A repressible operon system, like the trp operon, contai...

Question

A repressible operon system, like the trp operon, contains three genes, G, Z, and W. Operon genes are synthesized when the end product of the operon synthesis pathway is absent, but there is no synthesis when the end product is present. One of these genes is an operator, one is a regulatory protein, and the other is a structural enzyme involved in synthesis of the end product. In the table below, '+' indicates that the enzyme is synthesized by the operon and '−' means that no enzyme synthesis occurs. Use this information to determine which gene corresponds to each operon function. <>

Accepted Answer

Welcome back, everyone. Let's look at our next question. How does the end product of a repressible operon system function as a repressor choice A? It binds to the promoter region preventing R N A P memories from binding Choice B. It binds to the repressor protein activating it to bind to the operator. Choice C. It binds to the R N A polymerase preventing it from transcribing the genes or D, it binds to the operator region preventing R N A polymerase from transcribing the genes. So let's think about how a repressible operon system usually works. And it's quite frequent as this question lists that the end product itself acts as a repressor that makes it a good um negative feedback system. Because if you've built up enough or more than enough of your product, you want to be able to have that fact itself turn off further transcription. And in general, this happens when the end product binds to a repressor protein and that repo her protein generally binds to an operator and this operator will be near the promoter. And in that case, the binding of the repressor to the operator will therefore block R N a polymerase from the promoter, thereby preventing transcription. So that's sort of the usual general mechanism. So with that in mind, let's work through our answer choices. Cho says it meaning the end product binds to the promoter region. But in general, it's not the end product that binds to the promoter region. It would be the repressor protein that binds and not usually exactly to the promoter. It's usually again to that nearby operator sequence, but the operator kind of overlaps the promoter. So you could describe it that way. But again, it's usually the repressor protein, not the end product itself that binds to the promoter. So choice A is not correct. Choice. B says it binds to the repressor protein activating it to bind the operator. And that is correct. You generally have your end product that binds the repressor protein and that activates it in a way that it binds to the operator and prevents R N A preliminaries having access to the promoter. In that case, in choice C, it says it binds to the R N A polymerase, preventing it from transcribing the genes. And again, that's not usually the mechanism by which it works. It binds to the repressor, not the R N A plea itself. And then finally, choice D it binds to the operator region preventing R N A polymerase from transcribing the genes while this is close. But it's the repressor protein that binds to the operator region, not the end product itself, the end product tends to bind to the repressor protein. So that's why choice D is not correct. And our correct answer for the way in which an end product of a repressible operon system can function as a repressor. Choice B oops, it binds to the repressor protein activating it to bind to the operator. See you in the next video.

Key Concepts

Repressible Operon

Operon Structure

Gene Functions in Operons

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