Nucleic Acids 3

The idea is we just talked about on the last page are more or less encapsulated by one of SHAR gaffes. Rules, which are a Siris of rules about the composition of DNA that were used by Watson and Crick. Tieu help determine DNA structure Now there were a number of different rules Sharga developed. However, we're really just going to focus on the one that deals with the base composition of DNA. And it's more or less summarized by the statement that in a double stranded molecule of DNA, the amount of adding equals the amount of timing and the amount of guanine equals the amount of cytosine. Likewise, the amount of pure ings will be equal to the amount of PIRA meetings. And again, these are the ideas we were just talking about on the previous page. Um, Watson and Crick didn't just use charge offs rules to determine DNA structure, though They also used an X ray crystallography image from Rosalind Franklin pictured right here and the image they used, you can see right next to her was called Photo 51. I love this name. It's like super, um, mysterious sounding right. Like Area 51 photo 51. It's great. And basically what this image showed Watson and Crick is that DNA had a simple structure and it had substitute ants that were about 3.4 angstrom apart. And, of course, those substitutes are the bases we now know about. So, uh, that is an important number two no, guys, 3.4 angstrom za part. Make sure you memorize that. All right, so the structure of DNA that Watson Crick came up with is called a double helix. And the double helix contains two grooves in it, actually, a major groove and a minor groove. And I'm gonna trace those out for use that you can maybe see them a little better here. So the minor groove is this smaller one in this opening right here. And it kind of snakes along this way in the molecule, The major groove, on the other hand. And you can actually, before we go there, you can actually see the minor groove right here. It's this space. The major groove, on the other hand, is this big open area here, and you can see it wraps around the molecule like that, and it's pictured over here as this big open area like that. So the main point of thes grooves is this is how stuff interacts with DNA. It binds into DNA, generally using the major groove, though sometimes the minor groove is used by certain specific proteins. But obviously lots of proteins and enzymes need to bind DNA to carry out gene expression and to regulate gene expression. Now it's important to note that the structural bonds of DNA, all single bonds and that makes the molecule pretty flexible. And if you think about it, uh, the nucleotides air also, with the exception of some double bonds on the basis, of course, and the phosphate groups, the nucleotides are made of many single bonds as well, and this means that they're also quite flexible. And actually, nucleotides can have two confirmations that you can see right here. There is thesis, inform and the anti form. And basically, that is just a flip flop of the base on this single bond right here, right? It can basically kind of flip flop around on that single bond between these positions. However, in uh, in our DNA, the anti form is generally the confirmation seen sin is much less common. Also, that is the worst arrow I've ever drawn in my life, so I'm redrawing it. Boom. Anti form is more common. All right, now let's flip the page.