In this video, we're going to introduce inducible operons, and so inducible operons are operons themselves that are normally turned off, and when they are turned off the genes will not be expressed. Inducible operons are normally turned off. However, they can be turned on under very specific conditions. When they can be turned on, that means that they can be induced. The conditions where they can be turned on include the presence of what's known as an inducer, which we'll introduce here very shortly. Inducible operons are normally turned off but can be turned on. What happens is an active repressor protein is going to repress transcription under normal conditions. The inducible operon will be normally turned off when there is an active repressor protein repressing transcription. However, the active repressor protein can be inactivated by the inducer molecule. The inducer molecule will bind to the active repressor protein and inactivate the repressor, which will allow for transcription to proceed. In other words, the inducer molecule is going to inactivate the repressor protein. When it inactivates the repressor protein, transcription will be turned on. This is why it's called an inducible operon because it can be induced even though it's normally turned off.

If we take a look at our image down below, we can get a better understanding of an inducible operon in the presence of an inducer molecule. Here, we're showing you the inducible operon, which is very aligned with positive gene regulation because what you can see, from our previous lesson videos when we talked about positive gene regulation, is when you turn a gene on. Over here on the left hand side, what we're showing you is the inducible operon under normal conditions. The inducible operon is turned off. The reason that it's turned off is because an active repressor protein will bind to the operator and block or prevent transcription, block the RNA polymerase and block transcription, so none of these genes will be expressed normally. However, under very specific conditions that include the presence of an inducer molecule, in the presence of this inducer molecule, the inducer molecule will bind to the repressor and cause the repressor to change its shape, change its conformation. The inactive repressor here can no longer bind to the operator. That means that the operator here is going to be free, and the RNA polymerase is capable of binding to the promoter and proceeding with transcription. In the presence of an inducer molecule, the inducible operon can be turned on. You can see here we have our light switch being flipped into the on state. Of course, when transcription is turned on, the mRNA will be made, and, of course, the proteins will follow with translation are undergoing positive gene regulation, which means that they can be turned on, although they're normally off. This here concludes our brief introduction to inducible operons and as we move forward we'll continue to learn more and more about operons and be able to get some practice. So I'll see you all in our next video.