Explain secondary structure of proteins.

Explanation

The conformation which the polypeptide chain assume as a result of H-bonding between `>C= O` and -NH- groups of the peptide bond is called the secondary structure of protein. It is of following two types.
(i) (`alpha`-Halix structure. It is one of the most common ways in which a polypeptide chain form all possible bonds. In this structure the polypeptide chain twist into a right handed screw (helix) with the -NH- group of each amino acid residue H- bonded to the `> C = O` group of an adjacent turn or the helix. This type of structure is formed when size of R-groups are quite large.
`beta`-Pleated sheet structure. In this structure, all polypeptide chains are stretched out to nearly maximum extension and then laid side by side. These chains are held together by intermolecular H-bonds. As the structure resembles the pleated folds of drapery, it is called `beta`-pleated sheet structure. This type structure is formed when of the R-groups are small.