Cell Membrane

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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.

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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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