In this video, we're going to talk about the tryptophan operon specifically in the presence of tryptophan. And so when tryptophan, this amino acid, is really abundant and prevalent, and found in high levels in the environment, then the cell does not really have a need to synthesize its own tryptophan. And so the tryptophan operon, which has genes for synthesizing its own tryptophan, is going to be inactive when there is plenty of tryptophan that is abundant in the environment. And so what happens is tryptophan is going to act as a co-repressor to the repressor protein. And so the co-repressor, tryptophan, is going to bind to and activate the TRP repressor protein. And so if we take a look at our image down below, we can see that cellular tryptophan is going to co-repress the trp operon when it's readily abundant for the cell. And so we're specifically looking at the trp operon in the presence of tryptophan. And so when tryptophan is really abundant and prevalent, then the cell has no need to synthesize its own tryptophan and so it needs to shut down the TRP operon. And so this is how it works. The TRP regulatory gene, which encodes the TRP repressor, has its own promoter, it's going to be transcribed and translated into an inactive TRP repressor. The inactive TRP repressor is only going to be activated in the presence of tryptophan. And so when tryptophan is really, really abundant, then there's going to be tryptophan available to bind to the inactive TRP repressor, and tryptophan is going to act as the co-repressor here. So the tryptophan co-repressor, and that is going to form an active TRP repressor. And notice the active TRP repressor is capable of binding to the TRP operator, and when it's bound to the TRP operator, it's going to block and inhibit transcription, turning off the TRP operon. And so it's going to prevent the RNA polymerase from binding to the promoter and proceeding with transcription. And so, basically, what we're seeing here is, again, when the TRP operon is in the presence of tryptophan, when tryptophan is readily available, then the cell has no need to create its own tryptophan, and so it's going to shut down the trp operon through this mechanism where tryptophan acts as a co-repressor. And so this here concludes our brief introduction to what happens to the tryptophan operon in the presence of tryptophan. And so moving forward, we'll be able to talk about the tryptophan operon in the absence of tryptophan. So I'll see you all in that video.