Subtopic: Fundamentals of Cell structure and signaling
Question Statement:
2-mercaptoethanol breaks the ________ covalent bond between light and heavy
chains of an immunoglobulin molecule.
Options:
(A) C-N
(B) N-O
(C) S-C
(D) S-S
Official Answer Key:
D
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2024 Q.18)**
**1. Governing Concept**:
- **Topic**: Biochemistry & Protein Structure (Reducing Agents)
- 2-Mercaptoethanol ($\beta$-ME, $\text{HS-CH}_2\text{CH}_2\text{OH}$) is a thiol reducing agent that specifically cleaves interchain and intrachain **covalent disulfide bonds** ($\text{S}-\text{S}$) between cysteine residues, separating antibody heavy and light chains into individual polypeptides.
**2. Option Analysis**:
- **Option (A) [C-N] is INCORRECT**: Peptide bonds are covalent $\text{C}-\text{N}$ bonds, cleaved by proteases, not $\beta$-ME.
- **Option (B) [N-O] is INCORRECT**: Not a stabilizing bond type in immunoglobulins.
- **Option (C) [S-C] is INCORRECT**: Thioether bonds (as in methionine) are not reduced by $\beta$-ME.
- **Option (D) [S-S] is CORRECT**: Disulfide bonds linking immunoglobulin heavy and light chains are cleaved into free sulfhydryl ($-\text{SH}$) groups.
**3. Final Answer**:
- **Correct Choice**: **D**
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