Question

The specificity in an antibody molecule is provided by the:

• A. Light chain variable region
• B. Light chain constant region
• C. Heavy chain constant region
• D. Hinge region

Hint:

The variable regions of the antibody chains are responsible for antigen recognition, whereas the constant regions determine the antibody class and mediate effector functions.

Answer 1

The Correct Option is A

Step 1: Understand the structure of an antibody.
Antibodies (immunoglobulins) are Y-shaped molecules composed of two identical heavy chains and two identical light chains. Each chain has a variable region (for antigen binding) and a constant region (for effector function). The variable regions determine antigen specificity.

Step 2: Examine the regions of the antibody.

• Light chain variable region: ✅ Correct. This region binds directly to the antigen and determines the antibody's specificity.
• Light chain constant region: ❌ Plays a role in structure and isotype function, not antigen specificity.
• Heavy chain constant region: ❌ Involved in effector functions (e.g., complement activation), not in antigen recognition.
• Hinge region: ❌ Provides flexibility to the antibody but does not determine antigen specificity.

Step 3: Conclusion.
The specificity of an antibody is primarily determined by the light chain variable region, as it directly participates in recognizing and binding to specific antigens.

Correct Answer: Option (1)