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Question #46408
The Question
In an industrial bioreactor, a recombinant strain of E. coli is cultured to produce a therapeutic human protein. The gene of interest is cloned downstream of a wild-type lac promoter on a plasmid. The culture medium is initially supplemented with both glucose and lactose. During the early exponential growth phase, the yield of the recombinant protein is found to be negligible. What is the precise molecular mechanism responsible for this transcriptional repression?
Options
- A.
Allolactose fails to bind the repressor protein due to competitive inhibition by glucose at the repressor's allosteric site.
- B.
Glucose inhibits adenylate cyclase, leading to low cAMP levels, which prevents the CAP-cAMP complex from facilitating RNA polymerase binding.
- C.
The presence of glucose induces the synthesis of a corepressor that binds to the operator, permanently silencing the heterologous gene.
- D.
Glucose metabolism rapidly depletes intracellular ATP, preventing the ATP-dependent unwinding of the lac promoter by RNA polymerase.
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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|Plasmid vs Chromosomal DNA|Ori Sequence Stringency
Why This Question Is Tricky
Common Mistakes
Conceptual Pivot: Students often oversimplify the NCERT concept to 'Lactose present = Operon ON' (removal of negative control).
The trap lies in ignoring the positive control mechanism (Catabolite Repression).
Even if lactose inactivates the repressor, the overriding presence of glucose prevents the necessary CAP-cAMP complex formation, keeping transcription effectively 'switched off'.
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 |