Structure of Collagen    (continued)
	• The structural unit of collagen is a tropocollagen, a supercoil made up of  3 helices, with a  molecular mass of ~285 kdal. • Each collagen helix consists of ~ 1000 amino acid residues. The helix is left-handed. It is not an a-helix. • The helix contains 3 amino acids per turn, with a pitch of 0.94 nm.