tinywow_video_to_text_65330796.txt

Next class of biological macromolecules is going to be nucleic acids. This is going to be either DNA or RNA, you definitely should know that DNA is deoxyribonucleic acid, RNA is ribonucleic acid, and you should definitely understand what that difference. Why is there a difference between ribonucleic...

Next class of biological macromolecules is going to be nucleic acids. This is going to be either DNA or RNA, you definitely should know that DNA is deoxyribonucleic acid, RNA is ribonucleic acid, and you should definitely understand what that difference. Why is there a difference between ribonucleic acid and deoxyribo nucleic acid? Well, it turns out that the ribo part is that they both involve ribose sugar. In the case of RNA, it's simply just ribose. In the case of DNA, it's deoxyribose, where one of the hydroxyl groups is missing on carbon two, as we'll see. We talk about the difference between a nucleic side and a nucleotide, it turns out these nucleic acids, not only they have sugar, either ribose or deoxyribose, they're also going to have a base, and those nitrogenous bases are what we use abbreviate in genetics as A, C, G, and T, and DNA, but instead of by me there, instead, we get uracil and RNA incorporated instead. We'll talk more about those bases. It turns out we've got the difference between a nucleotide and a nucleotide, and the difference comes down to is do you also have a phosphate group? In addition to your sugar and your nitrogenous base, if you've got phosphate, well then you're nucleotide, and you might have one, two, or three phosphates, so you can have a nucleotide monophosphate, nucleotide diphosphate, nucleotide triphosphate, so on and so forth. So here we can kind of see the structures here, and so I've got an example of a DNA nucleotide in this case, so here we can see that on carbon number two, and if we number those carbons here, let's make this just a little bit bigger for a second, so there's carbon one, two, three, four, and five, so ribose and deoxyribose are five carbon sugars. On carbon two of ribose, you have an OH group right there, on deoxyribose, that's where that OH is missing, and instead of having an OH on an H, you've just got two Hs on carbon two, and that is the difference, and it turns out structurally, that has some pretty profound implications, so it turns out that having no OH right there actually makes DNA nucleotides more stable than RNA nucleotides, it also means that they're much more likely to form a double helix, which is why we typically have DNA existing as a double helix, but RNA might have small, you know, localized regions of double helix and stuff like that, but most of the time we say that the RNA structure is single-stranded, instead not double-stranded. The bases, so we'll talk a little bit more about those bases, so the base that's attached here again, we said like ACG&T for DNA or ACG&U for RNA, those can be divided into two classes, purines and pyrimidines, they are nitrogenous bases, lots of nichons in both, so and you should kind of recognize these two classes, purines and pyrimidines, and which of the bases belong in each class, so you'll notice that purines, the smaller name has the larger structure, they're aromatic, they've got two rings for the purines, whereas the pyrimidines are aromatic with just a single ring, and so purines have the shorter name and the larger structure, pyrimidines have the larger name but the smaller structure, so you might also memorize that cytosine, uracil, and thymine, cut the pie, if you will, so cytosine, uracil, and thymine are your pyrimidines, if you will, and that makes therefore adding and bonding your purines, and you should know which is which. So now we'll get to the polymer, we'll talk about the monomer, so and DNA, that's going to be that DNA double helix that you're probably somewhat well acquainted with and stuff like that, so you get two separate strands of polymer here in this case of nucleic acids bonded together, and these two separate strands are held together not by any covalent bonds, but by largely hydrogen bonding, most students are familiar with, so, but it turns out also there's something called base stacking involved as well, and you've got, again, all these nitrogenous bases, that's where the hydrogen bonding is occurring in the interior there, so well they're all aromatic, and so they have pi-molecular orbital systems that actually, in successive base pairs, actually overlap, you might have some pi systems going on here, but then you got some down in the next set as well, and you get some overlap right here, we call that base stacking, so not the most important thing in the world that I want to make you realize that it's not just hydrogen bonding, although that's probably the most important part, but you've also got this base stacking going on as well, so we sometimes talk about what are called intercalating agents, and these intercalating agents can squeeze in between the base pairs right in this region, they're usually very flat planar