Question

Predict the effect on the inducibility of the \(\operatorname{lac}\) operon of a mutation that disrupts the function of (a) the crp gene, which encodes the CAP protein, and (b) the CAP-binding site within the promoter.

Short answer

Answer: Mutations in the crp gene and the CAP-binding site would negatively affect the inducibility of the lac operon, making it harder for the bacteria to respond efficiently to the presence of lactose. This is because functional CAP protein and CAP-binding site are required for efficient activation of the lac operon. Mutations disrupting these components would significantly reduce inducibility, requiring higher concentrations of lactose for activation.

Step-by-step solution

Understand the lac operon and its regulation

The lac operon is a set of genes in bacteria, such as E. coli, that encode proteins involved in the metabolism of lactose. These genes are regulated by a promoter, which is a DNA sequence that controls transcription of the genes. The lac operon can be induced by the presence of lactose, and its inducibility is regulated by proteins such as CAP (catabolite activator protein) and lac repressor.

Understand the role of the crp gene and CAP protein in regulating the lac operon

The crp gene encodes the CAP protein, which is an important regulator of the lac operon. In the presence of a small molecule called cAMP, the CAP protein binds to a specific site on the promoter, called the CAP-binding site. When the CAP protein is bound, it helps RNA polymerase bind more efficiently to the promoter, increasing the transcription of the lac operon genes. In this way, the CAP protein acts as a positive regulator of the lac operon.

Analyze the effect of the mutation in the crp gene

A mutation that disrupts the function of the crp gene would prevent it from producing a functional CAP protein. This means that CAP would not be able to bind to the CAP-binding site in the promoter, and there would be no positive regulation of the lac operon by CAP. As a result, the inducibility of the lac operon would be significantly reduced, as it would require higher concentrations of lactose to be activated.

Analyze the effect of the mutation in the CAP-binding site

A mutation that affects the CAP-binding site within the promoter would have a similar effect as a mutation in the crp gene. This mutation would likely interfere with the CAP protein's ability to bind to the site, preventing it from promoting increased transcription of the lac operon genes. Consequently, the inducibility of the lac operon would also be significantly reduced. In summary, both mutations would negatively affect the inducibility of the lac operon, making it harder for the bacteria to respond efficiently to the presence of lactose.