The CAP binding site in the lac promoter is the location of positive regulation of gene expression for the operon. Identify what binds at this site to produce positive regulation, under what circumstances binding occurs, and how binding exerts a positive effect.

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Hi, everyone. Welcome back. Let's look at our next question. It says lac operon is an inducible operon in which the presence of lactose induces the transcription of structural genes. Which of the following statements regarding the regulation of black operon is true choice. A in the absence of lactose, the repressor protein binds to the promoter region due to which R N A polymerase cannot proceed with transcription. Choice B in the presence of lactose, the repressor protein binds to the operator region and thus R N A polymerase proceeds with the transcription choice C in the presence of lactose. The lactose binds to the repressor protein due to which the repressor cannot bind to the operator region. And thus R N A polymerase proceeds with the transcription or choice D all of the above. So let's look at these answer choices to find the true statement. Remembering that we do have that choice. D meaning that all of them could be true. Well, choice is telling us in the absence of lactose, the repressor protein binds to the promoter region. Well, this is not correct because the repressor protein does not bind the promoter region but to the operator that is the repressor protein binding site. So choice A is not correct and therefore trustee. All the above is not our answer. Choice. Choice B says in the presence of lactose, the repressor protein binds to the operator region and thus R N A polymerase proceeds with transcription. Well, this time, it's got the correct binding site for the repressor protein. It does bind to the operator but it does not only in the absence of lactose. When lactose is present, then the repressor is released from its binding site on the operator allowing R N A polymer to proceed with the transcription. So choice B is not correct. And finally, we have choice C in the presence of lactose, the lactose binds the repressor protein due to which the repressor cannot bind to the operator region. And thus R N A polymerase proceeds with the transcription. And this is correct when that, when that lack repressor is prevented from binding to the operator region, it frees up the promoter region. When the lacer pressure is bound, it blocks the promoter and a plume can't get in in the presence of lactose that lactose bound to the repressor protein releases it from its binding site. Now R N A polymerase can come in bind to the promoter and start transcription of the genes. So which of the following statements regarding the regulation of la operant is true. Choice C in the presence of lactose, the lactose binds to the repressor protein due to which the repressor cannot bind to the operator region. And thus the R N A polymerase proceeds with the transcription. See you in the next video.

The CAP binding site in the lac promoter is the location of positive regulation of gene expression for the operon. Identify what binds at this site to produce positive regulation, under what circumstances binding occurs, and how binding exerts a positive effect.

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Key Concepts

CAP Protein

cAMP Levels

Positive Regulation