In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the repressor binding site on the operator sequence

Key Concepts

Lac Operon

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of structural genes (lacZ, lacY, and lacA) and regulatory elements, including a promoter and an operator. The operon is typically off when lactose is absent, as the repressor protein binds to the operator, preventing transcription. When lactose is present, it binds to the repressor, allowing transcription to occur.

Repressor Protein

The repressor protein is a key regulatory element in the lac operon that binds to the operator region to inhibit transcription of the operon genes. When lactose is present, it binds to the repressor, causing a conformational change that reduces its affinity for the operator, thus allowing RNA polymerase to transcribe the operon. Mutations in the repressor binding site can disrupt this interaction, leading to altered gene expression.

Operator Sequence

The operator sequence is a specific DNA region within the lac operon where the repressor protein binds. This binding prevents RNA polymerase from transcribing the downstream genes necessary for lactose metabolism. Mutations in the operator can affect the repressor's ability to bind, which can lead to either constitutive expression of the operon (always on) or complete loss of regulation, impacting the cell's ability to respond to lactose availability.