In this video, we're going to talk about the structure of an operon. An operon is defined as a set or a group of prokaryotic genes, usually of related function, that are controlled by a single promoter. Recall from our previous lesson videos when we talked about transcription that the promoter of a gene is going to be just ahead of a gene, a DNA sequence just ahead of the gene where the RNA polymerase will bind. If we take a look at our image down below, notice that our operon is being labeled from this region here over to this region over here. What you'll notice is that the operon contains a group or a set of related genes. And here in our image, the related genes are gene a, gene b, and gene c. Notice that these related genes a, b, and c, are all controlled by a single promoter region, and the promoter region is up here in green. The operon also includes this other yellow region here that's called the operator. The transcription of the operon is regulated by the operator. The operator is a region of DNA. It's a small DNA sequence where regulatory proteins will bind. These regulatory proteins will bind to the operator and affect the RNA polymerase binding to the promoter. Some regulatory proteins will repress or block the RNA polymerase from binding and other regulatory proteins will promote or stimulate the RNA polymerase binding.
Down below, what we're showing you are repressors which are regulatory proteins themselves that will block or inhibit RNA polymerase binding, preventing transcription. And then, of course, activators are going to be regulatory proteins themselves that will actually promote RNA polymerase binding, stimulating transcription. If we take a look at our image down below, again, notice that the operon itself contains an operator, and the operator is going to be the site for the binding of a regulatory protein here. The regulatory protein is going to have its own gene, and the regulatory gene is over here, and the regulatory gene has its own promoter. The promoter for the regulatory gene is here, the regulatory gene is here, the regulatory gene gets transcribed and translated into this regulatory protein. This regulatory protein, when it's active, will bind to the operator, as you see here. Depending on if the regulatory protein is a repressor or an activator, it will either block or promote the RNA polymerase binding. We have the RNA polymerase that will bind to the promoter, and it will not be able to bind if there is a repressor bound. But if there is an activator bound, then the RNA polymerase will be able to bind. Of course, RNA polymerase binding is necessary for transcription. This is really an operon. An operon is going to be, again, a group of related genes like a, b, and c here that are controlled by a single promoter, and transcription of these genes is controlled by this operator region, which will be the site for the regulatory protein binding.
As we move forward in our course, we'll be able to talk more and more about operons and specific types of operons and exactly how they function. But for now this here concludes our introduction to the structure of an operon and we'll be able to get some practice moving forward. So I'll see you all in our next video.