Answer:
The three dimensional structure of a protein has the following levels: primary, secondary, tertiary and Quaternary.
1. Primary structure of protein is the unique order or sequence of amino acids in a polypeptide chain. The amino acids are linked together by peptide bonds.
2. Secondary structure of protein is the folding or coiling of the polypeptide chain to form a three dimensional structure. It is of two types: α-helix and β-sheets. This structure is stabilized by hydrogen bonding.
3. Tertiary structure of a protein refers to the compact globular structure stabilized by non-specific hydrophobic interactions, hydrogen bonding, salt bridges and disulfide bonds.
4. Quaternary structure of a protein is formed by the aggregation of multiple polypeptide chains. It is stabilized by non-covalent interactions and disulfide bonds.
