Cell membrane is a biological membrane that separates the cells' contents from the outside environment. Generally, the structure of the cell membrane is selectively permeable so as to allow and control certain molecules, ions or particles to move in and out of the cell.
The cell membrane is generally composed of mixture of proteins and lipids. The phospholipid is structured to be a bilayer and the proteins in embedded into it. Cholesterol is also present to stiffen the cell membranes. However, cholesterol is not present in plant cell membranes.
The primary function of the cell membrane is to protect the cytoplasm from the outside environment and maintain the cellular shape. It also manages the transport of chemicals in an out of the cell.
Membranes from different sources vary in their composition. They essentially consists of lipoproteins which are special non-bonded combinations of lipids with proteins. In general, membranes contain about 60% protein and 40% carbohydrate by dry weight. Carbohydrate usually present to the extent of 1-10% of the total dry weight in glycoproteins and glycolipids.
Functions of the cell membrane: (1) Transport: A membrane which allows the passage of a solvent but not of a solute is called a semipermeable membrane.(2) Cell recognition and adhesion (3) Antigen specificity(4) Hormone receptors (5) Secretion (6) Oxidative phosphorylation (7) Endocytosis and exocytosis