Question

Quarternary structure of protein is

• A. Arrangement of amino acids in polypeptide chain
• B. Inter-relationship of amino acids in a polypeptide chain
• C. Inter-relation between polypeptide chains of a protein having more than two polypeptide chains
• D. All of the above

Answer 1

Answer: (C)

Inter-relation between polypeptide chains of a protein having more than two polypeptide chains

There are four levels of protein structure:

• Primary structure: It is the sequence of amino acids of a polypeptide chain.
• Secondary structure: It is the folding of the polypeptide chain due to the interaction between different atoms in the backbone. There are two types of secondary structures, alpha helix, and beta pleated sheet. Both these structures are stabilized by hydrogen bonds.
  
• Tertiary structure: It is the 3D structure of the protein and formed when secondary structures undergo further folding due to the interaction between R groups of different amino acids.
• Quaternary structure: It is formed by the interaction between different polypeptide chains of a single protein. So quaternary structure of proteins has more than two polypeptide chains.

So, the correct answer is 'Inter-relation between polypeptide chains of a protein having more than two polypeptide chains'.