Question

In the function of the lac operon in E. coli, the lac genes are transcribed in the presence of lactose because 1. RNA polymerase binds to the operator. 2. the repressor protein binds to the operator. 3. allolactose binds to the repressor. 4. CAP does not bind to the operator. 5. of the absence of cAMP.

Answer 1

Answer: 1,3&4

Step-by-step explanation:

The lac operon is induced by lactose in the absence of glucose, this is because when lactose is present in the medium, lactose binds to the repressor protein, one molecule on each subunit, causing a conformational change in the repressor.

The Repressor-lactose complex is in active, so the repressor does not bind to the operator site.

RNAP binds to the operator, identifies the promoter sequence and transcribe the structural genes.

RNAP can attach to the promoter site only when CAP doesn't bind the operator. In the absence of glucose in bacteria cAMP is available which combines with CAP, preventing CAP from binding the promoter site.