Identify the statement that is NOT correct.  

The correct answer is Antigen binding site is located at C-terminal region of antibody molecules

Concept:

• Antibodies also known as immunoglobulins, antibodies are Y-shaped proteins produced by B cells and used by the immune system to identify and neutralize pathogens like bacteria and viruses.
• Each antibody molecule consists of two identical heavy chains and two identical light chains, forming a symmetrical structure.
• Heavy and light chains are connected by disulfide bonds, which provide stability to the antibody structure.
• The antigen binding site is not located at the C-terminal region; it is located at the N-terminal region of the antibody molecule, where the variable regions of the heavy and light chains come together to form the antigen-binding site.
• The constant regions of the heavy and light chains are found at the C-terminal ends of the antibody molecule and determine the class or isotype of the antibody.

Fig: Structure of an antibody molecule

Explanation:

• Option 1: "Each antibody has two light and two heavy chains" is correct. Each antibody molecule comprises two identical heavy chains and two identical light chains.
• Option 2: "The heavy and light chains are held together by disulfide bonds" is correct. Disulfide bonds between the chains provide structural integrity to the antibody molecule.
• Option 3: "Antigen binding site is located at C-terminal region of antibody molecules" is incorrect. The antigen binding site is located at the N-terminal region where the variable regions are present.
• Option 4: "Constant region of heavy and light chains are located at C-terminus of antibody molecules" is correct. The constant regions are situated at the C-terminal ends and are involved in effector functions of antibodies.