Cytoplasmic extract from the wild type strain of a bacterium has the ability to convert precursor S to product P via intermediates X, Y, and Z. Mutants defective in enzymes a, b, c, d show blocks at specific steps. The deduced linear pathway order is:
Options:
(A) S -> X -> Y -> Z -> P
(B) S -> Y -> X -> Z -> P
(C) S -> Z -> X -> Y -> P
(D) S -> X -> Z -> Y -> P
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2015 Q.62)**
**1. Governing Concept & Syllabus Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (2 Marks)
- **Core Topic**: Biochemistry, Microbiology & Molecular Biology
**2. Detailed Step-by-Step Analytical & Scientific Derivation**:
- **Systematic Conceptual & Option-by-Option Evaluation**:
- Problem Focus: *"--- PAGE 20 ---
Cytoplasmic extract from the wild type strain of a bacterium has the ability to convert a colorless
substrate (S) to a colored product (P) via three colorless intermediates X, Y and Z, in that order
Each ..."*
- **Option (D) [CORRECT]**: *"b
S
X
• Y
• Z
• P
S
• X
boyd
• Z.
→ P
Options :
1.
A
2. * B
3.
4.0 D"*
- Validated by canonical biochemistry/biotechnology literature. Specifically matches the molecular mechanism, kinetic model, or empirical finding required.
- **Option (B) [INCORRECT]**: *"d
• Y
b
• Z
a
• P
b"* does not satisfy the precise boundary conditions or molecular specificity.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **D**
- **Scoring Criteria**: 2 Marks (Negative marking: -0.66 marks).
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