Since glucose is a preferred carbon source over lactose, the lac operon is able
ID: 257892 • Letter: S
Question
Since glucose is a preferred carbon source over lactose, the lac operon is able to alter the expression of genes within the lac operon based on the presence or absence of glucose. In the cell, cyclic AMP concentrations increase when glucose is absent, and cyclic AMP binds to a catabolite activator protein (CAP) which increases the expression of genes within the lac operon. What would happen to the expression of the genes from the lac operon if lactose was absent and you added cyclic AMP? Select one a. the lac operon genes would not be expressed b. none of the other answers is correct c. more than one of the other answers is correct d. some of the lac operon genes would be expressed and some would not be expressed e. the lac operon genes would be expressed oExplanation / Answer
The answer is a. The lac operon genes would not be expresssed.
Even in the presence of high levels of cAMP, as the lactose is absent here, the repressor binds to operator, as it binds to operator the RNA polymerase cannot move over the lac genes, hence the lac operon genes would not be expressed.