Now, here, we're going to say that peptides are formed when two or more amino acids bond with each other through a peptide bond. Now, here we're going to say the peptide bond also known as an am my bond is when we have the carboxyl group of one amino acid, covalent bonds with the amino group of another amino acid. Now pay attention here, we have the carboxyl group here in its anionic form. So it's negatively charged form and we have the nino group in its positive charge form. Now, if we come down here and we're talking about the formation of a peptide bond, we've kind of seen this before when we talked about the formation of an amide bond, remember that happens through a condensation reaction. We have the loss of water. So here we have alanine, which is amino acid and we have threonine here. We're going to say we're gonna have the loss of water. So if we look at this, the loss of water, we would lose an this oxygen here and we'd lose two hydrogens here from the NH three group, right? So we have the loss of water here here, we show this arrow, this arrow that's pointing up shows that we have the loss of water. So it's leaving the two structures, what's left behind combined together to give us our peptide bond. So we lost this oxygen, we lost two hydrogens, meaning that nitrogen still has one H on it. So that, that's why it's still here. We didn't touch anything in terms of this carbon hill group. So it's still intact. The bond that they form is a result of them losing water. So now we have a dipeptide and we show this by giving the three letter code for each amino acid connected to each other by a hyphen. This shows that they are now connected together. So this hyphen here can represent this peptide bond between the two amino acids. Now, here we're going to say that the number of amino acids and peptides is indicated by prefixes. So we know die try tetra. Here, we're going to say that a polypeptide is a peptide consisting of larger number of amino acid residues. And remember a residue is just an individual amino acids contained within a peptide. Here, we call this a dye peptide dye because it's two amino acids connected by one peptide bond. If we had three amino acids, then it'd be a tripeptide. If we have four amino acids via petra peptide. If we have beyond that, then we can start talking about um it being a more complicated chain of amino acids connected by peptide bonds, right? But just remember we've seen something like this before, when we talked about the formation of a mi in earlier chapters. Now we're relating it to the connection of two different amino acids to one another, right? So just remember a peptide is two aminos connected by a peptide bond.
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example
Peptides Example 1
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Circle all peptide bonds and amino residues in the following heter peptide. All right. So remember a peptide bond is basically an am my bond. So we're gonna look for where we have a carbon meal, single bonded to a nitrogen. If we take a look, here goes one of them, this isn't a my bond. It goes a carbon carbon connected to a nitrogen. There goes another one and then their goals are last one here. So we have three peptide bonds. They say that it's a tetrapeptide. So that means we have four peptides connected to one another. So remember this would represent one peptide. Remember the amide bond is what connects two different peptides or two different amino acids to one another. So this is one. Here goes a second one. We're gonna cut the amide bond. That's a second. Then here this is another one. There goes another one, we should be circling it. But just for us to see me tracing where the peptide is. And then finally, we have this last one here. So this represents our four peptides involved
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concept
Drawing & Naming Peptides Concept 2
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Now, when it comes to drawing and naming peptides, remember that every peptide has directionality. What we mean by that is that we look at it from the N terminus to the C terminus N. Now when we say N terminus, this is just the residue with the free amino group. And when we say C terminus, this is the residue with the free carboxyl route that when drawing or naming always arrange from left to right and have it in N terminus to C terminus. When looking at a peptide. If we take a look here, we have our N terminus on the left. And that's because the free amino group is on the left side here on that end. And then they're connect it's connecting to another amino acid with this peptide bond here. And this is the C terminus because the carboxyl group is on this end, right. So we're looking at this structure, this peptide two amino acid is connected by peptide bond. And we're looking on the left side, we have our N terminus end and on the right side, we have our C terminus end. He this directionality in mind whenever you're naming or writing a pep time.
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example
Peptides Example 2
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Draw dipeptide structure consisting of giving amino acids in the following order. Next, we have to name the dipeptide using the three letter codes separated by hyphens. All right. So here, remember we have to write this in terms of N terminus to c terminus. So that would mean that the amino acid on the left side, it's going to be that it's carboxyl root will be interacting with the amino group of the amino acid on the right. Remember this is a condensation reaction where we're gonna have the loss of water. So we're gonna lose the oxygen from the carboxyl group and two hydrogens from the amino group. This is where the water is being lost. After that, everything left behind will come together to form our dipeptide structure. So here we're gonna draw this, we have our benzing ring with our oh, we have it connected to this ch two here which is connected to this carbon with the NH three positive. Next, we have here our, our box over and here I'm gonna draw the peptide bond here in red. It's connected now to this nitrogen which still has one of its hydrogens and it's still connected to all this stuff here. So ch two and then we have s each year and then we have the carboxy group here. So this would be our dipeptide structure. Now, what we need to do is we need to basically give the three letter code. So if we take a look at this, this amino acid on the right is easy to spot because it has an S A group which is unique to cysteine. We know s's three letter code is cys based on its first three letters. This one here has an oh group. It is a polar group. So remember this one is tyro, it's three letter code is Tyr again based on its first three letters that mean that this dipeptide that we have here would be Tyr hyphen cys. So this would be the dipeptide name using our three letter code and this would be the dipeptide structure.
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Problem
Problem
Draw a tripeptide structure consisting of following amino acids in following order. Name tripeptide using 3 letter codes.