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.
Molecular
composition:
The plasma membrane is
composed of:
·
Phospholipids.
·
Cholestrol.
·
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.
Functions:
1)
Cell membrane maintains the structural
integrity of cell.
2)
It controls movements of substances in
and out of the cell (selective permeability).
3)
It regulates cell-to-cell interactions.
4)
Its function is recognition, via
receptors, antigens, foreign cells, as well as altered cells.
5)
It acts as interface between cytoplasm
& external milieu.
6)
It establishes transport system for
specific molecules.
7)
It functions in transducing
extracellular physical and or chemical signals into intracellular events.
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