If a strain of bacteria had a mutation that blocked expression of the lac repressor, what would you expect as a result?
A. The mutant strain would outcompete wildype strains, since it could always utilize lactose.
B. The mutant strain would grow at the same rate as wildtype if lactose was not present.
C. The mutant strain would waste energy producing enzymes in the absence of lactose.
D. The mutant strain would act the same, because it would still require lac activator protein to turn on.
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 the lac operon?
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?
C. The mutant strain would waste energy producing enzymes in the absence of lactose.
Clarify Question
· What is the key concept addressed by the question?
o This question addresses regulation of the lac operon.
· 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 lac repressor is a protein that binds the operator site to regulate transcription of the lac operon.
Gather Content
· What do you already know about the lac operon?
o The lac operon encodes proteins that help the cell use lactose as an energy source.
o The operon only is transcribed when lactose is present.
o When present, lactose binds the repressor protein and keeps it from binding the operator site. That allows transcription to occur.
Consider Possibilities
· Consider the different answer options. Which can you rule out?
o Would the mutant strain outcompete wildype strains, since it could always utilize lactose? No, because lactose is not always present, and it would waste energy synthesizing useless enzymes.
o Would the mutant strain would grow at the same rate as wildtype if lactose was not present? No, because it would waste energy synthesizing useless enzymes.
o Would the mutant strain would act the same, because it would still require lac activator protein to turn on? No. In fact there is no “lac activator” protein. The lac operon is controlled by the activity of the lac repressor.
Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
o Unless lactose was always present at high levels, the mutant strain would be harmed by this mutation. It would waste energy producing useless enzymes that were not needed.
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 for a bacterium mutant for the lac repressor.
o The question required you to analyze the information given, using logic, to dissect the problem and determine the answer.
o Did you remember that the lac operon encodes proteins that help the cell to utilize lactose?
o Did you recognize that the lac operon is regulated so that the cell doesn’t waste energy unless lactose is present?
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