Subtopic: Fundamentals of Biomolecules, enzyme kinetics
Question Statement:
Corynebacterium diphtheriae causes diphtheria in humans, only when this
bacterium is infected by
Options:
(A) phage
(B) epsilon phage
(C) T4 phage
(D) lambda phage
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Concept Analysis (GATE BT 2025 Q.12)**
**1. Governing Concept**:
- **Topic**: Biochemistry & Secondary Structure Stabilization in Proteins
- The primary stabilizing force for protein $\alpha$-helices and $\beta$-pleated sheets is **hydrogen bonding between the backbone peptide groups**:
- Specifically between the carbonyl oxygen ($C=O$) of one peptide bond and the amide hydrogen ($N-H$) of another peptide bond.
- In an $\alpha$-helix: intrachain hydrogen bonds form between residue $i$ and residue $i+4$.
- In a $\beta$-sheet: interstrand or intersegment hydrogen bonds form perpendicular to the chain direction.
**2. Option Analysis**:
- **Option (A) is INCORRECT**: Hydrophobic interactions drive tertiary folding (tertiary hydrophobic core), not primary secondary structure definitions.
- **Option (B) is INCORRECT**: Disulfide bonds stabilize tertiary/quaternary structures.
- **Option (C) is CORRECT**: Backbone amide-to-carbonyl hydrogen bonding defines secondary structure elements.
- **Option (D) is INCORRECT**: Van der Waals interactions alone do not confer secondary structural geometry.
**3. Final Answer**:
- **Correct Choice**: **C**
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