In order to survive in the presence of the antibiotic tetracycline, some bacteria synthesize a protein called tetracycline-binding protein. As the name implies, this protein binds tetracycline. It is a monomeric protein with a single ligand-binding site. You have recently isolated a new pathogenic bacterium that is resistant to tetracycline, and purified the tetracycline-binding protein from this organism. You found that the Kd of the protein for tetracycline is 15 nM. At what concentration of tetracycline would the ratio of bound protein to free protein (i. e. [PL]/[P]) be 2

Keeping in mind the life cycle of bacteriophages, consider the following problem: during the reproductive cycle of a temperate bacteriophage, the viral dna inserts into the bacterial chromosome where the resultant prophage behaves much like a trojan horse. it can remain quiescent, or it can become lytic and initiate a burst of progeny viruses. several operons maintain the prophage state by interacting with a repressor that keeps the lytic cycle in check. insults (ultraviolet light, for example) to the bacterial cell lead to a partial breakdown of the repressor, which in turn causes the production of enzymes involved in the lytic cycle. as stated in this simple form, would you consider this system of regulation to be operating under positive or negative control?