<prompt> In vitamin C deficiency, post translational modification of which amino acid is defective:LysineAlanineGlycineArginine.  <response>: Ans. is a i.e. Lysine : Collagen molecule is a triple helical structure consisting of three polypeptide chains wrapped around each other.Each polypeptide chain is made up ofGlycine most abundant amino acid in collagenProlineHydroxyproline HydroxylysineHydroxyproline and hydroxylysine residues occur in collagen because of post - translational modification of newly synthesised collagen molecule.The proline and lysine residues are hydroxylated to hydroxyproline and hydroxylysineThe Hydroxylation process requires:-Molecular oxygen A reducing agent such as vit. CIn case of vit. C deficiency Scurvy , collagen fibres cannot be cross-linked because hydroxyproline is required for cross- linking greatly decreasing the tensile strength of the assembled fibres.Also knowTypes of CollagenThere are four major types of collagen found in various tissues:Types - representative tissuesI - Skin, bones, tendon, blood vessels, cornea.II - Cartilage, intervertebral discs, vitreous bodyIII - fetal skin, Blood vesselsIV - Basement membrane 