The endorphins are a group of naturally occurring neurotransmitters that act in a manner similar to morphine to control pain. Research has shown that the biologically active parts of the endorphin molecules are simple pentapeptides called enkephalins. Draw the structure of the methionine enkephalin with the sequence Tyr-Gly-Gly-Phe-Met. Identify the N-terminal and C-terminal amino acids.

Question

Accepted Answer

Welcome back everyone. Our next problem says thyrotropin releasing hormone trh is generated by neurons located in the hypothalamus and it acts as an inducer for the anterior pituitary to secrete prolactin and thyroid stimulating hormone TSH. The substance is composed of and here we have an amino acid sequence written in the form of three letter abbreviations. So we have GLN hyphen his hyphen pr O hyphen gly. This sequence followed by either lys hyphen arg or arg hyphen arg sequences. What is the structure of the sequence? Gln hyphen? His hyphen pr O hyphen gly hyphen lys hyphen A RG. What are its N terminal and C terminal amino acids? Well, we can clear out one question right away by convention, amino acids are always written with the N terminal. So that NH two group on the left and the C terminal, that carboxylic acid group on the right. So when we write an amino acid sequence in conventional writing order left to right, the first amino acid in that sequence will be the N terminal since thats on the left and the last amino acid in that sequence will be the C terminal since that's on the right. So GLN or glutamine will be our n terminal amino acid highlight that in yellow and A RG or arginine will be our c terminal amino acid. Let's clear that one out of Wei Wei and focus on the big one. This problem says what is the structure of the sequence? We've got six amino acids, a polypeptide. This is gonna be a big old structure. So we need to think through this carefully. So we start by thinking about what is the basic structure of all amino acids. How do they join together to make a polypeptide chain like we have here? And then what are the specific R groups for each of these amino acids? So we can draw this particular sequence. So of course, our backbone structure of every amino acid and I'm going to write it in the neutral form rather than in the sw sweater ion form. So I could also exist as a charged molecule with two opposing a positive and negative charge. But I'm writing it in neutral form just to make it a little less cluttered. So we have NH two, it's our, it's our n terminal followed by a carbon which has a hydrogen on it. And this carbon is bonded to the R group that distinguishes each amino acid from the other. This is the alpha carbon and it is bonded also to a carbonel group. This is part of a carboxylic acid. So that carbonyl carbon also has an oh group on it. So that's our individual amino acid. And of course, it can react with another amino acid. So I'll write that same background NH two, the alpha carbon with its hydrogen, I'll write R prime to show it can be a different amino acid followed by the carboxylic acid group. So these two can react together losing the hydroxy group from the carboxylic acid of our first amino acid and a hydrogen from the NH two group. On the second, they can react to losing a water molecule to form a peptide bond between the carbon carbon, which is now directly bonded to the nitrogen on the n terminal end of the second amino acid. So that's how our amino acids will be joined together with those peptide bonds. I've highlighted it in blue and I'll continue doing that in my structure. So we can keep track of when we're transitioning to a new amino acid. So we have our basic overall notion of how the backbones bond together. Now, we just need to think about what the R groups are for each of the amino acids in our polypeptide sequence to be able to draw the specific structure. So I'm just going to draw a line across here separating this from the next step. So we'll now work through each amino acid at a time thinking about its R group. So starting with GLN which is glutamine. So this our group of glutamine is ch two CH two, then ac double bonded to an O with an NH two. So it's an amid on the end there. So I've drawn this in red and when I draw my structure, I'm going to draw my backbone in blue and my R groups in red. And again, just to help us keep track, this is a long molecule and I want to keep track of where I am, keep oriented here. So let's start with the backbone of our first amino acid, this glum mean. So I'll start with that N terminal. So again in blue, I am drawing H two N and that's bonded too, the alpha carbon which is then attached to the carbon carbon. So adding this double bond to an oxygen and then that will be where the peptide bond will be to the nitrogen of the next amino acid. So I've now transitioned to amino acid, the backbone of amino acid number two. Remember I haven't added my art group yet. So to keep track of this, I'm going to highlight that peptide blonde in blue. So I know where I'm moving on to the next one. So now I just need to add the R group for my glutamine note, I'm drawing a skeletal structure here. I wrote my other structures in terms of my peptide bond formation of my R groups in a condensed structural formula, but that will get way too bulky when drawing the whole polypeptide chain. So I'm now working on a skeletal structure. So for glutamine, I have two ch two groups. So again, extending from the alpha carbon in the backbone, I have the CH two CH two and then there's a carbon carbon. So there's a bond to that carbon carbon with a double bond to an oxygen. And then it has the NH two group at the end. Now note it was looking at glutamine here that made me decide to do these in two different colors because the structure of the glutamine R group is extremely similar to the backbone structure of the amino acid itself. So if I started drawing this R group on here, it would be really confusing to look back over and see where's the N terminal of the backbone versus that NH two group on my glutamine R group. So just keeping them distinguished there can help us keep track as we go along. So here is the glutamine, that's my first amino acid in the chain. Well, I've gotten started on my backbone of number two because I already have this nitrogen drawn here. So we're going to move on to our Histidine his, which is the next amino acid. And I'll put little boxes around my abbreviations just to