Practice - Nucleic Acids 1

hi in these videos will be going over questions similar to those that you'll see on your biochemistry exam. Three. Before each question, you should actually pause the video and try to answer it yourself. Let's begin by looking at some questions relating to nucleic acids. And again, you should pause the video now and try to answer Question one on your own. The answer to question one is e pure ings have two rings, while pyre imagenes have one ring. But pure rings and pie remedies actually share a ring. And that is this six member ID ring right here that contains two nitrogen ins. And in the case of pure Eanes, this is actually fused to a five member ID ring that contains two nitrogen ins, and you can see it's conjugated, and the numbering scheme is like I'm drawing here, and it's here at the nine position where the base will actually be linked to the one prime carbon of whatever sugar is being used, whether it's ribose or deoxyribonucleic and pyre. Emma Deans again. They're just that six remembered ring with the two nitrogen zones like that, and they're numbered the same way. Oops, number the same way. The difference is there actually attached at the one position to the one prime carbon on the sugar. And while pure ings come in on Lee, two flavors add ning and guanine pi remedies Come in three Cytisine, You're a cell and diamond and nice way to remember this is with the pneumonic pure, as in pure ing's as gold and cut pi as in pirate meetings. Pretty easy to remember. All right. Question number two The answer to question number two is E The units are linked together between the three prime hydro excell of one sugar. So I'm here's the three prime group, and that is where you're gonna have your fost bodi Esther Bond and that attaches to the five prime carbon of this other sugar. All right, Uh, just thio take a look at the wrong answer choices here. Phosphate. Ester bonds don't link bases. Those air linked by hydrogen bonds, of course. Um, Onley RNA is susceptible to alkaline hydraulics, ISS. And that is of course, because of the presence of that to prime hydro axle. In addition to three prime, I draw axle uncharged at neutral Ph. No way. Phosphates, guys. Negative charge guys and form between the planer rings of the nucleotide bases again. No. The nucleotide bases have thes hydrophobic stacking forces, but no phosphor digester bonds between them. All right, Question number three. The answer to question number three is actually de and we kind of briefly touched on this idea in the question above. And the reason that D is wrong is because again, RNA has that to prime hydroxyl group right next to that three prime hydroxyl group, and that three prime hydroxyl group will participate in the phosphor. Oh, digester bonds, right. I'm kind of abbreviating the structures here, not trying to draw the whole thing. And basically, in alkaline conditions, you can get a reaction that leads Thio cycle ization. And what you wind up with is this. So here's our two prime. Here's our three prime and you have a cyclist molecule in but not drawing the whole thing out here, uh, again. But all I'm trying to show is that you get cycle ization there. You don't get it between three prime and five prime position. And this structure this three to cyclist molecule, this actually breaks down to equal amounts of the three prime nucleotide monta phosphate and the two prime nucleotide Monta phosphate. So you can get be. You can get a 23 cyclist version. Or you can get a to prime non cyclist version just a two prime nucleoside Monta phosphate just like an A and C. Or you could get a three prime nucleotide monta phosphate because the cyclic structure again well, break down into equal amounts of the three Prime, the two prime. All right, so question number four this question you might have noticed, actually has to correct answer choices B and D. And the reason for this is if we take a look at our molecule, take a look at our piece of DNA here. That p right here. That means this is the five prime end. And that means that a is on the three prime end. Now the three prime end again. It always ends in an O. H, right? Just like we saw up here before and in previous examples, the three prime end of our molecule is always gonna have a no h group. And that's actually the site of the reaction with the new nucleotide. That's where you'd actually attach a nuclear tied triphosphate. Right? Anyhoo, uh, in addition to that, it's always convention. That DNA is written from the five prime ends Thio the three prime end. Um, this p is just sort of confirming that this is the five prime end. If you count, it's actually six phosphates, just in case you looked at that and no, this you can't really say this violates shar graphs rules, because paragraphs rules are pertaining to double stranded DNA. And, um, you wouldn't have ah, phosphate on the three prime end because phosphate is on the five prime end and the hydroxyl is on three prime end. All right, moving on to question number five. And the answer to question number five is D roughly plainer. Nucleic acids. Bases are roughly plainer in the structure. It kind of looks something like this. I mean bare with my drawing here. But if we imagine these circles I'm drawing as the nucleic acids bases, they basically sit parallel to each other. So if we were, like, you know, looking down on it, be like one on top of the other, more or less. Right? So anyways, they are roughly plainer, kind of lay flat and they stack on each other. Anyhoo, taking a look at the wrong answer choices. Proteins absorb UV light 280 nanometers. Nucleic acid bases absorb it at 260 nanometers, so jump out of the image. Here to 80 is proteins. They're not all the same size, right. There are two ring varieties and three ring varieties, as we just saw. And that's actually pretty important because if you noticed, pure Eanes are always paired with pie remedy ins and that keeps this with the width of the DNA molecule. Uniforms Pretty cool and pattern you might have noticed is that in biological systems, shape is a very important thing. Shape is often used to convey information and in order for molecules to interact, so having a uniformed with allows ourselves thio. Look for problems in DNA when the you know if the width becomes non uniformed. If you have appearing bound to appearing or a pyre emitting bound to a pyre emitting, it'll be able to tell because the width of the DNA molecule change. Um, and lastly E. I mean, as we just said, hearings always pair thio pie remedies, and furthermore, you always have a hearing t or you if it's RNA and see always pairing with G and, of course, anti form to hydrogen bonds. CNG form three hydrogen bonds. All right, let's flip the page.