Collagen in the Cells

The Collagen are found in tendons and other connective ligaments. Collagen have a triple helix as the major structure. Keratin structure is described more fully in the next section. The main differences in various keratins arise from their sulfur content. If there are many cysteine disulfide cross-links, then there is very little flexibility as in horns, claws, hooves, or nails. In wool, skin, and muscle proteins, there are fewer disulphide cross links which allow some stretching but returns to normal upon relaxation of tension.

Quaternary structure of collagen consists of three left handed helices twisted into a right handed coil. This structure is shown in the graphic on the left. Basic properties of collagen are rigidity and resistance to stretching. The helices are grouped in a variety of more complex fiber type structures. A rigid pattern of inter chain amide carbonyl hydrogen bonding is best accommodated by a primary amino acid sequence of,

-gly-X-pro- or -gly-X-hypro

X is any amino acid and hypro is hydroxyproline. In the graphic on the left X = arginine. Molecular model studies show that this sequence works the best for the triple helix structure. Glycine is needed because it is small and is the only amino acid which can fit in the interior of the triple helix