d
(d) \(\alpha\) -helix structure is formed when the chain of \(\alpha\) -amino acid coil as a right handed screw because of the formation of hydrogen bonds between amide groups of the same peptide chain i.e., \(NH\) group in one unit is linked to carbonyl oxygen of the third unit by hydrogen bonding. This \(H-\) bonding is responsible for holding helix in a position.