Plasma membrane or plasmalemma

Cytology

Cytology is the science about a cell.

The cell

The cell is the basic structural and functional unit of all multicellular organisms, limited to an active cell membrane and consisting of cytoplasm and a nucleus. The cell is open, automatically adjusting and self reproductive system.

The cytoplasm is a complex colloidal system. The cytoplasm of a cell consists of organelles, inclusions and hyaloplasm. The structure of hyaloplasm includes water, proteins, nucleinic acids, different polysaccharides and a lot of enzymes. The colloid system of hyaloplasm can be in a liquid or gel consistence.

Plasma membrane or plasmalemma

Figure 1. Diagram of a plasma membrane

The cell membrane (or plasma membrane or plasmalemma) is an universal system

which form many structures of a cell. Each cell is bounded by a cell membrane. The structure of each membrane includes proteins, lipids and carbohydrates. Proteins make 50-60% of its weight, lipids 30-40 % and carbohydrates 5-10%. Cell membrane is about 7, 5 nm thick and appears as a trilaminar structure, of two thin, dense lines and light area in the middle. The inner and the outer dense line composed of a single layer of phospholipids, between them settle some proteins. Carbohydrates are present at the surface of the plasma membrane. This layer is referred to as the cell coat or glycocalyx.

The plasmalemma and other membranes of a cell carry out some of the important functions:

1. Barrier. The plasmalemma separates a cell from an environment and other cells; the nucleus is separated from cytoplasm, membranes organelles from hyaloplasm.

2. Receptor on a surface of plasmalemma. There are special structures-receptors due to which the cell finds out different chemical substances, physical factors, other cells, hormones and antigens.

3. Transport -through a membrane of cell freely passes water, salts and substances with low molecular weight. Such transport is called passive. The transport against a gradient of concentration is called active.

Дата добавления: 2015-07-25