Overview Covalent alterations phosphorylation kinase additions of phosphate groups glycosylation addition of oligosaccharide signals for translocation into ER/Golgi hydroxylation allows for ↑ in hydrogen bonding needed for collagen synthesis γ-carboxylation addition of carboxyl group allows for Ca2+ binding site needed for several clotting factors prenylation addition of farnesyl or geranylgeranyl lipid groups signals for membrane insertion Proteolysis cleavage of N- or C- terminal propeptides peptides beginning in "pro-" converts zymogens to mature enzymes examples enzymes ending in "-ogen"