Question

Which of the following is a small unit of antigenicity?
A. Epitope
B. Paratope
C. Cofactor
D. Prosthetic group

Answer 1

Hint: The capacity of a chemical structure of an antigen to bind specifically with a group of certain products which have adaptive immunity is known as antigenicity. It can also be defined as the ability to be specifically recognized by the antibodies.

Complete Answer:
Antigenicity is the process by which antigens are recognized by the antibodies specifically. There are different factors that influence. It is also known as antigenic reactivity

Option A: Epitope is also known as ‘antigenic determinant. ’ Epitopes are basically the regions present on the antigens which interact with the antibodies, B cells and the T cells. Thus, epitope is the smallest unit of antigenicity.

Option B: Paratope is also known as the antigen binding site is basically the part of the antibody which is responsible for recognising and binding to an antigen. It is a part of the antibody’s FAB region and is made up of 5-10 amino acids.

Option C: Cofactor can be defined as a non-protein chemical compound or a metallic ion which is required from an enzyme's activity. They are also known as ‘helper molecules’ as they help in biochemical transformations of the enzymes. It has no relation with antigen.

Option D: Prosthetic group can be defined as a tightly bound and specific non-polypeptide unit which is required for the biological functioning of some proteins. It can either be organic like lipid, sugar or vitamin or inorganic such as a metal ion. It has no relation with antigen.

Thus, the correct option is A) Epitope.

Note: It is to be noted that immunogenicity and antigenicity are two different terms related to immunity. Immunogenicity is a term which refers to the ability of a substance to induce humoral or cellular immune response. On the other hand, antigenicity is the ability to be specifically recognised by antibodies.