Question

Antigen binding site in an antibody is found between

• A. two light chains
• B. two heavy chains
• C. one heavy and one light chain
• D. either between two light chains or between one heavy and one light chain depending upon the nature of antigen

Answer 1

Answer: (C)

A typical antibody monomer has four protein chains, ie, two indentical light $(L)$ chains and two identical heavy $(H)$ chains. The chains are joined by disulphide links and other bonds to form a $Y$-shaped structure. Both the heavy $(H)$ and light $(L)$ chains have variable regions at the ends of $Y$ arms. The variable region from one light chain $(L)$ and one heavy chain $(H)$ form one antigen binding site. Hence, each antibody has two antigen binding sites.