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Question #45871
The Question
In a hypothetical modification of the Meselson-Stahl experiment, the native DNA Polymerase of E. coli is entirely replaced by Taq polymerase. The bacteria are grown in a ^15NH_4Cl medium and then transferred to a ^14NH_4Cl medium for exactly one generation. Assuming replication successfully completes at 37°C, what anomaly would most likely be observed in the CsCl density gradient profile compared to the classic experiment?
Options
- A.
The hybrid DNA band will resolve into two distinct heavy and light bands due to the thermal properties of the polymerase.
- B.
A broad, smeared intermediate band will form because the absence of 3' to 5' exonuclease activity generates DNA with highly variable buoyant densities.
- C.
Only a single heavy ^15N-^15N band will be observed because Taq polymerase is completely inactive at mesophilic temperatures.
- D.
A perfectly sharp hybrid band will form, but it will be positioned closer to the ^14N mark due to the high processivity of the enzyme.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Comparative_Analysis
Sharpen your ability to evaluate multiple scenarios and distinguish between competing potential answers.
Concepts Behind This Question
Meselson-Stahl Density Gradient|Taq Polymerase Thermal Stability|Gel Electrophoresis Migration
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students heavily associate Taq polymerase exclusively with thermostability (PCR) and often forget its critical functional limitation: the lack of 3' to 5' proofreading activity.
The question forces students to synthesize three distinct NCERT concepts: the mechanism of the Meselson-Stahl experiment, the proofreading function of DNA polymerases, and the specific properties of Taq polymerase, linking genetic fidelity directly to the physical property of buoyant density.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Molecular Basis of Inheritance - Class 12 |
| Concept | Meselson-Stahl Density Gradient |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |