Any of various tough, fibrous proteins found in bone, cartilage, skin, and other connective tissue of vertebrates. Boiling with water converts collagen to gelatin.

Collagens have great tensile strength, and provide these body structures with the bility to withstand forces that stretch them.

Collagens consist of three polypeptide chains arranged in a triple helix, and are bundled together in fibers. When boiled in water, collagen is converted into gelatin.

Collagen supplies the matrix in which the calcium salts that give the bones their hardness are deposited. Collagen is the substance of cartilage and tendon.