in this video, we're gonna begin distinguishing between anti parallel and parallel beta sheets. Now you might be wondering why talk about anti parallel beta sheets before we talk about parallel beta sheets? Well, it turns out that the anti parallel beta sheets are actually easier than the parallel beta sheets. So we'll talk about the easy stuff first, and then we'll talk about the harder stuff later. And so, with the anti parallel beta sheets, it turns out that the beta strands are gonna be aligned in opposite directions in terms of their N N C terminal ends. And the rise per residue for an anti parallel beta sheet is to no surprise, 3.5 angstrom. Since we said in our previous lesson videos that beta sheets have a rise per residue of 3.5 angstrom and so down below. In our example, it's pretty clear to see that this image on the left here is an anti parallel beta sheet, and so we can see that we have a single poly peptide chain that's all connected to one another. And these arrows here represent beta strands and the beta strands that are adjacent toe one another right next to another are pointing in opposite directions. And so when they're pointing in opposite directions in terms of their end in C terminal ends that identifies them as being anti parallel beta sheets. And so we know that the arrows are pointing towards their C terminal end because this is the beginning of the chain. This is the end terminal end, and the arrows pointing towards the C terminal end are gonna be, uh, make this the C terminal end over here and again because this is one continuous poly peptide chain that makes this an intra chain anti parallel beta sheet and so moving on to the parallel beta sheets. In contrast, the beta strands are actually aligned in the same direction in terms of their n and C terminal ends instead of the opposite direction. And the rise per residue for ah, parallel beta sheet is actually a little bit more condensed. It's three to angstrom. And so, uh, even though 3.2 angstrom is a little bit more condensed, it's still in comparison to an Alfa Helix. Ah, lot Mawr extended because an Alfa helix has a rise per residue of 1.5 Angstrom. So that's really, really condensed. 3.2 Angstrom is all very extended in comparison to the Alfa Helix. It's just that this anti parallel beta sheet is a little bit mawr extended than the parallel beta sheet. So something interesting to keep in mind and so down below on the right, we have an image of the parallel beta sheet and we can tell because the beta strands are all pointing in the same direction in terms of their N N C terminal ends. And so this is one continuous poly peptide chain here. So we know that this is an interchange parallel beta sheet and this is the back of the arrow over here. So this will be the end terminal end, and this is the what the arrows are pointing to. So this is the C terminal end. And so this concludes our initial lesson on the differences between anti parallel and parallel beta sheets. And in our next lesson video, we're gonna be able to talk even mawr differences between these two, specifically the hydrogen bonding differences between the two. But before we get there, let's get some practice. So I'll see you guys in that practice video

So now that we understand the fundamental differences between anti parallel and parallel beta sheets, let's talk about the differences between hydrogen bonding of the anti parallel and parallel beta sheets. And so what's important to note is that both anti parallel and parallel beta sheets are stabilized by hydrogen bonds that form between the Carbonnel group and the amino groups on the backbones of adjacent beta strands. And so again, what this means is that the our groups are not involved in stabilizing the beta sheet. And so that's something that's very important. And this is also true for Alfa He'll ISI. So this is something that's true for really secondary structures. Are groups are not involved. It's all about the backbone. And so, really, this is how beta sheet hydrogen bonding works. So each amino acid residue in both anti parallel and parallel beta sheets on lee forms to hydrogen bonds. But the hydrogen bonding is still slightly different, and so here's how it works. With anti parallel beta sheets, they actually have stronger bonds that are actually pretty much perfectly perpendicular, so they have stronger hydrogen bonds that air pretty much perfectly perpendicular, and because they're stronger hydrogen bonds. Those bonds are going to be mawr stable. And because they're more stable hydrogen bonds, anti parallel beta sheets are going to be more prevalent and more common and proteins found in nature than parallel beta sheets. But that's not to say that parallel beta sheets are never found because they are. And so, with parallel beta sheets, they actually have weaker hydrogen bonds, and their hydrogen bonds are actually slightly distorted. So what that means is that they are not perfectly perpendicular. They're not perfectly perpendicular. And again, because parallel beta sheets have weaker, distorted hydrogen bonds that air not perfectly perpendicular, they're going to be less stable. And because they're less stable, they're gonna be less commonly found and proteins found in nature. So it's something that's important to keep in mind. So in our example below, we're going to distinguish between anti parallel parallel beta sheet, hydrogen bonding or H bonding. And so notice on the left. Here, what we have is our anti parallel beta sheets, so these are anti parallel beta sheets, and then on the right. What we have are are parallel beta sheet, and so, which will see, is that the anti parallel beta sheet. Remember, it is slightly mawr extended because it has a rise per residue of 3.5 angstrom, so it's a little bit mawr extended, whereas the parallel beta sheet on lee has a rise per residue of just 3.2 ancient, so it's slightly less extended. So, really, what you'll notice is both residues again, and both anti parallel and parallel beta sheets are going to form to hydrogen bonds, so there's nothing different about the amount of hydrogen bonds still the same amount. But what you'll notice is that there's gonna be some slight differences. So for anti parallel beta sheets, both of the hydrogen bonds on a residue actually link to just one residue on the other strand. And so, if we were to highlight a single residue. So let's highlight this residue, which is box in this dotted line. Here, notice that the two hydrogen bonds of this single residue right here the two hydrogen bonds are right down here in these highlighted in red down below with these dotted lines. So those two hydrogen bonds Onley connect toe one single residue on the opposite strand here, and so really, it's just the hydrogen bonds link from one residue to just one residue on the other strand. And that's the way anti parallel beta sheets work, so it's a little bit easier to think about it a little bit more straightforward now with parallel beta sheets, on the other hand, noticed that we have one residue over here and dotted like this and again, it still has to hydrogen bonds, but both hydrogen bonds of a residue linked toe, two different residues. So they linked to two residues on the other strand and so noticed that we've got to hydrogen bonds one over here and one over here, and they're slightly distorted. They're not perfectly perpendicular like they were over here. They're perfectly perpendicular to the direction off the beta strength. But these are slightly distorted, noticed that they're going off at slight different angles and so also noticed that they're connecting to two different residues on the opposite strands. So it's connecting toe one residue over here with this hydrogen bond, and then the other hydrogen bond, which is over here, is connecting to another residue, which is this one over here, and so that is really the major difference here that the hydrogen bonds connected to residues with parallel beta sheets and with anti parallel beta sheets. There's just both hydrogen bonds of a residue connect toe, one residue on the other strand, which is what allows for the hydrogen bonds to be stronger perpendicular. And that's why anti parallel beta sheets again arm or commonly found and more stable. So that concludes our lesson here on the differences between anti parallel parallel beta sheet hydrogen bonding and in our next couple of videos will be able to get some practice so I'll see you guys in those practice videos.