The oligosaccharide units of a glycoprotein are covalently linked to the polypeptide by specific glycosidic bond, termed as the glycopeptide bond. Core protein is found in proteoglycans, not in glycoproteins. The length of the oligosaccharide chain is relatively short (2-10 sugar residues) in glycoproteins, whereas it is longer (upto 100) in proteoglycans. Glycoproteins participate in cell surface recognition