[Caitlin:] Hey Felicia, isn't the alphabet great? [Felicia:] Ahh, it depends. [Felicia:] What do you mean? [Caitlin:] Just 26 letters and you can form enough words to fill a whole dictionary. Words like this. [Caitlin:] A million points for me! [Felicia:] That's okay, because I've got a different kind of play. [Caitlin:] You don't mean... [Felicia:] That's right, A-T- [Caitlin:] C-G. No! [Felicia:] The base pairs of DNA. [Caitlin:] In the next few minutes, we're going to tell you how these four letters make us, us. [Felicia:] And how A-T-C-G are the letters of life. [Caitlin:] Well played. [Felicia:] Welcome to... [BOTH:] DNA Decoded. [MUSIC] [Felicia:] Why are these four letters so important? What is so special about them? [Caitlin:] We'll get to that, but first we need to take a step back and talk about the purpose of DNA. You can think of DNA as a computer code or a program. A computer uses a binary code system -- [Felicia:] That's zeros and ones -- [Caitlin:] Yes, much like a binary code used by a computer to encode an image. [Felicia:] Oh, can it encode an image of a zombie? [Caitlin:] Yes, of course, it can encode an image of an zombie. [Felicia:] Like a George Romero zombie? [Felicia:] That's not a George Romero zombie! That's just a cute clip art. [Caitlin:] Ignore her please. As I was saying, much like a computer program uses binary code to generate this scary zombie, DNA uses a code made up of four letters, or what we call nucleobases -- [Felicia:] A-T-C-G. [Caitlin:] -- to ultimately make proteins. Proteins are the end product of our DNA. They carry out the majority of the work that makes you, you. [Felicia:] You know, Cait, these four letters are not exactly letters at all. They're so much more than that. They are molecules! [Caitlin:] A for Adenine, T for Thymine, C for Cytosine, and G for Guanine. [Felicia:] But you're probably wondering how does all this come together in a DNA molecule? I couldn't sleep last night -- too many zombie movies -- so, I put together this DNA model to show you how the structure of DNA looks like: a double helix. Kind of looks like a twisted ladder. If we unwind the double helix, we can focus on the rungs of the ladder. Each rung is made up of two bases. [Caitlin:] And really, when we say bases, it's a short form for nucleobases. [Felicia:] Two nucleobases come together to create a base pair, which are the rungs of the ladder. There are two simple rules for remembering how the bases come together to form a base pair. A pairs with T. So, if one side of the ladder is an A, the other side will be stuck to a T. [Caitlin:] And C pairs with G. So, if one side of the ladder is a C, the other will be stuck to G. [Caitlin:] These rules are credited to two very famous scientists, Dr James Watson and Dr Francis Crick. That's why we call them Watson-Crick base pairs. [Felicia:] Wait a minute, Cait, I just had a eureka moment. Does that mean if we know the specific base pair sequence on one strand of the DNA, then we automatically know the sequence on the other strand? [Caitlin:] Exactly! Want to try to make some base pairs? Say we have the folowing sequence on a strand of DNA: A-C-C-G-T. And we know that A pairs with T and C pairs with G. That means that the sequence on the second strand is T-G-G-C-A. [Caitlin:] Top marks. [Felicia:] To recap, a base or nucleobase can be A, T, C, or G. Two nucleobases come together to create a Watson-Crick base pair, which are the rungs of the ladder. [Caitlin:] You've got it. And now for the sides of the ladder. These are made up of alternating sugar and phosphate... [Felicia:] Cait, that's way too much information. Let's call it a day, I'm getting hungry. [Caitlin:] Okay, but only if we eat cake. [MUSIC] [Caitlin:] Felicia's not here, so this is my opportunity to nerd out on the hardcore science that she won't let tell you about. I'm going to tell you a bit more about DNA, otherwise known as deoxyribonucleic acid. The proper chemical term for the sugar we've been talking about is ribose. Deoxyribose refers to the sugar in the rails of the later. Remember when we said that the base pairs were linked together by weak bonds? Well, this allows them to come apart easily. The base pairs unzip to make a copy of DNA. On the other hand, the rails of the ladder are held together by very strong bonds. We also mentioned A pairs with T and C pairs with G. That's all for now, Caitlin out. [MUSIC]
