Hydroxylation is a vital biochemical process in which a hydroxyl group (–OH) is added to a molecule. In collagen biosynthesis, hydroxylation modifies the amino acids proline and lysine, converting them into hydroxyproline and hydroxylysine. These new forms allow the collagen triple helix to form stable hydrogen bonds, giving collagen its remarkable tensile strength. The reaction requires vitamin C (ascorbic acid) as a cofactor for the enzyme prolyl hydroxylase, meaning vitamin C deficiency leads to defective collagen formation, the cause of scurvy.