![]() ![]() ![]() Now the reason why we tend to draw them deprotonated is they're so acidic that if you put them in a neutral solution, they're going to be deprotonated. But even more, the reason why we call it an acid is the phosphate groups, when they're protonated, are acids. And that's what actually forms the rungs of the ladder when these complimentary nitrogenous bases form these hydrogen bonds with each other. Now, a lot of people ask, "Well, if you have these nitrogenous bases here, "why is DNA called an acid?" Why is it called an acid?" Well the first thing is that the basic properties of the nitrogenous base are offset to a good degree based on the fact that they're able to hydrogen bond with each other. The nitrogens have an extra lone pair that can be used up under the right conditions to potentially sop up more hydrogen protons. And the reason why we call them nitrogenous bases, I actually forgot to talk about it in the last videos, is that these nitrogens are really electronegative and they can take up more hydrogen protons. These are the complementary nitrogenous bases. And what links them, you can think of them as the rungs on the ladder. So the phosphate and then you have the sugars in between the phosphates. So on the other strand it's also going to look like this. So we have a sugar there and then you have the sugar there as well. Where we have phosphate with a sugar then another phosphate then a sugar then another phosphate. And you see the same thing on the other strand as well. So you have the phosphates on that end and then you have the sugars. Oops, let me just draw all the phosphates ahead of time. And so I could draw the strand something like this. A phosphate group and then you have a sugar. In the video on the molecular structure of DNA we saw that DNA is typically made up of two strands where the backbone of each of the strands is made up of phosphate alternating between a- Do some different colors.
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