Section 3: Genetics, Cellular and Molecular Biology
DNA replication, transcription, translation
Subtopic: Fundamentals of DNA replication, transcription, translation
Question Statement:
During transcription in prokaryotic cells, the movement of RNA polymerase along the DNA double helix produces topological changes in the template:
Options:
(A) DNA Gyrase introduces negative supercoils and Topoisomerase I removes negative supercoils
(B) DNA Topoisomerase I introduces negative supercoils and DNA Gyrase removes negative supercoils
(C) both DNA Gyrase and DNA Topoisomerase I introduce negative supercoils
(D) both DNA Gyrase and DNA Topoisomerase I remove negative supercoils
Official Answer Key:
A
Step-by-Step Solution & Explanation
### **Official Solution & Step-by-Step Derivation (GATE BT 2010 Q.8)**
**1. Governing Concept & Syllabus Classification**:
- **Section**: Biotechnology
- **Question Type**: **MCQ** (1 Mark)
- **Core Topic**: Quantitative & Analytical Aptitude
**2. Detailed Step-by-Step Analytical & Scientific Derivation**:
- **Systematic Conceptual & Option-by-Option Evaluation**:
- Problem Focus: *"During transcription in prokaryotic cells, the movement of RNA polymerase along the DNA double helix produces topological changes in the template:..."*
- **Option (A) [CORRECT]**: *"DNA Gyrase introduces negative supercoils and Topoisomerase I removes negative supercoils"*
- Validated by canonical biochemistry/biotechnology literature. Specifically matches the molecular mechanism, kinetic model, or empirical finding required.
- **Option (B) [INCORRECT]**: *"DNA Topoisomerase I introduces negative supercoils and DNA Gyrase removes n"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (C) [INCORRECT]**: *"both DNA Gyrase and DNA Topoisomerase I introduce negative supercoils"* does not satisfy the precise boundary conditions or molecular specificity.
- **Option (D) [INCORRECT]**: *"both DNA Gyrase and DNA Topoisomerase I remove negative supercoils"* 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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