Detailed DNA Structure

by Jason Amores Sumpter
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in this video, we're going to talk a little bit more about the detailed DNA structure. And so first, it's helpful to recall the information that we covered about DNA in our previous lesson videos where we first introduced DNA. And so if you don't know anything about DNA structure, then please be sure to go back and check out those older videos on DNA before continuing here. Now, that being said, recall from those older videos that DNA actually consists of two strands of nucleotide monomers or thes nucleotide building blocks that air repetitive Lee linked together. And so, if you take a look at our image down below notice that were actually showing you three different representations of the DNA molecule we've got one representation of the DNA molecule over here, another representation of DNA here in the middle and a third representation of the DNA molecule over here on the right. And so previously in our previous lesson videos, we had shown that DNA forms a double helix where there are two strands one strand there and another strand here that are wrapped around each other and twisted upon each other to create a double helix is twisting ladder type formation. But if you were to take this DNA double helix and you were toe untwist the DNA double helix so that it's ah, straight formation, it would look something like what you see here. And then if you were to zoom into this structure, then you would get this image right here, a more detailed view of the DNA molecule. And again, what you would notice is that the DNA molecule consists of these nucleotides that air repetitive Lee linked together. So here is one nucleotide Uh, this is one nucleotide here. This is another nucleotide here. Here is another nucleotide. And so these nucleotides are just repetitive Lee linked together to create a DNA strand. And so we have to DNA strands. Here we have one DNA strand right here on and then we have a second DNA strand over here. And so notice that these two DNA strands are both made up of nucleotides and they're connected to each other via these hydrogen bonds that form between the nitrogenous basis. And so here we can label these dotted lines as hpe bonds or hydrogen bonds that form between the two strands and that connect and keep the two strands held together. Now recall from our previous lesson videos that a single nucleotide consists of three components. It consists of a phosphate group, a five carbon sugar and a nitrogenous base. Either add ning guanine timing or cytosine abbreviated as a G, T or C, and also again recall that these two DNA strands are anti parallel with respect to each other, which means that they go in opposite directions in terms of their five prime and three prime ends. And so you can see that this strand over here on the left is going from five prime to three prime top to bottom. However, this other strand over here on the right is going from five prime to three prime in the opposite direction from bottom to top. And so the DNA strands are going to be anti parallel. And when you compare the five prime into the three prime end, which you'll notice is that at the five prime in of each Strand is a free phosphate group, and at the three prime end of each strand is a free hydroxyl group. And so what you'll note is that when we take a look at the five prime end again. Over here there is a free phosphate group or a phosphate group that is not linked to another nucleotide, whereas this new phosphate group is not free because it's attached here to to, uh, nucleotides. But this is a free phosphate group and notice that both five prime ends have a free phosphate group and then notice again at the three prime end. You'll have a free hydroxyl group or free O H group, and that applies for both three prime ends. And so what you'll notice is that, uh, here comparing the same sides of the two strands that they are chemically different. One has a free phosphate group, and one has a free hydroxyl group. And so that's why it's important to keep in mind the directionality of these DNA strands in terms of their five prime and three prime ends. And that will be very important as we move forward in our course and talk about DNA replication. Uh, now what you'll notice here is that, uh, the nitrogenous bases are kind of towards the middle of the DNA molecule, and on the perimeter of the molecule is the sugar phosphate backbone, and they call it the sugar phosphate backbone because it's a repetitive repeat of sugar, phosphate, sugar, phosphate group sugar, phosphate group, sugar, phosphate group and so on. And so DNA molecules will have a sugar phosphate backbone. And that's why we represent that sugar phosphate backbone here using these blue lines. And so this here concludes our brief introduction to some of the detail DNA structure, and we'll be able to get some practice applying these concepts that we've learned as we move forward in our course, So I'll see you all in our next video.