The conformations which the polypeptide chains assume as a result of hydrogen bonding is called the secondary structure of proteins. The two types of secondary structures are α -helix and β -pleated sheet structure.
α -helix structure: In this structure, the -NH group of an amino acid residue forms H-bonds with the > c = o group of the adjacent turn of the right handed screw. (α - helix)
β - pleated sheet structure: This structure is called so because it looks like the pleated folds of a drapery. In this structure, all the peptide chains are stretched out to nearly the maximum extension and the then laid side by side. These peptide chains are held together by inter molecular hydrogen bonds.