In the table below, predict (yes or no) whether or not the E. coli lac operon will be transcriptionally active in the presence or absence of glucose or lactose as indicated and respond

Lactose Glucose Lac expression?

No Yes
Yes Yes
Yes No

to questions “a” and “b.”

a. Explain each of your answers in terms of the molecular mechanisms that are known to underlie the regulation of the lac operon.

b. Which mechanism is considered to be negative control and which is considered to be positive control? Explain.