Which of the Following BEST Describes Transcriptional Regulation of the Lac

Question

Which of the following BEST describes transcriptional regulation of the lac operon in E. coli?
A) On in the presence of lactose
B) On in the presence of lactose and presence of glucose
C) Off in the presence of glucose
D) On in the absence of lactose and presence of glucose
E) On in the presence of lactose and absence of glucose

Accepted Answer

Transcriptional regulation of the lac operon in E. coli involves the lac repressor protein binding to the operator region of the DNA in the absence of lactose, preventing RNA polymerase from initiating transcription. In the presence of lactose, allolactose (an inducer) is produced and binds to the repressor, causing it to undergo a conformational change and release from the operator. This allows RNA polymerase to bind and initiate transcription. Glucose levels do not directly affect the lac operon; however, the presence of glucose can indirectly inhibit transcription by repressing the expression of the lac operon through catabolite repression. Therefore, the lac operon is on in the presence of lactose and absence of glucose.