In antibody–antigen interactions, what is the role of the epitope and paratope?

• A. An epitope is the part of the antibody that binds antigen; paratope is the corresponding site on the antibody.
• B. Paratope is the region of antigen bound by the antibody; epitope is the corresponding site on the antibody.
• C. Antibodies bind specific epitopes on antigens via their paratopes.
• D. Antibodies bind non-specifically to most proteins.

Answer: (D)

Recognition hinges on the epitope–paratope interaction. An epitope is the specific region of an antigen that is recognized by an antibody. The paratope is the antibody’s binding site, formed mainly by the variable regions of the heavy and light chains, that fits and contacts that epitope. This interaction is highly specific—the paratope is shaped and charged to match its particular epitope, like a key fitting a lock. Epitopes can be linear or conformational, but in either case, binding occurs through the paratope, enabling the antibody to recognize and bind its target precisely. Because of this specificity, antibodies do not bind non-specifically to most proteins; binding is driven by the precise fit between paratope and epitope.