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 to questions "a" and "b."
Lactose Glucose Lac expression?
No Yes
Yes Yes
Yes No
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.