In this video, we're going to complete the table that you see down below as we review inducible versus repressible operons. And so notice that here in this row with the greenish background we're focusing on inducible operons, and then down below in this row with the pinkish background, we're focusing on repressible operons. And so recall from our previous lesson videos of inducible operons that they are normally turned off, which means that they will not be transcribed normally. However, these inducible operons can be turned on, and that is why they are called inducible operons because they can be induced. Now, the repressor protein is normally going to be active with inducible operons, and, of course, the repressor protein is going to repress transcription. And because the repressor protein is normally active, it will be normally repressing transcription to turn off transcription normally. However, under the right conditions, when the regulatory molecule is present, specifically the inducer is present, this little circle right here, the inducer will bind to the repressor protein and inactivate the repressor protein. And so we have here an inactivated repressor protein. The effect of the regulatory molecule, the effect of the inducer is to inactivate the repressor protein. And, of course, inactivating the repressor protein is going to allow for transcription to proceed, and so transcription will regulatory molecule inducer. And so, an example of an inducible operon is actually the lac operon, which we're going to talk more details about as we move forward in our course.
Now, of course, recall from our previous lesson videos of repressible operons that they are pretty much the exact opposite of inducible operons. And so they're actually normally turned on. Their gene expression is normally on, and so transcription is usually occurring with these repressible operons. However, under the right conditions, repressible operons can be turned off or they can be repressed. And that's why they're called repressible operons, because they can be turned off or repressed. Now, of course, the repressor protein is normally going to be inactive with operon. And in the inactive state, the repressor protein will not be able to repress transcription, and so transcription will be able to be on. However, in the presence of the regulatory molecule, which in this case is actually going to be a corepressor, this little red circle here. The co repressor will bind to the inactive repressor protein to activate the repressor protein. And so the effect of this regulatory molecule, the effect of the corepressor, is to lead to an activated repressor protein. And so notice that the activated repressor protein is now able to bind to the operator, and that will repress or block transcription, and so transcription will be turned off. And so notice, that an example of a repressible operon is going to be the trp operon, which we're going to talk more details about as we move forward in our course. But for now, this here concludes our review of inducible versus repressible operons, and we'll be able to get some practice as we move forward. So I'll see you all in our next video.