Collagen

Collagen is a family of fibrous structural proteins that form a major component of the extracellular matrix in connective tissues. It provides tensile strength in skin, bone, tendons, ligaments, cartilage, blood vessels, and the cornea. It is the most abundant protein in mammals, encoded by at least 28 genes, with types I, II, and III accounting for the majority of the body's collagen. Type I is common in skin, bone, and tendons; type II predominates in cartilage; type III is found in reticular fibers of skin and vessels; types IV and V contribute to basement membranes and hair.

Structure and biosynthesis: Collagen molecules form a triple helix of three polypeptide chains with repeating Gly-X-Y sequences. Hydroxyproline and hydroxylysine residues, added post-translationally, stabilize the helix. Procollagen is secreted by cells such as fibroblasts, chondrocytes, and osteoblasts, processed outside the cell to fibrils, and cross-linked by lysyl oxidase to increase strength.

Function and aging: Collagen networks provide tissue strength and aid wound healing. Turnover declines with age, contributing to wrinkles and joint stiffness. Vitamin C is required for hydroxylation; deficiency leads to defective collagen and scurvy.

Clinical and practical aspects: Collagen is used in wound dressings and biomaterials; collagen-derived peptides are sold as dietary supplements with mixed evidence for skin or joint benefits. Dietary collagen is typically hydrolyzed to amino acids and small peptides before absorption.

Sources: animal tissues such as bovine, porcine, marine, and poultry.