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

Mutation of the lacI gene affecting the DNA-binding site of the protein

Verified step by step guidance

1. Understand the role of the lacI gene: The lacI gene encodes the lac repressor protein, which binds to the operator region of the lac operon to inhibit transcription in the absence of lactose.
2. Identify the mutation's impact: A mutation affecting the DNA-binding site of the lac repressor protein would likely prevent it from binding to the operator region.
3. Consider the consequences of the repressor not binding: If the repressor cannot bind to the operator, RNA polymerase can access the promoter and initiate transcription of the operon genes, even in the absence of lactose.
4. Predict the effect on gene transcription: The operon genes (lacZ, lacY, and lacA) would be transcribed constitutively, meaning they are expressed continuously regardless of lactose presence.
5. Summarize the overall impact: This mutation would lead to a loss of regulation of the lac operon, resulting in unnecessary energy expenditure by the cell due to the constant production of enzymes involved in lactose metabolism.

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 the promoter and operator. The operon is typically off when lactose is absent, but it is activated in the presence of lactose, allowing the bacteria to utilize this sugar as an energy source.

LacI Gene and Repressor Protein

The lacI gene encodes the lac repressor protein, which binds to the operator region of the lac operon to inhibit transcription when lactose is not present. Mutations in the lacI gene that affect the DNA-binding site can prevent the repressor from binding effectively, leading to constitutive expression of the operon, even in the absence of lactose.

Transcription Regulation

Transcription regulation in prokaryotes involves mechanisms that control the expression of genes based on environmental conditions. In the case of the lac operon, the presence of lactose leads to the inactivation of the repressor, allowing RNA polymerase to transcribe the operon genes. Mutations that alter the repressor's function can disrupt this regulation, impacting the cell's ability to respond to lactose availability.