<prompt> True about collagen is all ExceptTriple helixBeta pleated sheetVit C is necessary for post translational modificationGlycine residue at every third position  <response>: COLLAGENS HAVE A TRIPLE HELIX STRUCTUREAll collagen types have a triple helical structure. A striking characteristic of collagen is the occurrence of glycine residues at every third position of the triple helical poion of the alpha chain. This is necessary because glycine is the only amino acid small enough to be accommodated in the limited space available in the central core of the triple helix.This repeating structure, represented as Gly-X-Yn, is an absolute requirement for the formation of the triple helix. While X and Y can be any other amino acids, about 100 of the X positions are proline and about 100 of the Y positions are hydroxyproline. Proline and hydroxyproline confer rigidity on the collagen molecule. Hydroxyproline is formed by the post-translational hydroxylation of peptide-bound proline residues catalyzed by the enzyme prolyl hydroxylase, whose cofactors are ascorbic acid vitamin C and a-ketoglutarate.Ref: Harper;s Biochemistry; 30th edition; Chapter 50 The Extracellular Matrix 