Protiens are most complex nitrogenous organic compounds, forming about 12% of the cell contents and play an important role in biochemical reactions. The structure and conformation of protein is classified into following four types.
1. Primary Protein:
A primary protein contains any or all the twenty amino acid determines the bends and folds of the protein. As many proteins contain more than one polypeptide chains, these polypeptides are joined by disulphide bonds. Enzyme ribonuclease and hormone insulin are examples of primary protein.
2. Secondary protein:
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The next complex form is the secondary structure of protein in which the polypeptide chain is coiled to form a helical form. This helical structure is maintained by a number of hydrogen bond. In the secondary structure , when the chain is arranged like a helix, it is called α helix and when more than one chain are attached together by intermolecular hydrogen bond, it is called β pleated sheet.
3. Tertiary Protein:
further folding of helical structure into specific patterns by formation of hydrogen, ionic or disulphide bond leads to tertiary structure of protein molecule. The polypeptide chain is twisted and folded to produce a stable three dimensional structure, e.g. myoglobin.
4. Quaternary Protein:
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When more than one polypeptide chain associate end to end or laterally to form a single unit, it is called quaternary configuration of protein, e.g. haemoglobin.