What must happen for transcription of the lac operon genes to take place?

Answer 1

Lac operon is a set of genes that regulates the digestion of lactose. In absence of lactose in the medium, the repressor protein binds to the operator that inhibit the transcription of structural genes such as beta galactosidase, lactose permease and transacetylase. This makes sure to avoid the enzyme synthesis when there is no need!
Conversely, when the lactose present in the medium, an isomer of lactose called allolactose bind to the repressor protein, the conformational change in the repressor let it to detach from repressor hence the RNA polymerase can transcribe the structural gene. Although this may be enough for synthesis of structual gene the system is tightly regulated by a protein called CAP (catabolite activator protein) and glucose.
Glucose is a preferred source of energy for cell when this desirable source is present, lactose need not be used as a energy resource. What happens is there will be low level of cAMP when there is high amount of glucose and this keeps CAP inactive.
When there is low glucose levels, the cAMP would be higher, that binds to CAP to make it active, which in turn binds to the promoter that enhance the transcription of structural genes.
Thus, for efficient transcription lac operon structural genes, lactose must be present where glucose must be absent.

Answer 2

For transcription of the lac operon genes to occur, the lac repressor must be inactivated by the presence of lactose and the absence of glucose. This allows RNA polymerase to bind to the promoter region of the lac operon and initiate transcription of the genes involved in lactose metabolism.

Answer 3

The question is incomplete. No options are given (for which of the following) to answer the question.

Answer 4

The repressor protein falls off the DNA molecule, and RNA polymerase binds to the promoter. ?

Answer 5

There must be no glucose present and only lactose.

Answer 6

must not occupy promoter