Aromatic Amino Acids - Video Tutorials & Practice Problems
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Aromatic Amino Acids
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In this video, we're gonna talk about our second group of amino acids, the aromatic amino acids. So the aromatic amino acids all have really big R groups with big benzene rings. And so recall from your previous organic chemistry courses that a benzene ring is just a 6 membered carbon ring with a conjugated double bond system just like the one that's shown right here. And also recall from your previous organic chemistry courses that the benzene ring can be shown with a circle in the middle to represent that conjugated double bond system. Now, it turns out that there's only 3 amino acids that are categorized as aromatic and those are phenylalanine, tyrosine and tryptophan. And so down below, we have a mnemonic to help you guys memorize those 3 aromatic amino acids, and that mnemonic is just f y w or fat young whippersnappers. And so, whippersnappers, believe it or not, is actually a real word. If you Google the definition of whippersnappers, you'll see that it's someone that is young, inexperienced, and overconfident. And, really, these aromatic amino acids, Phenylalanine, Tyrosine, and tryptophan, act like young, overconfident whippersnappers because they feel like they can go into whatever amino acid group they want. And so, not that I expect you guys to know this right now, but Phenylalanine is like, I could be categorized into the non polar group. Tyrosine is like, I could be categorized into the polar group. And tryptophan is like, I could be categorized into the tryptophan is like, I could be categorized into the non polar group or into the polar group. And you'll even see that some textbooks categorize these amino acids in that way. And so they really do act like young whippersnappers that feel like they can go into multiple of these amino acid groups. And so that's why we've categorized them all together as the aromatic amino acids because they have these big benzene rings. And so now that we know that they are indeed young whippersnappers, that they are also fat because they have these big benzene rings. And so hopefully by remembering FYW, or fat young whippersnappers, that'll help you guys remember the aromatic amino acids of Phenylalanine, Tyrosine, and tryptophan. And so, down below, we're gonna talk about the structures of each of these amino acids. And we're gonna start with f here, which is for phenylalanine. And so notice on the far left block over here, what we have is phenylalanine, and phenylalanine's 3 letter amino acid code is phe, and its one letter amino acid code is phonetic with an f. And so literally phenylalanine is trying to tell us what its r group structure is. It's literally telling us that it's alanine, our leader amino acid, with a phenyl group branching off of it. And that's exactly what we have down below. That phenylalanine or f here is literally just our leader amino acid alanine with a phenyl group branching off. And so recall from your previous organic chemistry courses that a phenyl group is literally just a branching benzene ring. And so when we're drawing phenylalanine structure, we can literally just draw alanine, which we know is a CH3, but we know that the number of hydrogens are gonna change, so it's gonna end up being just 2. And then we can draw a branching phenyl group, and so that's just a branching benzene ring. And so that is it. That is phenylalanine structure. It's literally just alanine, our leader amino acid shown here with a phenyl group branching off. So pretty easy. Right? So our next aromatic amino acid is y and y is for tyrosine, which is what we have in our next block over here. And tyrosine's three letter code is t y r, and its one letter code is y phonetically for tyrosine. And so tyrosine structure is literally branching directly off of phenylalanine structure. And so that's exactly what we have down below, that tyrosine is literally just phenylalanine having a hydroxyl group baby or a hydroxyl baby. And so if we go back up to our image up above, the only place that makes sense for a hydroxyl group baby to come out of this benzene ring is from the bottom of the benzene ring. And so it doesn't make sense for our benzene ring, our hydroxyl group to come off of the sides or come off of the top. Our hydroxyl group baby has to come off of the bottom. And so down below, when we draw a Tyrosine structure, because we know that it's literally phenylalanine, We can draw phenylalanine exactly. So phenylalanine is literally like this. So that is phenylalanine. And then it's Phenylalanine having a hydroxyl group baby, which means that the hydroxyl group has to be coming off of the bottom of the, benzene ring here. And so it doesn't come off of the sides or anywhere else. It comes off of the bottom. And so, that can hopefully, help you guys remember Tyrosine's r group, because literally, this is Tyrosine's r group. And so over here on the