For each figure, highlight each bond with limited rotation &am...

Question

For each figure, highlight each bond with limited rotation & determine the conformation of each peptide group.

A. Diagram of a peptide group showing bonds with limited rotation and R groups.

B. Chemical structure of a peptide bond with nitrogen and carbon atoms.

C. Chemical structure of a peptide bond with nitrogen and carbon atoms.

Accepted Answer

So this practice problem says, for each of the figures below, highlight each bond with limited rotation and determine the confirmation of each of the r 2, and r 3. And so because we have 3 different R groups with r one, r 2, and r 3. And so because we have 3 different r groups, that means that we have 3 different residues in this peptide. And when we have 3 residues, that tells us that we have 2 peptide bonds. And we know we only have 2 peptide bonds because remember, the number of peptide bonds is always gonna be 1 minus the number of residues. And so if we have 3 residues and subtract 1, that tells us there's 2 peptide bonds. And we know that peptide bonds have limited rotation, so let's go and find these peptide bonds. And recall, a quick way to be able to find the peptide bonds is to look for the carbonyl groups because they kinda stand out. And so the carbonyl groups are c double bond o, and so here we have a carbonyl group. And we know that peptide bonds are amide linkages, and so that means that the carbonyl group has to link to a nitrogen atom. So here's our nitrogen atom. And so, what you can see is that this link between them right here must be a peptide bond, and indeed it is. And so here's our 1st peptide bond. So now, we check our next carbonyl group and here it is over here and the carbonyl group again has to be linked to another nitrogen. And so that means that this bond right here has to be a peptide bond. So now, let's check our last carbonyl group which is right here, and notice that it is not linked to a nitrogen, so that means that this is not a peptide bond. And so these are our 2 peptide bonds right here. And so now that we found our peptide bonds, we know that they're going to have limited rotation and let's determine the conformation of the peptide group. So remember that the way we determine the conformation is we imagine an imaginary line going through it and then we look at the 2 bulky groups. And so we've got a bulky group on this side going this way and on this side, our bulky group is going this way. So this whole thing would be the bulky group. And so notice that these bulky groups are on opposite sides of the double bond going away from each other. And this is a, a type of trans conformation. So this is a trans conformation. So what we can do is we can label this conformation as trans. So now let's check this double bond over here and we can do the same thing. We can put an imaginary line through this and look at its bulky groups. So notice that it has one bulky group going this way and then it has another bulky group, which is this one going this way. And so this bulky group these 2 bulky groups again are on opposite sides of the double bond, which means that they are also in the trans conformation. So we can label this double bond this peptide bond as well as being in the trans conformation. So both of these are in the trans. And then also recall that, any bond that has a double bond is gonna be have limited rotation. So really, the, carbonyl group double bonds are also gonna have limited rotation. And so, all of the other bonds that are not highlighted here are gonna be able to have more rotation. They're not limited in their rotation, and so they have free rotation. So now, let's check b over here. And what we have with b, what you'll notice is that we have, a proline amino acid residue. So you can see here that we've got this, n c c, so it goes n c c. And, we know that the middle c here is going to be an alpha carbon. And notice that this alpha carbon, the R group, goes out, goes out, back, and connects back to the nitrogen. So this is a proline residue here. And so with this proline residue, we can see that, the way that we identify the the peptide bond is to look for the carbonyl group. So here's a carbonyl group and we know that the carbonyl group is gonna be bonded to a nitrogen, so that means that this bond in between these two must be a peptide bond, and indeed it is. And so, what we can see here is that this peptide bond right here, when we draw the imaginary line through it like this, and we know that the r here represents the rest of the molecule, so this r here is a big bulky group. Opposite this is the big bulky group. And so these 2 big bulky groups are on opposite sides of the peptide bond. So this means that this peptide bond is gonna be in a transconformation. So what we can do is say that this peptide bond here is in a transconformation. So now, if we check this one over here, notice that, again, we have another proline residue, and this is the alpha carbon here. And this time, again, what we see is, here's our carbonyl group and here's our nitrogen. So this time, what we see is this is the peptide bond. And with this peptide bond, what we'll see is that if we draw our imaginary line through it like this, what you'll see is that our big bulky groups, so this r group here, which is the rest of the molecule, and this part over here, this group over here is also the other bulky group. They are on both on the same side of the peptide bond, which means that this is in the cis conformation. And so recall that proline residues are the ones that can be in the cis conformation. So they do not have a preference for the trans or the cis conformation. And this is the exception that can take on either conformation. So, what we've done here is we've highlighted all of the bonds that have limited rotation except for these bonds right here, which we know all double bonds are gonna have limited rotation. And so now, we've completed this practice problem. We've highlighted all the bonds with limited rotation and we've determined the confirmation for each of the peptide groups that are shown. So that concludes this practice problem and I'll see you guys in our next video.

Struggling with Biochemistry?

For each figure, highlight each bond with limited rotation & determine the conformation of each peptide group.
A.
B.
C.

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Peptide Group practice set

Struggling with Biochemistry?

For each figure, highlight each bond with limited rotation & determine the conformation of each peptide group.A.B.C.

Watch next

Peptide Group practice set

For each figure, highlight each bond with limited rotation & determine the conformation of each peptide group.
A.
B.
C.