structures, and often aromatic, so that they can kind of take the place of the base stacking here, and these intercalating agents often lead to mutations in the disorder replication. Alright, let's take a look, one more thing real quick, actually, so a most common form of DNA structures, what we call B-form DNA, so it's a right-handed helix, and most of the time DNA, when we talk about it's structure, we'll be usually referring to that B-form. It turns out there's also an A-form, it's also right-handed, it's a little bit elongated and stuff like that, and then there's a much rare form called Z-form that is left-handed, and again it's not like a whole DNA strand is going to be in this Z-form or anything like that, what often happens is when you unwind DNA, so it puts a strain on the structure, and sometimes very localized regions right around where it's unwinding might be existing at Z-form temporarily and things of its sort, so, but you should know B-form, most common form, right-handed helix, Z-form, not so common, left-handed A-form, you might not even see, but also right-handed. Some key words here, we're going to find out these strands are anti-parallel and complementary, that's going to be a little easier to see on the next slide, and we're also going to talk about this phosphodiester bond as well that holds the back bones together, let's take a look. Alright, so we'll look at a small segment here of the DNA double helix, we've got one strand, one strand on the left, one strand on the right, and we can see the hydrogen bonding that's going on that's holding them together, so, and it turns out, so I definitely want to be familiar with the base pairs that form, you're always going to have one purine interacting with one pyrimidine, so, and as a result, it turns out that adding always acts with thiamine in DNA structure, whereas guanine and cytosine always interact with each other, and so, we've got the AT-base pair and the GC-base pair, and if you look, definitely should know that the AT-base pair is held together by two hydrogen bonds, whereas the GC-base pair is stronger being held together by three hydrogen bonds, and so, if you look at regions of the DNA biologically, we might want to unwind it like we're about to do replication or transcription or something like that, but you've got to unwind the DNA to do those processes, and you'll often find that they are AT-rich, like the top-top box, T-A-T-A, they call it the top-top box because it's rich in AT-base pairs, and good thing because it makes it easier to unwind being, again, held together by fewer hydrogen bonds, you also know that these are anti-parallel, so, if we look at carbon 5 here, and then on the other side is carbon, there's 4, there's 3, and we would say this one's in the 5 prime to 3 prime direction, so, and then you've got this phosphodiester backbone holding one nucleotide to another, so if I said, you know, what kind of bond holds amino acid together protein, you should say peptide bonds, which are amides, if I say what kind of bonds hold the nucleic acids together in DNA, you should say phosphodiester bonds or phosphodiester linkages, if I say what kind of bonds hold together the monosaccharides in the sugar, you should say glycosidic bonds, so I want to keep all these classes straight in your head here, so, if you notice, we've got 5 prime to 3 prime running in this direction on this strand, but in the opposite strand is running the opposite direction, and that's what we're meant as anti-parallel, and at DNA double helix, the individual strands of the helix run anti-parallel to each other, cool, this normal pattern of hydrogen bonding, if I didn't mention it, it's called Watson Crick base pairing, so, and that's pretty much what you've got to know, if you took a biochemistry class, you might have heard, like, a hook seam base pairing and things of a sort that's a little less common, and could lead to mutations, not going there, just Watson Crick base pairing, AT base pairs, GC base pairs, 200 bonds, 300 bonds, it's good to go. One last thing, when we talk about the strands being anti-parallel on the last slide, we also said they were complementary, and complementary in terms of base pairing, every time you see an aden in one strand, you're going to see a thymine on the other, because of that AT base pair, this is where the hydrogen bonding conform, so it turns out that, again, you're always going to have one purine and one pyrimidine, and it's always going to be A with T and G with C, there's no A, you know, AC base pairs or GT base pairs, and I can notice it's also going to always one purine with one pyrimidine, and would have to be that way if you kind of keep this kind of thing about logically, otherwise, how long this region is, if you had, you know, two pyrimidines, it'd be shorter, narrower, if you had two purines, it would be wider and stuff like this, but as long as you always have one purine and one pyrimidine, it's going to have a set with all the way up the double helix. Cool, so anti-parallel and complementary.