Question

In the lac operon, what are the likely effects on operon gene transcription of the mutations identified below? Mutation of the repressor binding site on the operator sequence.

1) Transcription is blocked.
2) Transcription is constitutive.

Answer 1

A mutation in the lac operon operator sequence that prevents repressor binding results in constitutive gene transcription, causing continuous expression of lactose metabolism enzymes. Mutations in structural genes or in the RNA polymerase binding site would disrupt or prevent lactose metabolism.

Step-by-step explanation:

In the lac operon, if the operator sequence contains a mutation that prevents the repressor protein from binding, the likely effect on operon gene transcription would be constitutive transcription. The repressor, when unable to bind to the operator, cannot prevent RNA polymerase from transcribing the structural genes of the operon. Therefore, the genes lacZ, lacY, and lacA, which are responsible for lactose metabolism, would be continuously expressed, regardless of the presence or absence of lactose in the environment.

A mutation in one of the structural genes of the lac operon would lead to the production of a nonfunctional enzyme or no enzyme at all, disrupting the metabolism of lactose within the cell. Similarly, a mutation that inhibits RNA polymerase from binding to the lac operon would result in no transcription and thus, no lactose metabolism.