DNA Discovery

Hi in this video we're gonna be talking about D. N. A. Discovery. So for this I'm just gonna go over a few of the main people and experiments that led to the discovery of D. N. A. As the source of genetic material. So um one thing is that it took a really long time to actually discovered D. N. A. Is the source of genetic material because for a long time protein was the source of um or was thought to be the storage molecule for genetic information. So this is around the 19 hundreds and so they thought it was protein because protein has so many more possibilities. So there are 20 amino acids but only four DNA bases and so bac Because there were 20 amino acids they just thought well you know it has all of this information to store. So it has to be protein but it wasn't. And so it took some experiments to figure out that it wasn't and that DNA was instead um the source. And so one of these main experiments was done by Oswald avery and he showed that DNA was the genetic material of bacteria. And this happened around the 1940s. And so how he did this as he injected mice with two bacteria noninfectious and a dead infectious but the mice became infectious anyway infected. Anyway. And so this actually showed that the nucleic acids were the reason for conferred infectivity. And so I'm going to show you an example of that in just a minute There's another experiment or another group of people. Um these are the Hershey Chase experiments and this show that DNA was the genetic material of viruses in the 1950s. And so how they did this is they took viruses bacterial pages which are bacteria or viruses that infect bacteria and they labeled them with radiation. And so they labeled the protein with one type of radiation and they labeled the D. N. A. With a different type. And so when they infected bacteria with it they said okay well what actually infected the bacteria? Was it the protein that was radioactively labeled or was it the DNA. That was radioactively labeled? And so they found that it was actually the D. N. A. That was being transferred into bacteria and causing the infection. Um So this was really important in finding that the genetic material was D. N. A. And not protein. And then um the final one which I'm going to talk about which I'm you know I'm sure you've heard of before is James Watson and Francis crick and they discovered the D. N. A. Double helix. And this was really crucial in identifying D. N. A. As a source of genetic material because with this structure it provided this really elegant explanation of how genetic information is stored replicate and replicated and inherited in a way where other structures. It wouldn't quite make sense. So that was a really important one. So let's talk a little bit let's go over this avery experiment as just one of the experiments that really led to the DNA. Discovery. So what Oswald Avery did is he injected mice with with viruses. And so um here you have this experiment and he obviously had four different ways. This happened. 1234. So the first one is he infected a live non infectious virus. And so of course the mouse lived because the virus wasn't infectious. Then he um injected the mice with the live infectious virus. And of course the mouse died because it became infected. Then he infected a different set of mouse with a dead infectious. So this is what would be an infection virus if it were life but because it's dead it's not gonna be infectious. And of course the mouse lived because it was because it was dead. Now you can see here that he took 1/4 set of mice and he infected them with two viruses and so he infected them with a dead infectious. So this by itself which we saw here is non effective. The mouse lives and here you have a live non infectious And you saw here that's this one here and the mouse lips so independently these viruses caused the mice to live. But together actually you can see here that the mouse died and so why would two viruses that by themselves were you know completely allowed the allies to live? Why when combined would they call the vows to die? Well they do this because the D. N. A. From the from the dead infectious um has the DNA to be infectious. It's just not live can transfer its D. N. A. Draw this here to a live noninfectious. So because it can transfer this D. N. A. It can make this non infectious bacteria become an infectious one and it'll kill the mouse. So this is the example of the Oswald avery experiment which was one of the main experiments that showed that D. N. A. Was the source of genetic material and not protein. Let's move on.