Have you ever wondered why it is that children usually end up looking like their parents? Hi, I'm Janice Crenetti. I'm here to talk to you today about what are the four nitrogenous bases of DNA? I've been teaching biology and environmental science in high school for over twenty years, and I've spent a lot of those years teaching my students about DNA, and why it's so important to understand. I have a DNA molecule here up on the screen. DNA is extremely important to understand from a scientific perspective any time you're talking about the human body, because DNA is makes us what makes us who we are. It's what determines our eye color and our hair color; whether or not we're prone to certain diseases, and DNA is found inside the nucleus of just about every single cell in your body, so there's a whole lot of DNA inside of you. Well, if you could break a DNA molecule down, I have a smaller version right here. In a cell it's actually twisted up like this in a double helix, but if you were to untwist it you would see that DNA sort of looks like a ladder, and you'll notice that in my ladder I have four different colored rungs. Well, each of these different colored rungs represents a different DNA base. You have adenine, thymine, cytosine, and guanine. Now, one of the reasons that DNA actually works, the reason it's able to replicate and reproduce more of itself is that it's got some rules. The adenine always pairs with the thymine, and the cytosine always pairs with the guanine. For whatever reason that's how DNA works. It's all based on connecting with these hydrogen molecules. So, DNA can replicate itself over, and over, and over again because of those base pairs. Now two of those, adenine and guanine are considered to be purines, where the others, cytosine and thymine are considered to be pyrimidines, and basically, that means that they have a different chemical makeup. The purines are a little bit larger. They have two carbon-nitrogen rings in their molecule as opposed to only one. All of that complicated material comes together to make a DNA helix, and all the DNA helixes in your body make you who you are. So, I'm Janice Crenetti, and this is what are the four nitrogenous bases of DNA.
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