Identify the amino acids in the following dipeptide and tripeptide, and write the abbreviated forms of the peptide names. Copy the dipeptides, draw a box around the peptide bonds, and use an arrow to identify the α-carbon atoms. Draw a circle around the R groups, and indicate if the R groups are neutral, polar, acidic, or basic.
a.

Question

Identify the amino acids in the following dipeptide and tripeptide, and write the abbreviated forms of the peptide names. Copy the dipeptides, draw a box around the peptide bonds, and use an arrow to identify the α-carbon atoms. Draw a circle around the R groups, and indicate if the R groups are neutral, polar, acidic, or basic.
a.

a. Diagram of a dipeptide and tripeptide showing peptide bonds, α-carbons, and R groups with annotations for their properties.

Accepted Answer

Welcome back. Everyone. Here's our next problem. Consider the following peptide and we have a condensed structural formula showing a peptide here fairly long, definitely more than one amino acid. And then we'll go back and look at this in more detail in a moment. Our problem says, identify the amino acids present, write the abbreviated forms of the names. And then it says box, the peptide bonds, I draw a little box around the word peptide bonds to remind me, mark the alpha carbon atoms with an asterisk and encircle. The our groups little circle around our group there classify the R groups as basic acidic, polar or neutral. So we have a lot to do here. So let's start by looking at where are the backbones of these amino acids? How many do we have? Where are our groups? So finding the peptide bonds and the R groups are sort of the top priority here. So let's recall what the basic form of an amino acid is. So we have, we draw by convention with the amino group first, the N terminal on the left side. So we have H two N and that's bonded to an alpha carbon. So I'll put a little asterisk since that's how we're going to notate it on our structure, which has a hydrogen and an R group that alpha carbon has a bond to a carbon carbon. This is a carboxylic acid group. So that carbon also has a bond to an oh and we can of course, combine two of these amino acids lose a water molecule and make a peptide bond between them. So we lose the oh from our carboxylic acid on the first amino acid, put another little asterisk on my other alpha carbon and then I lose a hydrogen from the NH two group on my second amino acid. And that connects the two with a peptide bond creating this bond that I'll highlight in red between the carbon carbon of the first amino acid and the nitrogen of the second. So with that in mind, let's hunt for our backbones and look for the peptide bonds which we're going to box one, box them in red just to make them stand out a little bit. So looking at our structure. Well, first of all, we don't see an NH two on the left, we see H three C connected to ach with another CH three. So sort of an isopropyl branch connected to a carbon and that carbon is connected to the NH two going down. So there's our first NH two, that's the beginning of the backbone. So we have NH two and then ac with an H that's our alpha carbon. So the alpha carbon, I'm going to put an asterisk on looks like the third carbon in the chain the way our polypeptide chain is drawn. So I have the alpha carbon labeled. So now I can tell that the isopropyl group here is actually the R group of our first amino acid. So I'm going to circle, that is a purple group and I'll say that's the R group. So a red circle since we're supposed to encircle the R groups, and then I can look for my peptide bond, which I need to box. So I have that alpha carbon which I've put an asterisk on. It's bonded to that carbonel group C double bond to O which now has a bond to and NH so there's the peptide bond. So we'll put a box around it. Then the NH is the beginning of a new amino acid. So I have the nitrogen connected to ach that is the alpha carbon. So put an asterisk there from that ch we have a branch coming off that has a carbonyl carbon attached to an oh, so we have this carboxylic acid group, put a ring around that because that's the R group of our second amino acid or so I thought because when I keep going to find out to keep going along the backbone and see if I have more amino acids, if this is the alpha carbon that I just labeled here. And that's the R group that I just circled. My next atom should be a carbon group because we have nitrogen, alpha carbon. Next should be a carbon carbon. Instead I have ACH two and then another CH two, I have a four carbon chain with an NH two at the end. So I've mislabeled the R group. So this was drawn in sort of a tricky fashion. So I'm going to erase that last ring I drew. This is not the R group, but instead the remainder of the backbone, that's the C terminal of my second amino acid. The R group instead is continuing along what looks like the main chain. So the R group is going to be CH two ch two, ch two, CH two and H two. So I'm going to put a ring around that part of my structure. And that carboxylic acid group again is the backbone there. So I have two amino acids, therefore, one peptide bond that I've put a box around two alpha carbons that I've put asterisk on and my two R groups. So I've notated my structure as I'm supposed to. Now, I need to identify the amino acids which of course will be done by their R groups. So my first R group is this isopropyl chain. This is the amino acid vine which its abbreviated form is VA L. Of course, we have capital va V lowercase A lowercase L as the format of the amino acid name and I'm going to rewrite that in blue. So I can highlight it in yellow. I like to use the yellow to remind myself of the answers I'm looking for. So I've got Valine for my first amino acid va L then the second amino acid, this four, this chain of four carbons and then an NH two group is the amino acid lysine and it's abbreviated LYS. So there's our abbreviation for the second amino acid. So what else is left? I've identified mine amino acids and written their abbreviated form boxed, the peptide bonds marked the alpha carbons circled the R groups. Last I just need to classify those R groups as basic acidic, polar or neutral. So basic versus acidic. My basic are groups are going to have, I mean, or I mean derivatives in there are groups because then they can accept protons. Now, of course, there are other ways for compounds or side chains to be basic. But we know that in amino acids that we find in nature in humans, there are basically just 20 of them. And the ones that we find most commonly, this is how they are basic. Then an acidic for an Ame in our group to be acidic. The acidic R groups have carboxylic acid groups and of course, those can donate protons, therefore acting as an acid and then polar versus neutral. Well, that's pretty simple. We've got polar, our groups which are charged, some have charged or have electro negative atoms bonded to hydrogen atoms so capable of hydrogen bonding and then our neutral R groups or alkyl groups or have aromatic rings. So with that in mind, let's classify our two amino acid R groups here. So veiling we just have isopropyl, it's a completely a hydrocarbon, no other atoms in there. So this will be a neutral, our group and it won't be acidic or basic. So we'll highlight neutral when we look at LYCEE, we've got those four carbons with hydrogen. So four ch two groups, but it ends in an NH two group and therefore ends in aming group and therefore is basic. And as we'd expect of a basic amino acid, since it has that NH two group, it's also polar since nitrogen is much more electron than hydrogen. So we have that capability for hydrogen bonding and therefore a polar R group. So again, the final part of this answer is that we have veiling being a neutral R group and lyne having a polar and basic R group. See you in the next video.

Verified video answer for a similar problem:

Key Concepts

Amino Acids

Peptide Bonds

R Groups and Their Properties