Question

In the absence of glucose and the presence of lactose, where is the lac repressor bound?

Answer 1

Answer:

The lac repressor is not bound to the operon.

Explanation:

The lac repressor is a protein encoded by the lac I gene. In absence of lactose, the lac repressor binds to the operator sequence of the lac operon and does not allow the RNA polymerase to express the operon. However, as lactose enters the cell from the medium, the beta-galactosidase enzyme converts it into allolactose which in turn serves as an inducer of the lac operon. Binding of allolactose to lac repressor trigger conformational changes in the protein and renders it unable to bind to the operator. The RNA polymerase is allowed to express the operon.