Question

The Arg genes that encode the enzymes for arginine biosynthesis are located at several positions around the genome of E.coli, and they are regulated coordinately by a transcription regulator encoded by the ArgR gene. The activity of the Arg R protein is modulated by arginine. Upon binding arginine, ArgR alters its conformation, dramatically changing its affinity for the DNA sequences in the promoters of the genes for the arginine biosynthesis. A. Given that ArgR is a repressor protein, would you expect that ArgR would bind more tightly or less tightly to the DNA sequences when arginine is absent?

Answer 1

The Arg genes is used to synthesize the arginine. Arginine is chemical building block. It is very important and is used by our body to make the proteins for our body. When the Arg ID is abundant, the expression for the biosynthetic genes must turned off. And if the ArgR behaves as the gene repressor, then the binding of the arginine increases the infinity for the regulatory sites, and allows it to the bind and then shut off the expression of the genes.

If the ArgR acts as the gene activator, then the binding of the arginine would be predicted to reduce the affinity for the regulatory DNA, and preventing the binding and the shutting off the expression for the Arg genes.