Chargaff's Rules

in this video, we're going to introduce char gaffes, roles and so way Back in the early 19 fifties, a scientist named Irwin Char gaffe made two very important discoveries related to DNA, and we've got these two very important discoveries number down below number one and number two. And so the first very important discovery that char gaffe made was that DNA based composition actually varies amongst different species, and so different species of organisms will have different DNA composition in different percentages of basis. Nitrogenous spaces add means thigh means side of scenes and guana scenes, A's T, CS and GS. Now, the second very important discovery that charge have made was that for each of these different species that he looked at, he noticed that the percentage of A's and T bases or adding and timing nitrogenous bases were roughly equal to each other, as were the percentages of C's and G's or GS and CS. And so today we know that the percentage of A's and T bases are roughly equal because we know that in the structure of DNA, A's are complementary base pairing with tease on opposite strands and the percentage of GS and CS are gonna be roughly equal again because GS will base pair with seize on opposite strands. However, back in this time in the early 19 fifties, the structure of DNA was unknown. They did not know the structure of DNA, and so this important information here was critical because it helped to reveal the structure of DNA later. And so, if we take a look at our example down below, we're showing you a little snippet of some of char gaffes data. And so what you'll notice is that we've got this table here of the DNA composition in different species, and we've got the species over here on the left hand side and then the percent composition of the DNA in terms of the percentage of Adnan's demeans guana scene inside a scene or eighties GS and CS in each of the species. And so what you'll notice is that homo SAPIENs humans, um, they have a very specific percentage of, uh in composition of DNA, and that varies from, uh, the S Creek E. Coli, which has a different percentage of bases, a different composition of basis. And so the very first, uh, discovery, that char gaffe made was just that. Hey, different species are going to vary in their DNA based composition. And then the second thing that he noticed again is that it doesn't matter which species you look at, the percentage of A's and tease air roughly equal, and the percentage of GS and CS are roughly equal. And so again, if we take a look at humans, homo SAPIENs or humans, the percentage of A is approximately equal to the percentage of tea. So they're roughly in the 31% ballpark, and the percentage of G S is roughly equal to the percentage of sees their roughly in the 19 ish, 18 ish percent ballpark range. And again, it doesn't matter which species you look at again. The percentage of A's and tease air gonna be roughly equal, and the percentage of GS and CS they're gonna be roughly equal. And so that is really what this second important discovery is referring to. Now, the reason that these percentages are not exactly the same is because of limitations and char gaffes techniques that he was using. And so the reason why the A's is not exactly equal to tease again has to do with just some limitations in his techniques. But this was very, very important information to help reveal the structure of DNA. And so this year concludes our introduction to char gaffes rules these two discoveries here, and we'll be able to get some practice applying these concepts as we move forward in our course, So I'll see you all in our next video.