Definition (Cell membrane): The tough, elastic membrane that limits the protoplasmic contents of a particular cell and separates them from other cells and the external environment, is called cell membrane or plasma membrane or plasmalemma.
The plasma membrane is composed of:
- Protein (50%)
- Chains of oligosaccharides covalently linked to phospholipid and protein molecules.
Structure: Several models for the plasma membrane structure have electron proposed, but ‘Fluid-mosaic’ model (Singer & Nicholson) is now generally accepted.
- Cell membrane maintains the structural integrity of cell.
- It controls movements of substances in and out of the cell (selective permeability).
- It regulates cell-to-cell interactions.
- Its function is recognition, via receptors, antigens, foreign cells, as well as altered cells.
- It acts as interface between cytoplasm & external milieu.
- It establishes transport system for specific molecules.
- It functions in transducing extracellular physical and or chemical signals into intracellular events.