Final answer:
The presence of lactose causes a conformational change in the lac repressor, preventing it from binding to the operator and allowing transcription of the lac operon.
Step-by-step explanation:
In the lac operon, the lac repressor protein binds to the operator region of the DNA, preventing the movement of RNA polymerase and thus inhibiting the transcription of the operon. However, when lactose is present, it is converted to allolactose, which binds to the lac repressor and causes a conformational change, preventing the repressor from binding to the operator. As a result, RNA polymerase can transcribe the genes of the lac operon, allowing for the production of proteins involved in lactose metabolism.
Allolactose binding to the lac repressor induces a conformational change that prevents the repressor from binding to the operator, enabling the transcription of the lac operon in the presence of lactose.
A conformational change that prevents the repressor from binding to the lac operator occurs when allolactose binds to the lac repressor. In the presence of lactose, some of the lactose is converted into allolactose, which then binds to the repressor protein. This binding changes the shape of the repressor so that it can no longer bind to the operator. Without the repressor bound to the operator, RNA polymerase is free to transcribe the lac operon genes, allowing for the digestion of lactose.
If there were a mutation in the repressor protein that prevented it from binding lactose, the repressor would remain on the operator, and transcription of the operon would be inhibited, regardless of the presence of lactose.