Once a prophage is present in a bacterial genome, viral genes are reproduced every time the bacterium multiplies. Expression of viral genes, however, is inhibited by a repressor protein. Cell stress can induce the formation of proteases that degrade the repressor. What will result?

Question

A.  The virus will enter the lysogenic cycle.
B.  The bacterium will reject the viral genes.
C.  The virus will enter the lytic cycle.
D.  The bacterial genome will be denatured.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
 
Gather Content
· What do you already know about phage induction?
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
 

Answer 1

C.  The virus will enter the lytic cycle.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses phage induction.
· What type of thinking is required?
        o This question is asking you to analyze the information given, using logic, to dissect the problem and determine the answer.
 
Gather Content
· What do you already know about phage induction?
        o In a lysogen, expression of the prophage genome is repressed by a viral regulatory protein.
        o If the cell is stressed, the prophage can be derepressed, expressing the enzymes necessary for excision of the genome, and the lytic cycle can commence.
        o The switch from a lysogenic prophage to a lytic cycle is called induction because it requires turning on the gene expression necessary for the lytic cycle.
        o It can be stimulated in the laboratory by stressors such as starvation or ultraviolet radiation.
        o The molecular basis of induction is a stress-induced protease that can destroy the repressor protein that keeps the prophage silent. The normal function of this protease is to degrade a host repressor that controls DNA repair genes.
 
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o When cell stress degrades the repressor, will the bacterial genome be denatured? No, it shouldn’t affect the bacterial genome. (If anything, the protease will induce DNA repair.)
        o When cell stress degrades the repressor, will the bacterium reject the viral genes? No, this isn’t a mechanism to do that.
        o When cell stress degrades the repressor, will the virus enter the lysogenic cycle? No, it was already in the lysogenic cycle. Instead, it will express viral genes and enter the lytic cycle
 
Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
        o Did you recognize that when the repressor is degraded, then viral genes are expressed and the prophage can excise and enter the lytic cycle?