Answer :
The lac operon is a set of genes in E. coli responsible for the metabolism of lactose. Here's how the lac operon normally functions:
1. **In the absence of lactose**: When there is no lactose present in the cell's medium, a repressor protein binds to the operator region of the lac operon. This prevents RNA polymerase from transcribing the genes involved in lactose metabolism.
2. **In the presence of lactose**: When lactose is present, it acts as an inducer. Lactose is converted into allolactose, which binds to the repressor protein. This causes a conformational change in the repressor, leading to its detachment from the operator. As a result, RNA polymerase can now transcribe the genes of the lac operon, allowing the cell to metabolize lactose.
However, in the case you mentioned, where the E. coli strain transcribes the lac genes at a high level even without lactose present, there could be mutations in either the repressor gene or the operator region. These mutations might lead to the repressor protein being unable to bind effectively to the operator, allowing for continuous transcription of the lac genes regardless of lactose presence.
In summary, the normal functioning of the lac operon involves the repression of gene transcription in the absence of lactose and its induction in the presence of lactose. Mutations can disrupt this regulation, leading to constitutive expression of the lac genes, as observed in the high-level transcription without lactose in your E. coli strain.
1. **In the absence of lactose**: When there is no lactose present in the cell's medium, a repressor protein binds to the operator region of the lac operon. This prevents RNA polymerase from transcribing the genes involved in lactose metabolism.
2. **In the presence of lactose**: When lactose is present, it acts as an inducer. Lactose is converted into allolactose, which binds to the repressor protein. This causes a conformational change in the repressor, leading to its detachment from the operator. As a result, RNA polymerase can now transcribe the genes of the lac operon, allowing the cell to metabolize lactose.
However, in the case you mentioned, where the E. coli strain transcribes the lac genes at a high level even without lactose present, there could be mutations in either the repressor gene or the operator region. These mutations might lead to the repressor protein being unable to bind effectively to the operator, allowing for continuous transcription of the lac genes regardless of lactose presence.
In summary, the normal functioning of the lac operon involves the repression of gene transcription in the absence of lactose and its induction in the presence of lactose. Mutations can disrupt this regulation, leading to constitutive expression of the lac genes, as observed in the high-level transcription without lactose in your E. coli strain.
