Question

Describe the fluid mosaic model of cell membrane. State its function.

Answer 1

Hint: The plasma membrane or the cell membrane is outermost of almost all the cells either prokaryotic or Eukaryotic. It protects the cell cytoplasm, nucleus and cell organelles from external environments.

Complete answer:
For a long time the structure of plasma membranes was unknown; it was a question of debate. To solve the question, models of plasma membranes were proposed at different time periods. Out of those membrane models, the fluid mosaic model is most accepted because it was proved by x-ray studies also.
This model was proposed by Singer and Nicolson in 1972. According to this model, the membrane is made up of lipid- bilayer and the proteins are embedded in between lipid bilayer randomly. The polar heads of phospho-lipids are located towards the outside on both sides of the membrane and the nonpolar tails are located towards the core or center of the membrane. The proteins, according to this model, are of two types - extrinsic and intrinsic proteins. The extrinsic or peripheral proteins are present on the surface of the membrane and can be removed easily while the intrinsic or integral proteins are tightly bound in lipid bilayer that cannot be removed easily. It helps in transport of lipid soluble substance and to some extent water soluble substance (semipermeable membrane).


Note:
According to this model, the proteins are freely movable in the lipid bilayer, so they are called as fluid. The overall structure of the plasma membrane looks like mosaic, a design of the floor, so it is called a fluid mosaic model.