various bacteriological contaminants and biological deposits. The mechanism of liquid purification is based on minimizing dead spaces in which bacteria can accumulate.

These modules have been widely used in medicine, and to be more precise, they supply the instruments for hemodialysis with ultrapure water.

Membrane accumulators and expansion tanks. Their replacement

Accumulators and expansion tanks are devices that are used to compensate for the excessive pressure (volume) inside the heating devices.

What is the 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 can vary. It can be diaphragmatic, ball and balloon. If the tank has a large volume, a metal choke is inserted into the rear of the element, in which there is an opening for bleeding air. Depending on the scope of the device, the material for the membrane is selected. For example, in the expansion tanks of the heating system, the main criterion is the level of heat resistance and durability. In the case of cold water supply, when choosing the material, the membranes are guided by the criterion of dynamic elasticity.

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

The membrane is replaced by disconnecting the accumulator or the expansion tank from the system. First, the screws that secure the flange and body are disconnected. In some devices there is still a fastening in the nipple zone. After removing it, the membrane can be easily removed. By doing reverse actions, you need to put a new membrane.

Polymer membranes

The term "polymer membrane" is used in several cases. First, it is used, speaking of one of the most modern and advanced from the point of view of practicality of roofing materials. This type of membrane is produced by applying the extrusion method, which ensures the absence of voids in the composition of the finished material. The advantages of a polymer product include absolute water resistance, vapor permeability, light weight, strength, low level of flammability, environmental safety.

The term "polymer membrane" is often used when it comes to the above-mentioned reverse osmosis plates, as well as other types of shells made from organic polymers. These are micro- and ultrafiltration products, membranes used for nanofiltration. The advantage of polymer membranes in this context is the high processability and the great possibilities of controlling the properties and structure of the material. At the same time, small chemical and technological variations of the manufacturing process are used.

Cell membrane. Cells are the units of all living things

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

A cell membrane is the border of a cell, which is a natural barrier between its internal contents and the environment. The main characteristic of the shell is the semipermeability, which ensures the penetration into the cell of moisture and nutrients 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 set up an experiment to identify the "shadows" of red blood cells. They were the first to discover the lipid bilayer during the experiments. The continuers of their work Danielli, Dawson, Robertson, Nicholson in different years worked on creating a liquid-mosaic model of the membrane structure. Finally, Singscher managed to do this in 1972.

The main functions of the cell membrane

• Separation of the internal contents of the cell from the components of the external environment.
• Contribution to the maintenance of the constancy of the chemical composition within the cell.
• Regulation of the balance of metabolism.
• Providing interconnection between cells.
• Signal function.
• Protective function.

Plasma sheath

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

A plasma membrane is characterized by a universal structure. Its boundary position causes participation in the process of selective permeability when removing 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 structure of the cell.

The finest layer, which sometimes covers the cell membrane of living organisms, is called a glycocalysis. It consists of proteins and polysaccharides. And in plant cells, the membrane from above is protected by a special wall, which also performs a supporting function and supports the form. It basically consists of fiber - an insoluble polysaccharide.

Thus, it can be concluded that the main functions of the outer cell membrane are restoration, protection and interaction with neighboring cells.

Features of the structure

What is a membrane? It is a mobile shell, the width of which is 6-10 nanomimeters. The basis of its structure is a lipid bilayer and proteins. Carbohydrates are also present in the membrane, but they account for only 10% of the mass of the membranes. But they are necessarily contained in glycolipids or glycoproteins.

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

The variety of lipid functions

Each lipid is inherently a phospholipid, formed as a result of the interaction of glycerol and sphingosine. Around the lipid frame, the membrane proteins are densely packed, but their layer is not solid. Some of them are immersed in a layer of lipids, while others seem to permeate it. This is the reason for the presence of areas that are permeable to water.

Obvious is the fact that the composition of lipids in different membranes is not accidental, but a clear explanation for this phenomenon has not yet been found. In any particular shell, up to a hundred different types of lipid molecules can be contained. Consider factors that may affect the determination of the lipid composition of the membrane molecule.

• First, a mixture of lipids must necessarily have the ability to form a stable bilayer in which proteins can function.
• Secondly, lipids should promote the stabilization of highly deformed membranes, the establishment of contact between the membranes or the binding of certain proteins.
• Thirdly, lipids are bioregulators.
• Fourthly, some lipids are active participants in biosynthetic reactions.

Cell membrane proteins

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

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

The composition of the membrane is represented, first of all, by a bimolecular layer. Its continuity provides barrier and mechanical properties of the cell. In the process of vital activity, a disruption of the structure of the bilayer can occur, which leads to the formation of structural defects of the through hydrophilic pores. After this, all the functions of the cell membrane can be disturbed.

Shell Properties

Features of the cell membrane are due to its fluidity, due to which it does not have a rigid structure. Lipids, included in its composition, can move freely. One can observe the asymmetry of the cell membrane. This is the reason for the differences in the composition of the protein and lipid layers.

The polarity of the cell membrane is proven, that is, its outer side has a positive charge, and the inner side - a negative one. It should also be noted that the shell has selective insight. It passes inside, 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 the endoplasmic reticulum are closely connected. Often the surface of the shell is covered also with various protrusions, folds, microvilli. The plasmatic membrane of the cell of animal organisms is covered externally with a glycoprotein layer that performs receptor and signal functions. In plant cells outside this shell there is another, thick and distinctly distinguishable under a microscope. Fiber, from which it is composed, participates in the formation of support in tissues of plant origin, for example, wood.

Animal cells also have external structures located outside the membrane. They perform an exclusively protective function. As an example, chitin, which is contained in the insect cover tissue, can be cited.

In addition to the cellular, there is an intracellular, or internal membrane. She divides the cell into specialized closed compartments, called organelles. They always need to maintain a certain environment.

Proceeding from the foregoing, it can be concluded that the cell membrane, the characteristics of which prove its importance in the functioning of the whole 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 sphere of science or the field of industry in which this concept is applied. In any case, this element is a shell or partition, which has flexibility and is fixed at the edges.