Kankozha M. K.

The Kazakh National Medical University named after S. D. Asfendiyarov, Republic of Kazakhstan

Structure and function of cellular membranes within the standard and under different stress influences

(Survey)

As is known, biological membranes, thin boundary structures of molecular dimensions, located on the surface of cells and subcellular particles, and also tubules and cysts, which penetrate protoplasm.

The regulation of the transport of ions, sugar, amino acids and other products of metabolism is the most important function of biological membranes.

Biological membranes are divided into the surface (the cytolemma) and intracellular. Surface membrane or cytolemma consists of the molecules of proteins and phospholipids and it’s a most constant, basic, universal for all cells membrane. Surface membrane, is the natural boundary between the intra- and extracellular space which occurs the first target on the way of acting different agents. It provides the integrity of any cell, and also it participates in the metabolism of substances between the cell and its environment.

Intracellular membranes divide cell into the specialized closed sections in which specified conditions of intracellular medium are supported.

The membrane is the structure, which provides the realization of the most important physiological and biochemical processes.

The disturbance of the functioning of biological membranes can be the consequence of the development of pathologic processes.

All membranes have the identical plan of structure, in spite of the variety of biological functions, forms and sizes.

The membranes distinguished in protein compositions which strictly determine their functional properties. All diaphragm proteins can be divided into three groups: ferments, receptor proteins and structural proteins. In the different membranes there is a characteristic collection of ferments. For example, K-Na-dependent adenosine triphosphate which participates in the transport of ions is localized in the plasmatic membrane.

For learning the surface of adjacent cells, viruses and etc. receptor proteins specifically connected with these or other substances.

Structural proteins are connected with the diverse protein structures of cytoplasm and supply the strength of the membrane. For example, the special proteins of plasmatic membrane in the epithelial cells are connected with the elements of cytoskeleton; participate in the formation of a whole series of the intercellular connections, such as desmosomes, adhesive contacts and other.

Depending on type of membranes the weight ratio of proteins and lipids in membranes comprises 1:4 or 1:3, and it’s also established the dependence on the specific belonging of organism.

The ratio of phospholipids and proteins differs in different organs, for example, in the microsomes of a brain ratio of phospholipid/protein as much as possible and in microsomes of a liver and muscular tissue is registered the minimal ratio.

During the adaptation to the exogenous factors and pathologic disturbances the content of separate components (phospholipids) in the membrane changes, which causes expressed changes in the microviscosity of the membranes. Such reconstructions supply the structural-functional characteristics of diaphragm proteins and diverse functions of the membranes.

The activation of the lipolytic enzymes is one of the most important mechanisms of the regulation of phospholipid composition and integrity of the structure of the biological membranes, in the cells of mammals in which they are most common phospholipase.

The activity of the lipolytic enzymes and content of free fatty acids in the cell are subjected to the seasonal changes, connected with increase or decrease in ambient temperature. The increased activity of these ferments causes a change in the content of diaphragm phospholipids, an increase in the liberation of free fatty acids and the accumulation of the peroxide products of lipoperoxidation.

The most important reason in intensifying the activity of phospholipases is the process of the peroxide oxidation of lipids. This process is necessary for cells for the normal functioning and those considerably activating during the adaptation of organism to the extreme actions of environment and pathologic states.

The membranes are capable to support the constancy of organization and properties of the molecules against the dynamics of microscopic states. They also modify the states of proteins and lipids and overcome barrier. These properties designate the structural mobility of biological membranes.

Structural reconstructions of the membranes are connected with a change of permeability of ions. For example, at ischemic disease the exchange of phospholipids is disrupted, permeability of sarcolemma of cardiomyocytes to calcium ions increases, receipt of sodium inside the cells of myocardium and an exit from them of potassium ions is strengthens.

Structural diaphragm changes are the most important mechanism in the regulation of diverse processes within the standard, during the adaptation of organism to different ecological conditions, to stress and with the pathology (for example, with hypoxia).

Thus, biological membranes as the basic structural elements of cell serve as not simply physical boundaries, but are dynamic functional surfaces.

List of the literature:

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2. Dreval V.I. «Influence of calcium on the peroxide oxidation of lipids in the plasmatic membranes». The biochemical periodical of Ukraine. 1991 year. Tom 63, No.5, pages 109-112.

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