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

Verified step by step guidance

1. Understand the lac operon system: The lac operon in E. coli is a group of genes involved in lactose metabolism. It is regulated by the interaction of the repressor protein with the operator sequence. When the repressor binds to the operator, transcription of the operon genes is blocked. Lactose (or allolactose) acts as an inducer by binding to the repressor, preventing it from binding to the operator and allowing transcription.
2. Identify the mutation described: The problem specifies a mutation in the repressor binding site on the operator sequence. This means the operator sequence is altered such that the repressor protein can no longer bind to it.
3. Predict the effect of the mutation: If the repressor cannot bind to the operator, the operon will no longer be repressed, even in the absence of lactose. This results in constitutive expression of the operon genes, meaning they will be transcribed continuously regardless of environmental conditions.
4. Relate the mutation to gene transcription: Since the repressor is unable to block RNA polymerase from binding to the promoter and initiating transcription, the operon genes (lacZ, lacY, and lacA) will be transcribed at all times.
5. Summarize the outcome: The mutation in the repressor binding site on the operator sequence leads to a loss of regulation, causing the lac operon genes to be expressed constitutively, regardless of the presence or absence of lactose.

Key Concepts

Lac Operon Structure

The lac operon is a set of genes in E. coli that are involved in the metabolism of lactose. It consists of three structural genes (lacZ, lacY, and lacA) and regulatory elements, including a promoter and an operator. The operon is controlled by a repressor protein that binds to the operator, preventing transcription when lactose is absent.

Repressor Protein Function

The repressor protein is crucial for regulating the lac operon. It binds to the operator region of the operon, blocking RNA polymerase from transcribing the downstream genes. When lactose is present, it binds to the repressor, causing a conformational change that releases the repressor from the operator, allowing transcription to occur.

Mutations and Their Effects

Mutations in the repressor binding site on the operator can significantly affect gene transcription. If the binding site is altered, the repressor may not bind effectively, leading to constitutive expression of the operon genes regardless of lactose presence. This can result in the continuous production of enzymes needed for lactose metabolism, even when lactose is not available.