try and keep things separate here. Histidine has a little complicated R group. It has what's called an Ada zole ring. So it has CH two and then a bond to this five atom ring which going from the carbon, which I'll call carbon number one, which is attached to the CH two. I have that carbon single bonded to a nitrogen which has a single bond to another carbon, which has a double bond to a nitrogen, single bond to a carbon and then double bond back to carbon one. So again, that's an a midas all group. So a little tricky to draw here. So now again, I have my nitrogen there. That's the backbone of my histamine. So that nitrogen needs to be bonded to a, the alpha carbon group. And then that alpha carbon has that bond to the carbon carbon, put in my double bond to an O. And now I'll get to my next peptide bond there. Highlight that in blue, just keeping that straight and let's add on my Amita zole R group. So I'm now going to scroll up a bit. I don't need most of the text of this problem. Just the list of my peptides and I'm going to run out of space. So let me put on that and metasol ring. So I've added on that R group for my histine residue. So I'll just write his over there to show where that is. Again. Now let's move on to my next amino acid pr O which is proline. I have that first nitrogen for it. And now I have to think about the R group on prolene. So let's draw or the backbone structure first, excuse me, and you get mixed up here and something like this. So I have that first nitrogen and the peptide bond. And then I draw the link to the alpha carbon and then the bond to the carbon carbon put on that double bond to the O and then the bond to the next nitrogen, which is our peptide bond highlight in blue. And now we need to draw the R group. But when it comes to prolene, that's a little tricky. Prolene is a very interesting one in that the R group of prolene brink comes back around like in a ring and bonds to the nitrogen in the backbone as well as the alpha carbon. So you'll notice in the my drawing of the structure of its R group, I have some in blue and some in red. So the blue atoms are part of the amino acid backbone. So I have a nitrogen then a carbon that carbon is the alpha carbon. You can see it bonded there to the carbon carbon and the bond that would usually be the R group going from the alpha carbon then has ach two ch two ch two. So three carbons, that third carbon is then bonded to the nitrogen from the backbone structure. So it makes a little ring as in our group. So that's very interesting. So a little bit tricky to draw on a structure like this, but we'll add it in. And again, here's where I like having the R group in red to keep track and keep myself oriented here. So I've put my three carbon ring in here attached back to the nitrogen. Notice that means I won't add a hydrogen onto this nitrogen in general, that nitrogen in the backbone has one hydrogen attached. But because of the ring here, the nitrogen does not have a hydrogen. So we're done with Prolene ready to move on to our next residue, which is gly or glycine. And glycine is kind of a nice break here because glycine, the it's our group is just a hydrogen atom. So nice and simple, we don't even have to draw it on here because in a skeletal structure, we don't indicate hydrogens that are attached to carbons, they are implied. So let's add the backbone here. So we've already got the nitrogen, give it its hydrogen, it's bond two and alpha carbon, then the carbon carbon. So add the C with the double bond to an O and then the peptide bond to the next amino acid highlight in blue to keep track. And again, in this case, I don't need to add anything to my structure. There's my alpha carbon, it now has two hydrogens instead of just one, but that's implied by the skeletal structure. So we'll write gly here to note that thats our Glycine amino acid. So we're working our way through just two amino acids left. Our next amino acid is lysine. So let's look at that. Our group I seen as a bit of a long chain here. It has four carbons, ch two, ch, two, ch, two, CH two and then NH two. So, well, let's finish the backbone. We've got the nitrogen already attached, accidentally drew that bond in red, attached to our alpha carbon, which is attached to a carbon carbon. So add the C double bond O which has the peptide bond to the next nitrogen, put the hydrogen on our backbone nitrogen and highlight the peptide bond. And now just at our R group in red, it's going to be a little squished here since it's a long chain left to draw sort of short bonds. So we have four carbons. So we make that zigzag shape for a skeletal structure. So one, 234 carbons, 1234. And then last of all that bond two, an NH two group at the very end, squeeze that right in there. So this is our lysine amino acid. And finally, we're on our c terminal amino acid A RG or arginine. So let's look at that our group. It's another long chain with three carbons, ch two ch two CH two, then NH then another carbon that carbon has a double bond to an N which has an H and then a single bond to an NH two group. So another kind of long chain R group. So I already have the nitrogen in here give it its hydrogen that gets attached to the carbon carbon, which is bonded to excuse me, that gets attached to the alpha carbon which gets bonded to the carbon carbon. So add that C double on to an O, we are now at the C terminal. So that carbon carbon has a bond to an oh to end the polypeptide chain. So the last thing I need to do is add my arginine R group. So I have three carbons. So bonded to the alpha carbon 123, the third carbon has a bond to a nitrogen which has one hydrogen on it. That nitrogen is a bond to another carbon. And that final carbon has a double bond to an NH and a single bond to an NH two group. So it ends up in sort of that branch there. So now I'm just going to draw a line to kind of barricade off my our group diagrams here and kind of isolate my structure. I finished off with my last arginine amino acid and now I have my whole giant peptide structure here. The N terminal starting with glutamine with each one. We see our peptide bond between each amino acid connecting that carbon carbon with the nitrogen and our our groups for all of our amino acids finishing up at the c terminal arginine. See you in the next video.

Verified video answer for a similar problem:

Key Concepts

Endorphins and Enkephalins

Amino Acid Structure

N-terminal and C-terminal