If you were given a bacterial strain with a mutation in the promoter region of the trp operon the most likely effect would be

Question

A.  interference with RNA polymerase binding.
B.  to block the repressor from binding.
C.  derepression of the trp operon.
D.  enabling the trp operon to be expressed in the absence of tryptophan.
E.  lack of expression of just the first gene in the operon.

Clarify Question
· What is the key concept addressed by the question?
· What type of thinking is required?
· What key words does the question contain and what do they mean?

Gather Content
· What do you already know about promoters?

Consider Possibilities
· Consider the different answer options. Which can you rule out?

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

A.  interference with RNA polymerase binding.

Clarify Question
· What is the key concept addressed by the question?
        o This question addresses the promoter.
· 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.
· What key words does the question contain and what do they mean?
        o The promoter region is the region of a gene where the RNA polymerase binds and initiates transcription.
        o The trp operon is a set of genes in bacteria that are transcribed together to produce enzymes for the biosynthesis of tryptophan.

Gather Content
· What do you already know about promoters?
        o A promoter is a region at the beginning of a gene, in the -35 and -10 region, that attracts the binding of RNA polymerase to initiate transcription.

Consider Possibilities
· Consider the different answer options. Which can you rule out?
        o If the promoter was mutated, would this prevent the repressor from binding? No, because the repressor binds the operator, which is downstream of the promoter.
        o If the promoter was mutated, would this cause derepression of the trp operon? In other words, prevent repression to allow expression? No, because repression depends on the repressor binding the operator, not the promoter.
        o If the promoter was mutated, would this enable the trp operon to be expressed in the absence of tryptophan? No, because that would require preventing the function of the repressor, which binds the operator.
        o If the promoter was mutated, would this cause lack of expression of just the first gene in the operon? No, because the promoter is necessary for expression of all the genes in the operon.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o What is the role of the promoter region? To allow RNA polymerase to bind and initiate transcription.
        o What binds to the promoter region? RNA polymerase.
        o So if the promoter was mutated, RNA polymerase would likely fail to bind and fail to initiate transcription.

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 This question asked what would result from a mutation in the promoter of the trp operon.
        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 the promoter is necessary for the binding of RNA polymerase?
        o Did you remember that the repressor acts on the operator region, not the promoter?