Collagen

Collagen is a major structural component of animal tissues such as skin, bone, cartilage, tendons and basement membrane. The basic collagen molecule is known as tropocollagen and it consists of three polypeptide chains called a -chains. They are intertwined to form a triple helix. Each of the three polypeptide chains having an approximate molecular weight of 100,000 is a left-handed chain by itself. These three left-handed a - chains then assume a right-handed superhelical structure of tropocollagen having an average molecular weight of 300,000. Each tropocollagen molecule is having an average length of 300 nm and a diameter of 1.5nm. In tissues these tropocollagen molecules are orderly arranged to form collagen fibrils which are formed with a distinct periodicity. Tropocollagen molecules forming fibrils are staggered by 67nm between adjacent rows. In addition, a gap of 40 nm exists between succeeding molecules.