Function and diversity

Collagen that present in all multicellular organisms is not only one protein but a family of structurally related proteins.  It is the main abundant protein in mammals and is present in most organs of the body where it serves to carry cells together in discrete units.  It is also the main ?brous part of bones, tendons, skin, cartilage, teeth and blood vessels. The various collagen proteins have very different functions. The extremely hard structures of teeth and bones contain collagen and a calcium phosphate polymer. In tendons collagen forms rope-such as ?bers of high tensile strength, although in the skin collagen forms loosely woven ?bers which can expand in all directions. The various kinds of collagen are characterized through several polypeptide compositions which are shown in below table. Each collagen is composed of three polypeptide chains that may be all identical as in types II and III or may be of two various chains types that are I, IV and V. A single molecule of type I collagen has a molecular mass of 285 kDa a length of 300 nm and a width 1.5 nm.