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Question #46405
The Question
An E. coli strain is made competent using a specific concentration of divalent calcium ions and subsequently heat-shocked at 42°C to take up a recombinant plasmid. This plasmid contains a human gene of interest inserted directly downstream of a wild-type lac promoter. The transformed bacteria are then cultured in a bioreactor containing a nutrient medium rich in ampicillin, abundant glucose, and lactose. Which of the following best predicts the physiological outcome of these transformed cells?
Options
- A.
The human gene will be transcribed at maximum capacity because lactose acts as an inducer by binding to the repressor protein.
- B.
The human gene will not be transcribed efficiently because the presence of glucose prevents the positive regulation required by the lac operon.
- C.
The transformation process will fail because divalent calcium ions competitively inhibit the binding of RNA polymerase to the lac promoter.
- D.
The human gene will be expressed constitutively because the heat-shock treatment permanently denatures the lac repressor protein.
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
Allolactose|Calcium_Chloride|Heat_Shock
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students frequently conflate 'successful transformation' (physical DNA uptake) with 'successful expression' (transcription/translation).
Furthermore, the 'Trap' exploits a common half-truth: students memorize 'Lactose = Inducer' (Option A) but overlook the NCERT-Plus nuance that Glucose is the preferred substrate.
Its presence overrides lactose induction by preventing the positive regulation of the operon.
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 |