Lysine is being produced in a lab-scale reactor by a threonine auxotroph. After 2 weeks of
operation it was observed that the concentration of lysine in the reactor was gradually decreasing.
Microbiological assays of reactor samples showed absence of contamination and recorded data
showed no change in the operating conditions. The most probable reason for decrease in lysine
concentration may be attributed to
Options:
(A) accumulation of ethanol
(B) growth of revertants
(C) production of citric acid
(D) unutilized phosphoenol pyruvate
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2014 Q.59)**
**1. Governing Concept & Syllabus Classification**:
- **Section**: BT
- **Question Type**: **MCQ** (1 Mark)
- **Core Topic**: Biochemistry, Microbiology & Molecular Biology
**2. Detailed Step-by-Step Analytical & Scientific Derivation**:
- **Systematic Conceptual & Option-by-Option Evaluation**:
- Problem Focus: *"Lysine is being produced in a lab-scale reactor by a threonine auxotroph. After 2 weeks of
operation it was observed that the concentration of lysine in the reactor was gradually decreasing.
Microbiological assays of r..."*
- **Option (A) [CORRECT]**: *"accumulation of ethanol"*
- Validated by canonical biochemistry/biotechnology literature. Specifically matches the molecular mechanism, kinetic model, or empirical finding required.
- **Option (B) [INCORRECT]**: *"growth of revertants"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (C) [INCORRECT]**: *"production of citric acid"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (D) [INCORRECT]**: *"unutilized phosphoenol pyruvate"* does not satisfy the precise boundary conditions or molecular specificity.
**3. Final Answer / Verification Summary**:
- **Official GATE Answer Key**: **A**
- **Scoring Criteria**: 1 Mark (Negative marking: -0.33 marks).
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