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GATE 2022 BT – Question 51

General Biology · Microbiology: Microbial growth and nutrition, operons (lac, trp, ara), nitrogen fixation · 2 marks · Multiple select

Which of the following statement(s) is(are) CORRECT regarding the lac operon in E. coli when grown in the presence of glucose and lactose?

  1. At low glucose level, the operon is activated
  2. At high glucose level, the operon is activated to enable the utilization of lactose
  3. The lac repressor binds to operator region inactivating the operon
  4. Binding of lactose to the lac repressor induces the operon

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Show answer and explanation

Correct answer: (A) At low glucose level, the operon is activated; (C) The lac repressor binds to operator region inactivating the operon

Explanation

The published key accepts A and C. Low glucose allows CAP–cAMP activation, and repressor binding to the operator is the mechanism of inactivation. High glucose causes catabolite repression. The physiological inducer is allolactose, rather than lactose binding directly as stated in D. C describes the repressor mechanism generally; its wording alongside the stated presence of lactose needs that distinction.

Official GATE 2022 answer key: https://gate2026.iitg.ac.in/doc/download/Answer_keys2022/bt_2022.pdf