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 allosteric 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. The allosteric site of the lac repressor is where the inducer (allolactose) binds, causing a conformational change that prevents the repressor from binding to the operator.
2. Analyze the mutation: A mutation in the allosteric site of the lacI gene would likely affect the ability of the repressor protein to bind the inducer (allolactose). This could result in the repressor being unable to undergo the conformational change necessary to release from the operator.
3. Predict the effect on transcription: If the repressor cannot bind the inducer, it will remain bound to the operator, continuously blocking RNA polymerase from transcribing the operon genes. This would lead to a lack of transcription, even in the presence of lactose.
4. Consider alternative scenarios: If the mutation causes the allosteric site to mimic the induced state permanently, the repressor may never bind to the operator, leading to constitutive (continuous) transcription of the operon genes, regardless of lactose presence.
5. Summarize the outcomes: Depending on the specific nature of the mutation, the lac operon could either be permanently repressed (no transcription) or constitutively active (continuous transcription). The exact effect depends on whether the mutation prevents inducer binding or mimics the induced state.

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 that control their expression. The operon is typically off when lactose is absent and is activated in its presence, allowing the bacteria to utilize lactose 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. The repressor can undergo conformational changes when bound to allolactose, a lactose metabolite, allowing RNA polymerase to access the promoter and initiate transcription of the operon genes.

Allosteric Regulation

Allosteric regulation refers to the modulation of a protein's function through the binding of an effector molecule at a site other than the active site. In the context of the lac operon, mutations affecting the allosteric site of the lac repressor can disrupt its ability to bind allolactose, potentially leading to continuous repression of the operon, even in the presence of lactose.