Glycoproteins: Glycoproteins consists of oligosaccharide chains which are covalently attached to the polypeptide side chains. The saccharide chains, referred to as glycans, can be linked to the polypeptide in two major ways. The first class of glycoproteins is the O-linked glycans. These usually contain an N-acetylgalactosamine which is attached through a glycosidic bond to the O-terminus of either threonine or serine. The other classes of glycoproteins are the N-linked glycans. These involve a glycosidic bond between N-acetylglucosamine and the N-terminus of an asparagine residue