Have you ever thought about what a disaster it would be if the cells in your eyes started producing the same hydrochloric acid that is made by your stomach cells? Your stomach cells produce hydrochloric acid to help break down food, but you definitely don't want that in your eyes. Thank goodness that doesn't happen.
But it's surprising because both your eye cells and your stomach cells contain all of your DNA. Your DNA, all of it, is found in your body cells. But see, the portions that are used to make your body used need to be regulated somehow.
Otherwise, we could end up with something ridiculous, like eye cells producing hydrochloric acid. And that wouldn't just be a waste of resources. That would actually be very difficult to explain to your friends.
You want genes to be regulated, controlled. Remember that genes are made up of DNA. DNA is used to give instructions for the production of proteins in the process of protein synthesis. But an important concept is that there needs to be a method of determining which genes will be turned on and which genes will be turned off.
This is called gene regulation. And there are many ways that genes are regulated. In your human body cells, you can have proteins that can bind to certain gene regions to increase the rate of transcription for the transcription enzyme RNA polymerase. Or you can have proteins decrease transcription to the point that it may not be transcribed at all. This is a form of gene regulation.
Your eye cells don't use the portion of DNA that codes for making hydrochloric acid like your stomach cells do, because there is regulation in your cells to determine which portions of the DNA is used. But we want to shift gears now to talk about a very interesting way of regulating genes that can be sometimes a little challenging to visualize. This particular method is really found in prokaryotes, a few eukaryote exceptions.
It's called an operon. An operon is a f- fancy way of regulating genes and it's usually made up of a few genes that can involve enzymes. Remember that enzymes are proteins with the ability to break down or build up the substances that they act on.
Now let's talk about some key players in an operon so that we can see some gene regulation here. First, RNA polymerase. It's a builder. A builder enzyme actually because RNA polymerase is an enzyme. In biology, a lot of enzymes end in that A-S.
RNA polymerase is needed in order to start transcription. Remember that transcription and translation are steps in protein synthesis. Protein synthesis means to make proteins, enzymes in this case. The thing about RNA polymerase though, it gets a little confusing for RNA polymerase without somewhere to bind. If you watched our DNA replication video, you learned about DNA polymerase and how it had to have a primer to know where to start.
Well, RNA polymerase needs a promoter. A promoter is a sequence of DNA where the RNA polymerase can bind. So you would think, okay, you got your RNA polymerase, you attach it to a promoter, and boom, you make your mRNA, which eventually will be used to make a protein.
But there's this other sequence of DNA called an operator. The operator is a part of the DNA where something called a repressor can bind. The repressor, if bound to the operator...
blocks RNA polymerase and poor RNA polymerase cannot move forward and no mRNA can be made, therefore no proteins. So let's take a look at our setup here. This is an example called a lac operon.
Notice there's a promoter region of the DNA, the operator region of the DNA, and there are three genes here that code for enzymes that help in the process of breaking down lactose. Lactose is a sugar. If lactose sugar is around, bacteria want these enzymes to be made so that they can use them to break down the lactose sugar.
Then they can metabolize it. Fed bacteria are happy bacteria. Here's the repressor.
There's actually a gene here that codes for producing the repressor. See this gene that we call I? It has its own promoter.
Well, this gene codes for the production of the repressor. So why do we need this repressor? Well, it's wasteful to make things that you don't need. If there's no lactose, it wouldn't make sense to start making enzymes.
that work together to break down lactose, it would be a waste. The enzymes would just sit there. So if lactose is not present, then the repressor binds to the operator, and this blocks RNA polymerase.
So mRNA cannot be made, and therefore the proteins, the enzymes in this case, cannot be made. But if lactose is around in the environment, something pretty cool happens. The lactose, remember that's the sugar, binds to the repressor. This is the sugar.
This changes the repressor's conformation. Try as it might, the repressor cannot bind to the operator. RNA polymerase finds its promoter, binds, and transcribes to make the mRNA from the genes on the operon.
That mRNA will be used to make enzymes to break down the lactose sugar. And bacteria like to eat, so that makes them pretty happy. We have to say that we think it's pretty impressive to think about all the gene regulation that occurs in cells.
And if you find it fascinating, know that there are careers that focus on gene regulation and understanding how genes can be turned on and turned off. Because by doing that, we can gain a better understanding of a variety of diseases that have gene influences in the human body. Well, that's it for the Amoeba Sisters, and we remind you to stay curious.