The secondary structure of a protein refers to the shape in which a long peptide chain can exist. There are two different conformations of the peptide linkage present in protein are $\alpha$ -helix and $\beta$ -conformation. The $\alpha$ -helix always has a right handed arrangement. In $\beta$ -conformation all peptide chains are streched out to nearly maximum extension and then laid side by side held together by intermolecular hydrogen bonds. The structure resembles the pleated folds of drapery and therefore is known as $\beta$ -pleated shelt.