In this video, we're going to introduce repressible operons. A repressible operon is an operon that is normally turned on, and its genes are normally expressed. However, it is repressible because it can be turned off, or repressed under the right conditions, which includes having an active repressor protein. It's important to note that the inactive repressor protein cannot repress transcription without a corepressor molecule. The corepressor, a small molecule itself, will bind to the repressor, forming an active repressor protein. In other words, the corepressor molecule activates the repressor protein so that transcription is turned off when there is an active repressor protein.

Let's take a look at the image below to get a better understanding of a repressible operon. A repressible operon aligns with negative gene regulation, as the gene can be turned off. Under normal conditions, they are typically turned on. You will note that when it is normally turned on, the RNA polymerase can bind and transcribe, forming an mRNA. The mRNA is then translated into the gene products. The genes are being expressed because the repressor is in an inactive form. This inactive repressor protein requires a corepressor to bind. Notice that under specific conditions, if there is a corepressor molecule, represented by a little red molecule, the little red corepressor can bind to the inactive repressor to form an active repressor molecule. The active repressor can then bind to the operator to block, inhibit, or prevent transcription, turning off the gene and the operons.

Repressible operons are normally turned on but can be turned off under the right conditions, which include having a corepressor molecule present. Notice the image of the light switch being turned off, illustrating what repressible operons are capable of doing. This concludes our brief introduction to repressible operons, and we'll be able to get some practice applying these concepts as we move forward. I'll see you all in our next video.