General Index
Collagen
Collagen is the main component of the Collagen fibers, that constitute the structural scaffold of all
the organs of mesodermic origin (connective, cartilage, bone, fasciae, tendons, dermis, etc.). Collagen is the most abundant protein in animal
tissues.
Collagen fibers are bundles of Fibrils that seen at the electron microscope present a striated pattern. These fibrils are
formed from Tropocollagen or Collagen Monomer. Tropocollagen is a fibrous proteins composed of three interlaced helices, each having
a length of some 900 aminoacids. The structure of a tropocollagen fragment is:
Changing the display to color chain we see the three helices:
The aminoacid Glycine appears repeated every four positions (if n is glycine, n+4 is also glycine).
This fact is important from the structural point of view. Not having side chain (it is simply and hydrogen atom) and being directed
towards the interior of the helix, is is the only aminoacid that could occupy this position (other side chains would be too big). This can
be illustrated as follows:
Let's see the complete molecule with ith three helices: