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Question #47729
The Question
A researcher isolates a 4 kb plasmid from E. coli. Tube A contains the untreated plasmid, while Tube B contains the plasmid treated with a restriction endonuclease having a single recognition site. Both samples are subjected to agarose gel electrophoresis, and the desired bands are subsequently excised. Which of the following statements is correct regarding their migration pattern and processing?
Options
- A.
DNA in Tube A migrates slower than Tube B because circular DNA gets entangled in the agarose matrix, and both are eluted using ethidium bromide.
- B.
DNA in Tube A migrates faster than Tube B due to its compact supercoiled conformation reducing hydrodynamic drag, and elution involves extracting these bands from the gel piece.
- C.
Both tubes will show bands at the exact same distance because migration is solely dependent on the 4 kb molecular weight, after which elution is performed by exposing the gel to UV light.
- D.
DNA in Tube B migrates faster because linear DNA threads through the gel pores more efficiently, followed by elution using a chilled ethanol spooling technique.
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
Ori_Sequence_Stringency|Taq_Polymerase_Thermal_Stability|PCR_Primer_Design
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often memorize the NCERT line 'smaller fragments move farther' and falsely conclude that molecular weight is the sole determinant of electrophoretic mobility.
They fail to account for topological isomers where supercoiled DNA (despite having the same mass as linear DNA) has a smaller hydrodynamic radius and migrates faster.
Furthermore, the question traps students who confuse the distinct processes of staining (EtBr), visualization (UV), precipitation (spooling), and extraction (elution).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biotechnology : Principles and Processes - Class 12 |
| Concept | Ori Sequence Stringency |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |