 Nucleic acids are one of our four classes of biomolecules. We've looked at carbohydrates, we've looked at lipids, now we're going to look at nucleic acids, and we're going to look at proteins in this section as well. So let's get started. Let's do a definition to start with of a nucleic acid. It's a biomolecule. But like all of our biomolecules, it's made of subunits. And so we can almost define it by what it's made of. Made of nucleotides. And there's many different nucleic acids. DNA is an example of a specific nucleic acid. RNA is an example of a specific nucleic acid. And we have different kinds of RNA that, again, that's the category of organic molecule that we're talking about. All of them are made of nucleotides. So I'm going to draw a picture of what a nucleotide is. First of all, my picture is wind-ified. Because this isn't really what it actually looks like. First of all, all nucleic, all nucleotides have, this is a nucleotide right here. The nucleotides have a pentose sugar. Pentose sugar. And a pentose sugar just means there are five carbons in the sugar. Glucose is not a pentose, actually, I think it might. No, it isn't, a pentose sugar because it's C6H1206. So if it has six carbons, it's not a pentose sugar. I'm going to tell you a couple of examples of pentose sugars. One of them is deoxyribose. That's a pentose sugar. Oase often tells you sugar, glucose, fructose, lactose. Another pentose sugar that we're going to look at is ribose. Ah, the plot thickens. So either deoxyribose or ribose are going to make up this pentose sugar in our nucleotide. Owned chemically bound to my pentose sugar in a single nucleotide, we have one phosphate molecule. Just like adenosine triphosphate had three phosphates attached, a single nucleotide has one phosphate attached to it. And then the other thing that all nucleotides have, I don't know why I draw them like this, this is a nitrogen base and it's just a molecule that obviously includes nitrogen. There are multiple different flavors of nitrogen bases. We have, maybe I'll write them all down for you. I'm not sure if there's another time when I'll do that. So let's do, our nitrogen bases could be adenine, thymine, guanine, oops, guanine, cytosine, or uracil. These are our possible nitrogen bases. And we're going to look at their structure a little bit more as we get into, like, what did Watson and Crick discover about this whole thing? Hmm, is there anything else you need to know? If you look at, I'm going to tell you two more things. My pentose sugar, I could actually draw it as a little, like, pentagram, is that a pentagram? Pentagram, I think so. And I'm going to tell you that the phosphate attaches to carbon number five. This is something that you might be, like, going, really? Why do we care about that? Carbon five is the carbon that the phosphate is attached to. And then another important carbon is carbon number three. And that'll become, that's important when we look at the overall structure of the DNA molecule. DNA molecules are made of multiple nucleotides. I'm going to show you what they actually look like from a molecular standpoint. Oh, that was the whole DNA molecule. But take a look at this. These are different flavors of nucleotides. This one is cytosine. You can see here is my phosphate. This is my pentose sugar. And here's my nitrogen base. Same thing over here, nitrogen base. You can see that the guanine has a different structure than the cytosine. The guanine is similar in structure to the adenine. Thymine and cytosine are similar in structure. But these are the basic building blocks that make up any one of our nucleic acids. Let's look now at specifically what the DNA structure, how a DNA molecule is built from these building blocks.