L and D Amino Acids - Video Tutorials & Practice Problems

Representations of L-Configuration

In this video, we're going to be discussing the Chire ality, or what's also known as the configuration off the standard amino acids. So let's get started. So as previously discussed, all of the standard amino acids that are derived from proteins have the same exact type of Cairo ality center, and that is what's in biology or biochemistry, known as an L configuration. But in organic chemistry, we know this better as an s configuration. So just you know, l and s don't always mean the same thing, but specifically in proteins they do. So what that means is, if you specifically have an amino acid that is in an S configuration or counterclockwise configuration, when you calculated out in organic chemistry, that will be an L. But that may not apply if you try to apply it to a different type of molecule, like a sugar that would be a completely different type of configuration. Now, this doesn't apply that there's another type of configuration because remember, for every s, there's also in our and the name that we give in in biochemistry for the our configuration of an amino acid is a D amino acids. So let's just write that down A D amino acid, also known as an R configuration, is possible. Okay, It's the an anti mur of the original s. However, these air not isolated from proteins, so you don't have to worry about these too much. You may see them come up in a practice problem or something theoretical, but for all practical purposes, we're gonna always be sticking to this configuration the S or also known as the L configuration. Awesome. So the point of this video is not to a bunch of RNs naming because that takes up a lot of time. What I love for to accomplish in this video is to give you some shortcuts so that instead of having to calculate rmds every time, you could just look at the molecule and just by looking at it, you'll know whether it's in our or it's an s. Okay, so what I've done here is I've I'm representing four different ways that you might see the common l configuration of the standard amino acids. Okay, so the first one is if you see the amino acid with the with the amine sticking down. Okay, so basically, the amine is sticking down. You can see that the N H two is coming down off of the amino acid. If you see it in that configuration, which we're gonna be using that type of I should say that type of, um, format of drawing it. We're gonna use that kind of rotation often where we have the side chain facing up and the mean facing down. If the immune is facing down, you wanna put it on a wedge? If it's on a wedge, that means that it's going to be. That means that this Carol center will be an s Kyrill center. Okay. No, I'm not gonna prove it to you, But if you want, you can pause the video and calculate it out, and you will see that that indeed is an s. And remember, that s equals l. So this would be an L. Now, what about if the side chain is facing down? So instead of the amine facing down, what about if the side chain is facing down? Well, this is actually the way that I had represented on the previous page in the video. Before this, we were looking at a lot of amino acids that had the Imean facing up and they are facing down. Well, if the R is facing down, then the way that you wanna represent it is on the dash. That will also mean that this Carol center is in the s configuration. Okay, Well, what about if you rotated? What if you rotate it so that the our group is instead facing up? Well, if the our group is facing up, then you're gonna wanna put it on the wedge in orderto indicate the s Kyrill center. Okay. And finally, what about if you have it on a Fisher projection, we're gonna be have We're gonna have to use, um, Fisher projections here. Remember that you can any type of practice with Fisher projections. You can look them up on the clutch prep search bar, and you can do more practice. But this is just a quick tip. If you wanted to draw Fisher projection and you wanted to make it, make sure that it's l or s configuration. You put the mean on the left and an easy way to remember that is the l is left now. L actually does not stand for left, but it just works out nicely that when you want to draw a Fisher projection of an amino acid and you wanna make sure it's in the l configuration, just put the means of the left and then you're all taken care of. That's all you need to do. Well, I mean, facing left and then obviously followed the other rules of Fisher projections, which is that the most oxidized Adam or the carb oxalic acid goes at the top and then the side chain would face straight down as long as you do that and have your means to the left. Your golden. Okay, so I know this might seem like a lot of lots of memories you might be thinking, Johnny, isn't it easier just to do RNs every time? No, it's not because we're gonna be working so much with these amino acids. You want to be able to recognize it, right? By looking at it, you don't wanna have to calculate RNs every time. So in these next practice problems, I hope that I'll make it clear to you why it's easier just to try to memorize these than it is to do r and s every time. Okay, so let's go ahead and move on to an example

Converting Bondline to Fischer Projection

convert the amino acid Hisa Dean into a fissure projection and then indicate if that Carol Center is either are or s. So, guys, you're not at the point where you need to memorize what history and looks like. Yet there it is. It's given to us. But what I want to do is draw the Fisher projection without calculating the arness of the original molecule rolling on a calculated after to make sure that we did it right. So I guess first step, let's draw the backbone of official projection, which is gonna look something like this. Okay, And now we need to determine Are we going to draw an L or a D amino acid? So I look at this amino acid, and how can I easily tell if it's allergy? Well, what I see is that the amine is facing down and the mean happens to be on a wedge. And if the mean is facing down on a wedge, that means this is an S, which is an L. So that means that I didn't even have to calculate it toe planet out. I already know that this is an L, which means that I can put my mean without even thinking about it over here on my left side. Now I need to make sure that everything else is in the appropriate places. Well, so for example, according to the rules of Fisher projections, your most oxidized Adam needs to be the tops. That would be the one of the most oxygen's carb oxalic acid at the top. H has to be on the side because that's the other. That's the other Adam that's attached. That is not the rest of the our group. The rest of the our group has to face straight down. So now all I need to do is draw out. The rest of this are groups that would be ch two. And I'm gonna put another bond here, and I'm just gonna draw the rest of that crazy ring. So let's go ahead and do that here. Um, I'm just gonna flip it around so that I can Oops, There needs to be another nitrogen here. Cool. And then I just need to add my double bonds. And my age is so one double bond would be here and another door one would be here, and then this would have an H and now we're done. We just drew the Fisher projection, but notice that I didn't have to calculate Arness at the beginning. I just did it just by looking at it now to confirm that we did it right. Let's indicate if this Carol Center here is R. R s. Okay, so remember the rules for calculating the R and s of a Fisher projection. If you don't remember, you can type this into the search bar clutch. You can dio or an s configuration of Fisher projections, and it will pop up. And it's a whole video on how to just do that. But I'm just gonna go ahead and assume that you have either already watched that or you remember. So the way we would do it is we would, as always, prioritize our groups. This would be number. Well, no, no. Whoa, that's wrong. Nitrogen is number one. Because nitrogen is the heaviest atom that's a directly attached to the Cairo Center. This one is next cause it's directly attached to two oxygen's carbon attached to oxygen's. This side chain is third because its carbon attached to hydrogen, which isn't as good. And then finally hydrogen is always in last place because it's the smallest, Adam. Great. So remember, the rule says that specifically for Fisher projections. If your last place group is facing down, it looks exactly the way it is. But if you're last place group is facing towards the side, you have to swap. You have to swap whatever letter you get. So that means that I'm gonna go ahead and trace. I'm going to trace from 1 to 2 from 2 to 3. I always skipped four and from three toe one. So this looks like an R configuration now, is it actually are? No, Because notice that my fourth group is horizontal. So that means that I have to swap whatever letter I got. I need to swap it to the other letter. So it's actually gonna be s. And that confirms that I did it correctly. We did draw the S configuration or the l amino acid. Great job. So let's go ahead and try to do a practice problem.