Correct Answer - D
Secondary structure of proteins is mainly of two types
(i) `alpha-` helix : This structure is formed when the chain of `alpha-` amino acids coils as right handed screw (called `alpha-` helix) because of the formation of the hydrogen bonds between amide group of the same peptide chain.
(ii) `beta-` plates sheet : In this structure the chains are held together by a very large number of hydrogen bonds between `C=O` and `NH` of different chains.
