For an E. coli strain with the lac operon genotype I⁺&nb...

Question

For an E. coli strain with the lac operon genotype I⁺ P⁺ O⁺ Z⁺ Y⁺, identify the level of transcription of the operon genes in each growth medium listed. Specify transcription as 'none,' 'basal,' or 'activated' for each medium, and provide an explanation to justify your answer.

Growth medium contains lactose but no glucose.

Accepted Answer

Hi, everyone. Welcome back. Let's look at our next problem. What happens to the transcription process of lac operon genes when lactose is present in the growth medium but glucose is absent. Choice. A transcription process will be stopped. B transcription process will be activated. C transcription process will be delayed or d none of the options are correct. So let's think about our lack operon in these conditions. Remembering we do have that choice. B saying that none of these describe what happens. So let's look at our first condition, lactose resin and think about what happens. We recall that when lactose is present, the isomer of lactose allo lactose binds to the lac repressor protein with the result that that lac repressor is released from its binding site on the operator, meaning that R N A polymerase can now bind to the promoter. So that means of course, that transcription is now activated, but we have two conditions. So we just want to briefly go over the second, which is that glucose is absent and when glucose is absent, then C A MP levels rise that leads the formation uh the C A MP cap complex. So C A MP binds to the cap protein that binds to the cap binding site and that aids the binding of R N A polymerase to the promoter and that increases transcription. So we've got transcription activated and turned on at a high level. So since our choices are about transcription that could be stopped, activated or delayed, our answer is definitely choice. B transcription process will be activated. So A and C are incorrect and of course D is incorrect since we do have an answer choice that describes our situation. So when lactose is present, but glucose is absent. Choice B the transcription process will be activated. See you in the next video.

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