Under which conditions are the lac structural genes expressed most efficiently? View Available Hint (s)

No glucose, high lactose

No glucose, no lactose

High glucose, no lactose

High glucose, high lactose

No glucose, high lactose

Explanation:

The lac operon is regulated by both negative and positive control.

The negative control involves a repressor protein which, when no lactose is present, is bound to the operator sequence of the operon and blocking transcription of the structural genes.

When lactose is present, it binds the inhibitor causing its release from the operator and thus allowing the transcription of the genes.

The positive control involves regulation by glucose. Glucose is more easily metabolized than lactose, so when it's present the bacteria will preferrably use glucose as fuel instead of lactose, so the expression of the lac operon genes is low.

When glucose levels are high, cAMP levels are low. cAMP is needed to activate a protein called CAP (Catabolite Activator Protein) which binds to a regulatory sequence of the operon lac and increases its transcription.