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Question #46403
The Question
In a recombinant DNA experiment, a foreign gene is ligated into a restriction site located within the lacZ gene of a plasmid vector. The transformed E. coli cells are plated on an agar medium containing Ampicillin, IPTG (an inducer), and X-gal (a chromogenic substrate). Which of the following statements is INCORRECT regarding the molecular events occurring in a white colony observed on this plate?
Options
- A.
The inducer (IPTG) successfully binds to the repressor protein, preventing it from binding to the operator region.
- B.
RNA polymerase fails to initiate transcription of the lacZ gene due to the physical disruption of the promoter by the foreign insert.
- C.
The translation of the transcribed chimeric mRNA yields a non-functional beta-galactosidase enzyme.
- D.
The cells in this colony possess the selectable marker for Ampicillin resistance but lack the ability to cleave X-gal.
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
Repressor_Protein|Selectable_Marker|LacZ_Gene
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students frequently confuse 'gene inactivation' with 'transcriptional silencing'.
Insertional inactivation disrupts the structural coding sequence, meaning transcription still occurs, but the resulting protein is non-functional.
The trap assumes students will think a disrupted gene cannot be transcribed at all, failing to distinguish between regulatory elements (promoter) and structural elements (coding sequence).
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Molecular Basis of Inheritance - Class 12 |
| Concept | Lac Operon Inducibility |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |