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Question #45214
The Question
During a cloning experiment using the pBR322 vector, a foreign gene is targeted for insertion at the Pvu I site. The researcher successfully digests both the vector and the foreign DNA, mixes them, but inadvertently omits DNA ligase before transforming competent E. coli cells. Which of the following is the most scientifically accurate outcome regarding the transformed cells?
Options
- A.
Cells will grow on tetracycline but not on ampicillin, as hydrogen bonding at the sticky ends is sufficient to maintain the recombinant phenotype.
- B.
No transformed colonies carrying the plasmid will survive on either antibiotic, because the failure to catalyze phosphate esterification leaves the plasmid linear and incapable of replication.
- C.
Cells will grow on both ampicillin and tetracycline plates because the host cell's DNA polymerase will automatically seal the nicks in the absence of ligase.
- D.
Cells will exhibit insertional inactivation of the ampR gene but will survive on ampicillin due to the compensatory expression of the tetR gene.
Check Your Answer
Correct Answer
Step-by-Step Solution
Explanation
How the Examiner Thinks
Regulatory_Failure
Understand how NOT, EXCEPT, and logical constraints are used to manipulate exam results.
Concepts Behind This Question
DNA_Ligase|Restriction_Endonuclease|Antibiotic_Resistance_Genes
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students frequently confuse the annealing of sticky ends (hydrogen bonding) with the actual sealing of the DNA backbone (ligation).
The trap assumes that if sticky ends pair up, the plasmid is 'recombinant' and will replicate.
The core NCERT-Plus concept is that without the covalent phosphodiester bond formed by DNA ligase, the plasmid remains linear, is degraded by host exonucleases, and cannot confer any antibiotic resistance.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Biomolecules - Class 11 |
| Concept | Nucleotide Phosphate Esterification |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |