Plasma membrane contain various proteins such as peripheral proteins,transmembrane proteins,GPI anchored proteins.Among them some protein contain carbohydrate chain basically oligosaccharide chain which is arranged in the extracellular portion of the plasma membrane.
The principle function of these oligosaccharide sidechains is to detect various chemical and biochemical signals from outside the cell .
For example integrin is a glycoprotein that detect the signal for communicating with the adjacent cells.
