<prompt> Which of the following amino acids in a protein commonly acts as a potential O-Glycosylation site for attachment of an oligosaccharide unit -GlutamineCysteineSerineAsparagine  <response>: O-glycosylation:- Addition of oligosaccharide to hydroxyl chain of serine or threonine.N-glycosylation:- Addition of oligosaccharide to the amide nitrogen of asparagine. 