(i) Primary Structure : The linear sequence of amino acids units in a polypeptide chain is called the primary structure of protein molecule. Ribonuclease an enzyme, is a protein with primary structure only.
(ii) Secondary Structure : The polypetides chain that forms a 3-dimensional structure, is called as secondary structure. It possess three forms :
(a) α helix: The coils of helix are held together by hydrogen bonds between amino acids.
(b) β helix : More than one chain lie side by side joined together by hydrogen bonds between the carboxyl group of amino acids.
(c) Collagen proteins: It is a right handed super helix formed by the twisting of three helices of polypeptide chains interwined with each other.
(iii) Tertiary Structure : The tertiary structure of protein brings distant amino acid side, chains nearer to form active sites of enzyme proteins. The tertiary structure is maintained by weak bonds, such as hydrogen, ionic and hydrophilic hydrophobic bonds, formed between one part of a polypeptide and another The biological activity of a protein molecule depends largely on the specific tertiary structure Tertiary structure is found in globular proteins.
