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Question #46406
The Question
An E. coli mutant with a complete deletion of the lacI gene is cultured in a medium containing abundant quantities of both glucose and lactose. Which of the following statements correctly describes the transcriptional status of the lac operon and its physiological consequence in this mutant?
Options
- A.
The operon undergoes continuous basal transcription, overriding the glucose-preference mechanism and causing an unnecessary metabolic burden.
- B.
The operon is transcribed at its maximum rate because the presence of lactose directly activates the CAP-cAMP complex.
- C.
The operon remains completely repressed because the presence of glucose directly binds to the operator region to block RNA polymerase.
- D.
The operon is fully silenced because the inducer allolactose cannot bind to the operator region in the absence of the lacI gene product.
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
Glucose Repression|Lac Operon|RNA Polymerase
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often confuse the roles of negative regulation (repressor) and positive regulation (CAP-cAMP/Catabolite repression).
A common misconception is that high glucose completely blocks transcription by preventing RNA polymerase binding.
In reality, glucose only removes the positive amplifier (CAP).
If the negative block (repressor) is also removed via mutation, basal transcription persists, breaking the cell's energy-saving glucose-preference logic.
Quick Facts About This Question
Question Information
| Subject | Biology |
| Chapter | Molecular Basis of Inheritance - Class 12 |
| Concept | Glucose Repression |
| Difficulty | 8 |
| Cognitive Load | 5 |
| Target Solve Time | 120 sec |
| Access | Free |