Draw the hexapeptide Asp-Gly-Phe-Leu-Glu-Ala in linear form showing all of the atoms, and show (using dotted lines) the hydrogen bonding that stabilizes this structure if it is part of an α-helix.

Question

Accepted Answer

Welcome back, everybody. Here's our next problem sketch the structural formula of the penda peptide. And then the sequence is listed with the three letter abbreviations for the amino acids tyrglyglyphemet in linear form and show the hydrogen bonding that stabilizes the structure if it forms an alpha helix. So our first step will be to look up the R groups of our amino acids so that we can draw out those structures. So we'll uh give everyone a second, look those up and I'll paste them on here. So let's start with our backbone of the first amino acid. So if we start on the left with our N terminus H two N and that's bonded to the alpha carbon, she's bonded to the carbon carbon hydrogen on the alph, the carbon. And then that has the peptide bond to the nitrogen of the next amino acid. I'm going to highlight the peptide bond in blue just to keep track of where I'm transitioning to another amino acid. And then I'll draw the R groups in red again, helps just keep this straight. So my first amino acid is terrace and I can see that the R group for terrace is CH two and then a benzene ring and then a hydroxy group in the paras position from that CH two. So extending down from my alpha carbon, I'll drive C two and then the benzene ring and then the hydroxy group and note that it says to put it in a linear form. So I'm just drawing these all kind of going across in a straight line rather than that zigzag zigzag that shows the bonding angles a little more accurately. So I've got my first amino acid, I'm onto the amino group of the second. So I've got the NH then we'll put C H that's my alpha carbon carbonel group and then again, the NH of the next amino acid. So highlight that peptide bond in blue. Now I'm on to glycine and glycine has just a hydrogen atom for its R group. So all I have to do is change the I have the ch for my alpha carbon make that CH two, the second hydrogen is the R group for that amino acid. So very simple. So I've gone on to the third amino acid amino group. So NH ch my alpha carbon carbonel group and NH for my next amino acid highlight that peptide bond. Now I'm on to another glycine. So same thing, I'm just going to put a two subscript on that hydrogen with the alpha carbon. So I just have NHCH two C double bonded to the O and then the peptide bond to the next amino acid. So I've got my two glycine. Now on to my next amino acid, I have the NH bonded to the alpha carbon. So ch bonded to the carbonel group and then the NH for my next amino acid, I like that peptide bond. So this amino acid after the two glycine I have phe which is be alanine and that is CH two and then a benzene ring. So I will draw that in red coming from the alpha carbon. So coming down from the alpha carbon, I have CH two and then a benzene ring. So similar to that terrace but no hydroxy group. So now let's keep track of how far we've gone before we add on more amino acids. I have just one more amino acid left. So I'm al almost at my C terminal. So I've added on my NH. So I won't add on another peptide bond after this one. So I have the NH add on my alpha carbon. So ch add on my Carbone group. This is the C terminal. So instead of a nitrogen from the carbon group, I have an oh bonded to it. That carboxylic acid at the end of my polypeptide chain, I just have to add my R group, this is met or methionine. So our group is CH two CH two sch three. So add that coming down from the alpha carbon, CH two CH two, that carbon has a bond to a sulfur atom which has a bond to another carbon, which is ach three group. So it kind of looks like I only have three R groups because my glycine just has that extra hydrogen. So now I have the polypeptide chain, five peptides in it. And all that's left is I need to show the hydrogen bonding that stabilizes the structure if it forms an alpha helix, while the alpha helix are formed by a hydrogen bond, so that hydrogen bond is between the carbonyl oxygen. And so the carbon oxygen of one amino acid and the amid hydrogen that is four residues farther along the backbone. So let's pick our first carbon hydrogen here. I'll put a little red arrow to point it out. There we go and we want to go to the amid hydrogen that is four residues farther along the backbone. So we're here in residue number one, which is tyrosine and then four residues further along 1234 to our last methionine. So let's find the amid hydrogen and armine. Remember the nitrogen is the first atom in the backbone. So we go all the way to our last amino acid and here is its hydrogen right next to it. So we just put a dotted line to signify a hydrogen bond. And I'll put that between the oxygen of this carbon and just draw this sort of dotted arc down the molecule to that amid hydrogen. And you could see where this can will cause this protein chain or peptide chain to twist around in a helical form with these bonds between every fourth residue that between the carbon oxygen and the amid hydrogen, keeping it twisting around. So we've given the formula of this polypeptide and we sketched our hydrogen bond highlight that in yellow from our amid or our carbon oxygen to the avid hydrogen. That's four residues ahead of it. See you in the next video.

Draw the hexapeptide Asp-Gly-Phe-Leu-Glu-Ala in linear form showing all of the atoms, and show (using dotted lines) the hydrogen bonding that stabilizes this structure if it is part of an α-helix.

Verified video answer for a similar problem:

Key Concepts

Peptide Structure

Hydrogen Bonding in α-Helices

Linear vs. Tertiary Structure