Question

Match the number of amino acids with the respective polypeptide chains of antibodies.
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• A. A-II, B-I, C-III
• B. A-III, B-II, C-I
• C. A-II, B-III, C-I
• D. A-III, B-I, C-II

Hint:

Remember: IgM ($\mu$) and IgE ($\epsilon$) are larger than other heavy chains because they contain an extra constant domain ($C_{H}4$) instead of a hinge region.

Answer 1

The Correct Option is C

Step 1: Understanding the Concept:
Antibody molecules (immunoglobulins) are glycoproteins made of light (L) and heavy (H) polypeptide chains.
The molecular weight and length of these chains vary depending on the number of structural Ig domains they contain.

Step 2: Detailed Explanation:
Let us analyze the size of the different polypeptide chains:
Light Chains: Light chains ($\kappa$ or $\lambda$) contain two domains (one variable $V_{L}$ and one constant $C_{L}$).
They are the shortest chains, containing approximately 211 to 220 amino acids. Thus, C matches with I.
Heavy Chains: Heavy chains contain a variable domain ($V_{H}$) and several constant domains ($C_{H}$).
- The alpha ($\alpha$) chain of IgA contains four domains ($V_{H} + C_{H}1 + C_{H}2 + C_{H}3$). It has an intermediate length of approximately 450 amino acids. Thus, A matches with II.
- The mu ($\mu$) chain of IgM contains five domains ($V_{H} + C_{H}1 + C_{H}2 + C_{H}3 + C_{H}4$) and lacks a hinge region. This makes it the longest chain, containing approximately 550 amino acids. Thus, B matches with III.
Matching these pairs results in: A-II, B-III, C-I.

Step 3: Final Answer:
The correct matches are A-II, B-III, and C-I, corresponding to Option (C).