Describe secondary and tertiary structures of alphakeratin a

Describe secondary and tertiary structures of alpha-keratin and collagen, and their differences

Solution

Alpha keratin
- Found in hair , wool nails, claws and outer layer of the skin
-right handed alpha helix
- arranged as a coiled coil
- it has two strands of alpha keratin oriented in parallel with their amino termini at the same end, wrapped in a super twisted coil
-5.15-5.2 A per turn . Helical path is left handed
- hydrophobic amino acid residues at the surface of two alpha helices
-Rich in residues of ala,val,leu,Met, and phe

Simple tertiary structure. Helical axis twisted in a left handed super helix.


Collagen
-found in tendons, cartilages, cornea of the eye
-left handed with 3 amino acids per turn
-coiled coil but unlike alpha keratin, distinct tertiary and quaternary structure
-35% gly, 11% ala and 21% pro and 4 hydroxyproline
-repeating tripeptide gly-X-Y where X is often Pro and Y is $Hyp
-super twisted quaternary structure
-Triple helix (supra molecular assembly)