Hi. In this video, we're going to be talking about induced mutations. So induced mutations are mutations that are induced. These typically occur in a laboratory setting, and we typically call this mutagenesis, which is some type of creation of mutations in a laboratory or potentially just in the environment, but it's usually caused by some type of chemical or mutagen that causes the mutation. So there's a few different ones that I want to mention. The first is base analogs. These are chemicals that resemble bases, and so, but aren't bases, so they don't make the right base pairs, they should. So if you put a base analog into cells or into, you know, an organism, then that base analog is going to come in, it's going to fill the place of these bases, but it's not going to make the proper base pairs. These add an alkyl group onto the bases, and this also alters the base affinities, meaning that those bases are not going to bind to the things that they normally would, and generally, this results in transitions. We have intercalating agents, and these are chemicals that wedge between the DNA bases, and they actually cause helix distortions. Now when the helix is distorted, the polymerases and things that bind on to it, usually can't overcome that distortion. They're like, it makes it like a hill, and they can't cross over the hill, and so this ends up generally blocking DNA replication and repair, and this can actually result in pretty severe cell death. So these are big agents, and then finally we have base damage, and these are damages to the bases that prevent base pairings. So UV light, for instance, causes dimers between pyrimidine bases, and radiation, like gamma rays, X-rays, etcetera, can cause damage by creating things called free radicals, which you may have seen on your grape juice or something. But free radicals are essentially these chemicals that are fairly harmful because they go around taking electrons and protons essentially from other chemicals, and so ionizing radiation causes a lot of these chemicals and that can go to the DNA and damage it pretty severely. So here's an example of an intercalating agent, which is here, you can see that it's binding to this DNA where the sugar backbone is here, and these are the bases, and it's binding here. Now if you're a polymerase and you're trying to replicate or transcribe, you're going this way, you're going to get stuck here. This is kind of a roadblock, you can't keep going, and that obviously is going to result in pretty severe mutations, and even potentially cell death. So there's a certain test that scientists use called the Ames test, and this tests various chemicals for their ability to cause mutation. Now you may, you know, we hear all the time, oh, beef or, I don't know, sunscreen or whatever these chemicals cause cancer, and so these tests are these sort of claims are based kind of loosely on the Ames test, where bacteria are exposed to these chemicals and we see, well, does it mutagenize them? And so, many different ways to do this, but it is important. It's not just putting these chemicals with bacteria, because a lot of times when we eat things, that has to be digested. And when it's digested, there's a lot of different enzymes that can break those chemicals down into something that wasn't originally harmful when you consumed it, but is now harmful once it's inside the body. So to test that, you can use the same test, but what they do is they actually take rat liver extracts, which have a variety of proteins, which can break down these chemicals and sort of incubate them or let them sit with those chemicals, and the rat liver extracts will break those chemicals down into whatever they would break down to inside the body. Then, you can take those broken down chemicals and expose them to bacteria. And you do the same thing, you look for mutations. And there's a lot of different ways that scientists can look for how bacteria are mutated, but essentially that's how the Ames test works. So with that, let's now move on.
17. Mutation, Repair, and Recombination
Induced Mutations
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