Physical properties of biological membranes.

In alive cells biological membranes stay in a liquid crystal condition. In a liquid crystal properties of a crystal (the distant order of the organization) and liquids (fluidity and formation of drops) are combined, that leads to occurrence of qualitatively new properties.

The biomolecular layer phospholipids, forming biomembranes, in physiological conditions (at a body temperature, etc.) represents a liquid crystal.

At downturn of temperature and under influence of some other factors the phospholipids skeleton gets properties of a firm crystal, keeping biomolecular structure.

In physiological conditions fluidity of biological membranes decreases at increase in them maintenances of cholesterol, ions of calcium and magnesium. Local anesthetizing substances raise a degree of fluidity of cellular membranes, influencing on their liquid crystal condition. It changes at growth and development of cells, and also at some pathological conditions (a cancer, dystrophies).

Characteristic property of liquid crystals is their ability to phase transitions, i.e. to transformation to firm crystals and to returning in a former condition under certain conditions. In biological membranes phase transitions occur in physiological conditions under action of some agents. It is important, that it can be made not in all volume of a membrane, and in its small sites (there where there are such agents).

Phase transition represents cooperative process. At smooth change of force of activators physical and chemical properties of membranes change jump.

Phase transition in a phospholipids skeleton essentially changes properties of enzymes, channels, carriers and other components of a biomembrane which are being in site where cooperative process is made. There permeability changes, biochemical reactions and other processes which change a physiological condition of an organism are broken.

The basic forms of molecular movement in a biomembrane are lateral migration (moving of molecules to planes of a membrane, i.e. within the limits of one party of a biomolecular layer) and rotation of molecules around of own axis.

Unlike rotation and lateral migrations, movements of molecules across a membrane (on the one side lipid double layer on another) are made very seldom. Such kind of molecular movement name «flip-flop» - movements.

T he biomembrane as liquid crystal structure is characterized by the certain viscosity. At change of temperature, molecular structure and other parameters of a biomembrane its viscosity owing to occurrence of phase transition varies: a liquid crystal firm crystal.

Viscosity of biomembranes changes at many diseases, and also under action of electromagnetic radiations, of some pharmacological preparations, hormones. In many cases influence on viscosity of cellular membranes depends upon change of the maintenance in them of cholesterol. At a normal body temperature increase of the maintenance of cholesterol in membranes increases their viscosity, and downturn - reduces it. In it the reason of reduction of viscosity of membranes in cells of malignant tumours. Viscosity of all cellular membranes decreases under action of narcotic substances (for example, chloroform).

Viability of an organism suffers both at downturn, and at increase membrane permeability which depends upon viscosity of biomembranes. Its optimum values are supported in the cellular membranes staying in a liquid crystal condition.