So now that we know from our last lesson video that in the absence of lactose the lac operon is off or inactive, in this video, we're going to talk about the lac operon but in the presence of lactose. And so when lactose is readily available to metabolize in the environment, lactose can actually act as an inducer molecule in the lac operon. And so really it turns out that a derivative of lactose, that's called allolactose, you may or may not be responsible for knowing allolactose, but a derivative of lactose is going to bind and inactivate the repressor protein, lac I. And so if lac I is inactivated, then that means that it will not, it cannot bind to the operator. And if it cannot bind to the operator, that means that RNA polymerase will be allowed to initiate transcription of the lac operon, and so that will turn on the lac operon.
And so if we take a look at our image down below, notice we're saying in the presence of lactose, when lactose is readily available to metabolize, then lac I, the repressor protein, is going to be inactive. And if it's inactive, that's going to allow for lac operon transcription, turning on the lac operon. And so here again in the title, we're saying that the lac operon, we're focusing on the lac operon in the presence of lactose, and so this is our molecule to represent lactose. And so notice over here we have again our lac regulatory gene, lac I, with its own promoter here. And lac I is going to be transcribed and translated into the lac repressor. However, notice that in the presence of lactose, a derivative of lactose will be able to bind to the lac repressor and inactivate the LAC repressor. And so notice that the LAC repressor here has changed its conformation, and now it is no longer able to bind to the LAC operator and block transcription. And so because the inactive lac repressor cannot bind to the operator, this allows RNA polymerase to bind to the lac promoter and initiate transcription of these lac operon genes, lac Z, lac Y, and lac A. And so of course it's going to create an mRNA strand and the mRNA strand is going to have a start codon here for each of the genes within it. And, ultimately, this mRNA is going to be translated. And when it's translated, it's going to be converted into these enzymes, and these enzymes will be able to break down lactose. And so they can go over here and break down lactose and use lactose as an energy source. And so ultimately what we're seeing here is that the lac operon is really only going to be on or active in the presence of lactose when lactose is available, and that allows the genes to be turned on when they are needed.
This here concludes our brief introduction to the lac operon in the presence of lactose, and we'll be able to get some practice applying the concepts that we've learned as we move forward in our course. And then we'll also get to talk about how glucose will also impact the expression of the lac operon. So we'll talk more about that as we move forward. So I'll see you all in our next video.