Operons

Today in class, we talked about operons. An operon is a unit made up of a bunch of genes. These genes regulate other genes responsible for protein synthesis. We were shown two examples of operons today. The first one had to do with tryptophan, a type of amino acid. This operon is on, meaning it is repressible. This operon has to be stopped. There is a regulatory gene in the front of this operon, and it has to be read by RNA polymerase. Next, an mRNA is created which then creates a repressor. This repressor is inactive; therefore, the RNA polymerase can go down the system of genes and read them. They create the polypeptides that make up the enzymes for tryptophan synthesis. When there is enough tryptophan, it can go into the repressor and activate it, which can then lock the system of genes. Furthermore, no RNA is made. The repressor is like a wall blocking the RNA from going through, and because of this more tryptophan cannot be made.

We also learned about an inducible operon, meaning it is off. This a lactose operon. Everything is pretty much the same as the tryptophan one. There is a repressor, a promoter, and an operator. One difference, however, is that the represoor starts off active, obviously, because it starts off stopped. So no RNA can be made due to the "wall." This happens when lactose is not present. When lactose is present, it is inducible. Therefore, repressor is inactive, the operon is on, and transcription occurs. In other words, RNA polymerase can pass through and RNA is made. 

All of this connects to a lab we did a few days ago. The lab was on pGLO. In our lab, we had four different containers with bacteria, but only the container containing arabinase was able to glow. This is because of the arabinose (sugar) which turns on the gene, allowing the RNA polymerase passage and causing it the bacteria to glow.