Question

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?

Answer 1

The system of regulation in bacteriophage life cycle operates under negative control, as the temperate phage remains inactive until stressors induce the lytic cycle.

Step-by-step explanation:

The regulation of the lytic and lysogenic cycles in bacteriophages can be characterized as being under negative control. In a lysogenic cycle, a temperate bacteriophage's DNA integrates into the bacterial chromosome as a prophage. During this state, several operons maintain the prophage state by interacting with a repressor that prevents the initiation of the lytic cycle.

When environmental stressors such as ultraviolet light or toxic chemicals affect the bacterial cell, they lead to the breakdown of the repressor. This, in turn, causes the production of enzymes involved in the lytic cycle. Because the repressor actively inhibits the lytic cycle under normal conditions, and a stress-induced breakdown of the repressor is required to initiate the lytic cycle, this system of regulation is considered to be operating under negative control.

Answer 2

Romans and the Trojan war