Question

When E. coli are grown on glucose,

Select one:
a. the lac genes are transcribed.
b. the laclac repressor binds to the operator of the operon.
c. lactose molecules bind to the lac repressor.
d. RNA polymerase binds to the promoter of the lac operon.

Answer 1

When E. coli are grown on glucose, the lac genes are transcribed. The lac repressor binds to the operator of the operon when glucose is present.

Step-by-step explanation:

When E. coli are grown on glucose, the lac genes are transcribed because glucose is the preferred energy and carbon source for the cells. In the presence of glucose, a repressor protein binds to the operator of the lac operon, blocking the transcription. Lactose molecules do not bind to the lac repressor. On the other hand, when glucose levels drop, RNA polymerase binds to the promoter of the lac operon and the lac genes are transcribed to allow the utilization of lactose as an alternative energy source.