right, what we have is an image of a baby's head coming out upside down, and this circular head can help remind you guys of the circular oxygen atom in the hydroxyl group. And so another way to remember Tyrosine structure is to recognize that Tyrosine kind of sounds like a tire, and tires are circular just like this benzene ring is up here. And so, the tyrosine can help remind you guys of the Oh group that is branching off of the tire. And so hopefully, that's another way that you can use to remember tyrosine's structure. So then last but not least, what we have is our last aromatic amino acid of the w, and the w is for tryptophan, which is what we have in our last block over here. And so tryptophan's three letter code is t r p, and its one letter code is phonetic with a w, because the way that Bugs Bunny would say it is, twitophan with a w in it. And so down below, what you'll see is that tryptophan structure, the w here, is literally just our leader amino acid again, alanine with 2 joined rings. The first join ring is a 5 membered ring, and the second join ring is a 6 membered carbon ring, which is a benzene ring. Now it's important to note that the benzene ring is going to go below. The benzene is below the structure. And because the benzene is below, we're going to draw that benzene ring last. So first, we're gonna draw our 5 5 membered ring. And so if we start to draw a tryptophan structure, we know that it's literally just our leader amino acid alanine with 2 joined rings. And so if we draw alanine, we know it's CH 3, but we know that the number of hydrogens are going to change here, it's going to end up being 2. And then it has 2 joined rings, a 5 membered ring and a 6 membered ring. But that 6 membered benzene ring goes below, so we draw it last, which means that we draw the 5 membered ring first. So here is our 5 membered ring. Perfect. So, next what we need to do is realize that our, R group and tryptophan structure has a nitrogen atom in it. And so, to figure out where this nitrogen atom actually goes, we can remember that tryptophan trips on a tripod, and we know that tripods have 3 legs, so that can remind us that there's a 3 carbon start to this nitrogen atom. And so looking up above at our r group, so notice the r group starts to begin right here, so our 3 carbon start would be 1 carbon right here, 2 carbon right here, and then we've got 2 different pathways that we could take. We could take this pathway over here, which is our 3rd carbon, and then that would mean that our nitrogen goes right here. So we would have a 123 carbon start and then our nitrogen atom. So that's one possibility. The other possibility would have 1, 2 carbons and then have our 3rd carbon be over here, and that would mean that our nitrogen would go right here. And so either possibility is possible, and it doesn't really matter which one you pick. Now, I'm gonna pick this second possibility here just because of space reasons. So let's get rid of these dots and let's put our nitrogen over here. So now that we know where our nitrogen atom is, the next thing that we need to realize is that, there what there's a 3 carbon start to our nitrogen, and so we just, identified that. And so the next part that we need to realize is that this nitrogen atom right here is not so the nitrogen atom is not part of the benzene ring. And so we know that the benzene ring is going to be below our structure, and so we know that these rings are joined. So that means that the benzene ring has to share a side with this other ring that's here. But if the benzene ring shares a side on this side or on this side of the 5 member ring, then the benzene ring is going to be up above the structure. But we know that the benzene ring has to be below the structure, which means that the benzene ring has to share a side on either this side, this side or this side. But we know that the nitrogen atom cannot be part of the benzene, which means that the benzene cannot go on this side or on this side because, otherwise, the nitrogen atom would be part of the benzene. So that means that the only place that the benzene can go is on this side right here. So then we can draw in our benzene structure here, and that is our benzene. And so you can see now that it is below the structure. It has the lowest point on our structure here. And so, the last, the very last part here is going to be to draw in the double bond, and the double bond does not touch, so the double bond does not touch the nitrogen or the benzene ring, and so the double bond goes right at this position here. And then, of course, we can draw in our hydrogens coming off of the nitrogen atom, and that is it for tryptophan structure. So, that, essentially concludes our lesson on the aromatic amino acids, and, we'll be able to get some practice utilizing all of these memory tools and our next practice problem. So I'll see you guys there.
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Problem
Problem
Draw in the R-groups from memory for each of the aromatic amino acids.