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

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, which binds to the repressor protein, allowing transcription of the genes necessary for lactose utilization.

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 has an allosteric site that can bind to lactose, causing a conformational change that reduces its affinity for the operator, thus allowing transcription of the operon. Mutations in the lacI gene can affect the repressor's function and, consequently, the regulation of the operon.

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, when lactose binds to the allosteric site of the lac repressor, it alters the repressor's shape, preventing it from binding to the operator. This mechanism is crucial for the operon's ability to respond to the presence of lactose and regulate gene transcription accordingly.