Question

RNA polymerase can bind to the promoter region of the DNA even when the lac repressor is bound to the operator site.

Answer 1

In the lac operon, RNA polymerase can bind to the promoter regardless of the lac repressor's presence at the operator site. Lactose presence causes the repressor to release, allowing transcription to proceed. Cellular glucose levels through cAMP-CAP complex also regulate RNA polymerase's promoter binding.

Step-by-step explanation:

Gene Expression Regulation in the lac Operon

Within the context of the lac operon, the ability of RNA polymerase to bind to the promoter site is an essential step for the initiation of transcription. RNA polymerase is not inhibited from binding to the promoter by the presence of a lac repressor bound to the operator. However, transcription by RNA polymerase begins only after certain conditions are met. When lactose is absent, the repressor protein is bound to the operator, blocking transcription. Conversely, when lactose is present, it binds to the repressor, leading to its dissociation from the operator and allowing RNA polymerase to transcribe the lac operon genes. This regulatory mechanism ensures the efficient use of resources by the bacteria, only producing enzymes for lactose digestion when lactose is present.

There are other levels of control involving the catabolite activator protein (CAP) and cyclic AMP (cAMP) which further regulate the binding of RNA polymerase to the promoter. CAP must bind to the promoter for RNA polymerase to effectively initiate transcription, and this binding is conditional on the presence of cAMP, which is related to the availability of glucose in the cell.

Answer 2

RNA polymerase can bind to the promoter site even when the lac repressor is bound to the operator site. Lactose can remove the lac repressor from the operator, allowing RNA polymerase to transcribe the genes needed to digest lactose.

Step-by-step explanation:

The RNA polymerase can bind to the promoter site of the DNA even when the lac repressor is bound to the operator site. When lactose is absent, the lac repressor protein binds to the operator and prevents the RNA polymerase from transcribing the lac operon genes. However, when lactose is present, it binds to the repressor and removes it from the operator, allowing RNA polymerase to transcribe the genes needed to digest lactose.