Flluid Mosaic Model of Plasma Membrane

It was well known that biomembranes can contract, expand,undergo fusion and can quickly repair  themselves. on the basis of these properties Singer and Nicolson (1972)proposed that

biomembranes are not solid but quassi fluid .according to this model the membranes do not have uniform arrangement of lipids and proteins but they are mosaic of two  There is a bilayer of phospholipid molecules proteins are present in between phospholipid molecules ,on the outer side of phospholipid bilayer and on the inner side of phospholipid bilayer. the proteins which are embedded in the phospholipid bilayer are called integral or intrinsic proteins. the proteins present on outer surface of phospholipid bilayer are called extrinsic proteins or peripheral proteins. The lipid bilayer is semi fluid .it allows the lateral movement of proteins .some proteins act as enzymes. some proteins help in active transport .some carbohydrate molecules may be attached to the phospholipid molecules forming glycolipids .the carbohydrates attached to proteins form glycoproteins