Question

Which of the following would be correct? Check all that apply.
A) The repressor for the galA gene would bind to DNA in the presence of galactose.
B) The repressor for the galA gene would not bind to DNA in the presence of galactose.
C) The repressor for the galA gene would bind to DNA in the absence of galactose.

D) The repressor for the galA gene would not bind to DNA in the absence of galactose.

Answer 1

This is the first part of the question: Consider the following genes in a hypothetical bacterium:

galA – encodes an enzyme that is required for cells to digest the sugar galactose
argB – encodes an enzyme that is required for cells to produce the amino acid arginine

Answer 2

A) False. Presumably if you have all the genes you'd need to process galactose into energy you wouldn't want to repress the genes capable of doing so when galactose is around.

B) True. If galactose is around you'll want to start transcribing the genes you'll need to process it into energy.

C) True. The repressor for galA most likely has some sort of binding site for galactose and undergoes a conformational change upon binding galactose. If there's no galactose around then the galA repressor should be capable of binding the galA promotor site and thus blocking transcription.

D) False. If the repressor isn't binding to the galA promotor then there should be expression. If there's no galactose in the environment, the repressor should be preventing transcription.

Answer 3

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