In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of the CAP binding site of the lac promoter

Question

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?

Mutation of the CAP binding site of the lac promoter

Accepted Answer

Welcome back, everybody. Here's our next question in the LAC operon. The mutation in which of the following sites prevents C AM PC R P binding and also prevents high levels of expression of the LAC operon. Choice. A lack I choice B black, Y choice C lack A and choice D cap binding site. Well, we can eliminate choices B and C right away because these are structural genes. So they're lack Y and lack A, they're structural genes controlled by the LA operon that are not involved in controlling the levels of expression of the LA operon. These are the genes that are being regulated. So they're not going to be our correct answer. So we're left with choice A black I and Choice D, the cap binding site. When we talk about the cat binding site, that is the site where when glucose levels are lowered, the result in the cell is that C A MP levels are raised. That C A MP molecule binds to the cap or C R P protein. And that complex C AM PC R P or C A MP cap binds to a cap binding site. The end result of that is that there is increased levels of transcription of the LA operon because that helps enhance the binding of R N A polymerase to the promoter. And that makes sense because you want the cell to be able to turn to lactose as an alternate form of energy when glucose levels are low. So low levels of glucose through this system lead to increased levels of the production of those genes that allow the cell to digest lactose. So our answer will be twis D the cat binding site, if there's a mutation that cap binding site and it's not properly structured, that C AM PC R P binding will be prevented since the site it binds to will be mutated. And if it can't bind, you won't have those high levels of expression. So that will be prevented as well. Just to be thorough, we will look at choice a lack I this is the gene with the lac repressor protein. If there's a mutation in that gene, the lac repressor won't be produced in a functional way and the lack genes will be continuously expressed. But that doesn't have anything to do with C IC AM PC R P binding. So it's not our correct answer. So again, which mutation will affect that binding and prevent high levels of expression of the LAC operon choice D, the cap binding site. See you in the next video

In the lac operon, what are the likely effects on operon gene transcription of the mutations described in a–e?
Mutation of the CAP binding site of the lac promoter

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Key Concepts

Lac Operon

CAP Binding Site

Transcription Regulation