Proteins are important molecular constituents of living cells. They can either play a mechanical role (fibrous proteins) or play a functional role (globular proteins). Proteins are important constituents of enzymes or their subunits. The protein structure can be studied at four levels. The primary structure denotes the linear sequence of amino acids in the polypeptide constituents of the proteins. The secondary structure denotes the structure of a local region of the polypeptide. The tertiary structure is the overall three dimensional conformation of the protein. The quaternary structure is the relative arrangement of polypeptides in a protein