Draw in the R-groups from memory for each of the charged amino...

Question

Draw in the R-groups from memory for each of the charged amino acids at physiological pH.

Structures of charged amino acids D, E, K, R, and H with R-groups at physiological pH.

Accepted Answer

So this practice problem wants us to draw in the r groups from memory for each of the charged amino acids at physiological pH. And remember that at physiological pH, the r groups of these charged amino acids are gonna tend to have a charge on them. So we're we're gonna wanna draw them in their charged state. And so recall that the mnemonic that we have for memorizing these charged amino acids is dragons eat knights riding horses. And so the d and the e here stand for aspartic acid and glutamic acid, which are gonna have a negative charge on them. And then the knights riding horses is gonna stand for lysine, arginine, and histidine, which have a positive charge in their r groups. And so the first one that we have here is d, and d again stands for aspartic acid or just aspartate. And remember, aspartate. And remember, aspartic acid and aspartate are basically the same amino acid, they just differ by a single hydrogen atom, and so that makes them a conjugate acid conjugate base pair. And so because we're drawing the charged amino acids at physiological pH, we're gonna wanna draw the one with a charge on it. So we're gonna wanna draw aspartate. And so remember that aspartate or aspartic acid here, it's just gonna it's just gonna be alanine with a carboxylate group coming off of it. So it's gonna be alanine, so we know it's gonna have a carbon with a hydrogen, and we know the hydrogens are gonna change, so it's gonna be 2 actually. And then it's gonna be a carboxylate group coming off, so it's gonna be c double bond o with our o minus charge on there. And so that's it. That's the structure of, as aspartate. So we've got our carboxylate group here, and it's alanine with a carboxylate group. Now, the next one is E, and remember E stands for glutamic acid or just glutamate because we want it in the charged state. And so, glutamate has the GLUT in it and so, we know that one way that we can think about this is by remembering that it feeds off of the previous structure in our system. So the E feeds off of the D here like that. And so, we know that because it has the glute, it's gonna have the extra butt area, right? The extra glute area, and the extra glute area is represented by an extra CH 2. And so all we need to do is draw the same exact structure, except with an additional CH 2. So we go and draw that in, so we know we're gonna have our 1st CH2, we know we're gonna have our 2nd CH2, and then we're gonna have our carboxylate group, so it's going to be our C double bond o with an o minus. And so again, we've got our carboxylate group at the bottom and the only thing that's really changed from the previous is that we've just got an additional c h two that's been added in. And that's it. That's the structure of glutamic acid or, glutamate. Now, for the next one that we have is k, and k is lysine. And remember, k here stands for the knight and, really lysine's R group looks like a knight's sword. And just like the k has 4 pointy ends on it that you could try to poke somebody with, there's gonna be a 4 carbon start to this chain. So we can draw in our 4 carbon start, so it'll be ch 2, ch 2, there's ch 2, that's 3, and ch 2, that's 4. Perfect. Now we've got our 4 carbon chart, start to the chain. We know that there's gonna be an amino group at the very end, and so we can go ahead and draw in our amino group. Since we know that all of these positively charged basic amino acids here have amino groups in them, and so it's gonna have a positive charge. And that's it, that's the structure of lysine. Now, the next one that we have is arginine. And remember, arginine has features of both the knight and the horse. So let's skip arginine for now and let's go to histidine, just like we did in our concept. And so with histidine, remember its three letter code is h I s, so one letter code is h, and it stands for the horse. And so really all histidine is is alanine with a 5 membered ring. So we can draw an alanine CH 2 and it's gonna have a 5 membered ring, 1, 2, 3, 4, 5. And then just like the h has 2 parallel lines, there's going to be 2 double bonds and 2 nitrogens. And so it also looks like a sideways horse. We know that it's gonna look like a sideways horse. So we can draw in our back legs, our front legs, we know that there's gonna be a neck here, and then we know that the neck is gonna be positively charged. So it's gonna have an h and this is going to be positively charged. And then if we wanted to, we could even draw in a little back tail for our horse if we wanted to. And then, the last part is to realize where does that second nitrogen go? Now that we have 2 double bonds and 1 nitrogen, where does the second nitrogen go? And you have to remember that the horse here is not stepping on the second nitrogen. And so that means that the only place that the second nitrogen can go is right here. So all we need to do is add in its hydrogen and that's it. That's the structure of histidine. And then lastly, what we have is arginine, which again has features of both the sword and the horse. And so what we're gonna do because it has features of the sword is we're going to, count how many pointy ends you could try to poke somebody with r. And so, really, you could try with these three points here. And so what that means is that there goes there's gonna be a 3 carbon start to our chain. So it will be CH 2, CH 2, and CH 2. Perfect. So there's our 3 carbon start, and also just like there's 3 pointy ends on our r, there's gonna be a triangular nitrogen structure at the bottom that's somewhat gonna resemble a person riding a horse. And so, the way that that works is we get our nitrogen, our carbon, and our nitrogen, and then our double bond O. And so, again, here is our Oops. I'm sorry. Not a double bond O, a double bond nitrogen. And so, you can see that we've got our triangular nitrogen structure in here. And so now, all we need to do is fill in the hydrogens. And we know that this one's only gonna have 1, this one will have 2, and the one that's up top is going to be the one that is positively charged. So this is the structure of arginine. And so, hopefully, utilizing those, memory tools help you guys remember the structures and I'll see you guys in our next practice problem.

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Draw in the R-groups from memory for each of the charged amino acids at physiological pH.

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