ABSTRACT
Collagen is the name given to a family of structurally related proteins that form strong insoluble fibers. Collagens consist of several polypeptide chains, the identity and distribution of which vary between collagen types. The different types of collagen are found in different locations in the body. Like other secreted proteins, collagen polypeptides are synthesized by ribosomes on the rough endoplasmic reticulum. The primary structure of each polypeptide in collagen is characterized by a repeating tripeptide sequence of Gly–X–Y where X is often, but not exclusively, Pro and Y is often Hyp. The other post-translational modification that occurs to collagen is glycosylation. When the collagen polypeptides are synthesized they have additional amino acid residues on both their N and C termini that are absent in the mature collagen fiber. The strength and rigidity of a collagen fiber is imparted by covalent cross-links both between and within the tropocollagen molecules.
