Question

Variable and constant region of light chain of immunoglobulins are

• A. Linked to Fc region of heavy chain
• B. Joined together with disulphide bonds
• C. Only involved in antigen binding site
• D. Almost equal in size

Hint:

Immunoglobulin Light Chain: $V_L$ domain ($\approx 110$ aa) $+$ $C_L$ domain ($\approx 110$ aa) $\approx 220$ amino acids (equal domain size).

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Immunoglobulin light chains ($\kappa$ or $\lambda$) are organized into two compact, independently folding globular immunoglobulin domains of approximately equal length.

Step 2: Detailed Explanation:
In an antibody light chain (total length $\approx 214 - 220\text{ amino acids}$, molecular weight $\approx 25\text{ kDa}$):
1. Variable Domain ($V_L$): The amino-terminal domain (spanning residues 1 to 108--110), containing hypervariable complementarity-determining regions (CDRs).
2. Constant Domain ($C_L$): The carboxy-terminal domain (spanning residues 111 to 214--220).
Both domains fold into characteristic $\beta$-sandwich immunoglobulin domain folds of almost equal size ($pprox 110$ amino acids each).

Step 3: Final Answer:
Therefore, the variable and constant regions of the light chain are Almost equal in size, matching option (D).