Cell membranes

Structural and chemical characterization of cell membranes

A common feature of all cell membranes is that they are thin (6-10 nm) layers of lipoprotein nature (ie lipids in complex with proteins). The principal chemical components of cell membranes are lipid (~ 40%), proteins (~ 60%) and carbohydrates (5-10%).

Refers to lipids large group of organic compounds having low water solubility (hydrophobicity), and solubility in organic solvents and fats (lipophilicity). Lipid composition is very diverse. Characteristic representatives of lipids occurring in cell membranes are phospholipids (glycerophosphatides), sphingomyelins, and steroids of lipids - cholesterol. Cholesterol depends on the stability and fluidity of the membrane.

Among the cell membrane protein is isolated so-called integral proteins, penetrating through it, and the near-membrane, or surface, not embedded in bilipidny layer. According to the biological role of membrane proteins can be divided into proteins, enzymes, carrier proteins, receptor proteins and structural.

Carbohydrates are associated with membrane lipid molecules or proteins. Such substances are called the glycolipids and glycoproteins. Their number is usually small membranes.

No matter how great the difference between the membranes in the number and composition of lipids, proteins and carbohydrates, membranes possess a number of common properties defined by their primary structure. All membranes barrier structures are drastically limiting the free diffusion of substances between the cytoplasm and the environment on the one hand, and between the membrane and the contents Hyaloplasm organelle - the other. The peculiarity of the specific functional load of each membrane is determined by the properties and characteristics of the protein components, most of which are enzymes or enzyme systems. A major role in the functioning of membrane glycoproteins and glycolipids play.

Plasmolemma. Barrier-receptor and transport system cells

Plasmolemma (plasmalemma), or outside the cell membrane, among the various cell membranes has a special place. This peripheral surface structure, not only restricts the cell from the outside, but it provides a direct connection to the extracellular medium, and hence all substances and stimuli acting on the cage.

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