In vitamin C deficiency, post translational modification of which amino acid is defective:

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 collagen*)ProlineHydroxyproline &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. C*In 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 Collagen*There are four major types of collagen found in various tissues:Types - representative tissues*I - Skin*, bones*, tendon*, blood vessels*, cornea*.II - Cartilage*, intervertebral discs, vitreous bodyIII - fetal skin, Blood vessels*IV - Basement membrane*