Question

A culture of lac Escherichia coli is grown in a medium lacking lactose or any other \(\beta\)-galactoside. The response of the lac operon upon induction by lactose can be monitored by measuring the levels of lac mRNA, \(\beta\)-galactosidase enzyme and permease enzyme. Which one of the following profiles correctly captures the on-off response to lactose?}

• A. P
• B. Q
• C. R
• D. S

Hint:

The lac operon is tightly regulated by the presence and absence of lactose. In the presence of lactose, lac mRNA, PE, and BG are induced. When lactose is removed, their levels decrease as the operon is turned off.

Answer 1

The Correct Option is A

The lac operon in Escherichia coli responds to lactose availability. When lactose is added, it induces the transcription of the {lac} operon, leading to the production of lac mRNA, permease enzyme (PE), and \(\beta\)-galactosidase enzyme (BG). When lactose is removed, the production of these components stops, and their levels decrease.
- Option P: This profile correctly captures the on-off response to lactose. Upon lactose addition, lac mRNA, PE, and BG all show a rapid increase, and when lactose is removed, these components decrease in a manner consistent with the regulation of the lac operon. Hence, Option P is correct.
- Option Q: This profile shows a response inconsistent with the lac operon regulation, as it suggests an unusual delay or altered pattern of induction, which does not reflect the typical response observed in {lac} operon induction. Therefore, Option Q is incorrect.
- Option R: This profile shows a response where the levels of PE, BG, and lac mRNA do not decrease properly after lactose is removed, which is inconsistent with the normal response of the lac operon. Hence, Option R is incorrect.
- Option S: This profile shows the wrong pattern of induction for PE, BG, and lac mRNA, making it an inaccurate representation of the lac operon response. Therefore, Option S is incorrect.
Thus, the correct answer is (A) P, which accurately captures the typical on-off response of the lac operon to lactose.