Fill in the blanks with the primary sequence of the peptide. U...

Question

Fill in the blanks with the primary sequence of the peptide. Use the 1-letter codes. Circle all the α-carbons.

Diagram of a peptide showing primary structure with α-carbons circled and 1-letter codes for amino acids.

Accepted Answer

So this practice problem wants us to fill in the blanks below with the primary sequence of the peptide in the figure, and it says to use the one letter codes and to circle all of the alpha carbons. And recall that the alpha carbon is just the central carbon atom of a amino acid which, the R group is attached to. And so over here on the far left, what we have is our 4 mnemonics to help us, memorize the 20 amino acids and the 4 groups that they fall under. And so, the first group that we have are the non polar amino acids and our mnemonic is just GAV LIMP. The second group that we have is the aromatic amino acids and it's just fat young whippersnappers to remember those. And then our third one is the polar amino acids and this is Samus Team Crafts New Quilts. And then our last one are the charged amino acids and the mnemonic is dragons eat knights riding horses. And so this is gonna help us identify each of the r groups. So notice with our peptide over here, the first, group that we have is the amino group, so we have a free amino group on the far left. And so notice our amino group is attached to a carbon and this is an alpha carbon. And the reason we know it's an alpha carbon is because it's attached to an R group. And notice that this specific R group has a carboxyl group on it, and so it has a carboxylic acid and that means that it must be acidic. So that means that it's gotta be one of our acidic, negatively charged acidic amino acids. So it's either aspartic acid or glutamic acid. And because this is just alanine with one carboxyl group here, this must be aspartic acid. So this be d here, for aspartic acid, which, remember, is just alanine with a carboxyl group. So because this r group right here is aspartic acid's r group, we can put a d here up here for aspartic acid. So then next, what we have in our, chain is a carbonyl group, and notice that the carbonyl group is attached to a nitrogen atom. So we've got a carbonyl attached to a nitrogen, which means that this bond right here is an amide linkage and this is our first peptide bond. And then we have a nitrogen attached to another carbon and this carbon right here is another alpha carbon because we have an r group extending off of it. And this r group, notice that it has a single, carbon atom with 3 parts on it. So this must be threonine. So the 3 parts are a hydrogen, a methyl group, and a hydroxyl group on its only carbon. And so, threonine is over here with our mnemonic. And so, threonine's structure is really based off of serine structure. So remember that even though Santa and his team, serine and threonine, they know that alcohol is a serious threat. So, serious threat is for threonine and, serine having alcohol groups. So notice there's an alcohol group here, an Oh group. That it's okay for San and his team to have alcohol in moderation while they're crafting their new quilts. So what we can see is that threonine is really just going to be searing with an extra methyl group, and that's what we see. And so because this R group right here is threonine's R group, we can put a t here to represent threonine. So then, again, what we have is our carbonyl group which is next and it's attached to another nitrogen. So this is another amide linkage right here and it's our second peptide bond. And then what we have is our carbo our next alpha carbon because, again, it's attached to an R group. And notice that this R group has a benzene ring in it and because it has a benzene ring, we know that it's got to be one of our aromatic amino acids. And when we look closely, what we'll see is that it's really just alanine with a phenyl group. So alanine with a phenyl group must mean that this is phenylalanine, which is F. And so, because this R group right here is phenylalanine's R group, we can put an F as our 3rd amino acid residue in this chain. And then, what we see is we got another carbonyl group and another nitrogen attached to it. So this is another amide linkage here in our 3rd peptide bond. And so notice that it's attached to another alpha carbon and we've got another r group coming down right here. And notice that there's an a positively charged, amino group on this alpha carbon. So that must mean that we have a positively charged basic amino acid, and it's gotta be one of our knights riding horses because knights riding horses, fighting dragons are very positive. They're trying to save the day and so it's really long r group right here and it looks like a knight sword. So this must be lysine, our knight here, our knight sword. So just like a knight sword, you try to poke somebody with, you think about the one letter code here and how many ends it has that you could really try to poke somebody with. And it's got 4 ends you could try to poke somebody with, which reminds us that there must be a 4 carbon start to to our chain with an amino group at the very end. And so, this is indeed lysine's R group. And so, because this is lysine's R group, we can put a k here to represent lysine at the very end. And then, notice that at the very end over here, what we have is just a free carboxyl group. And so essentially, what we've done is we've identified the primary sequence of the peptide from the n terminal end to the c terminal end using the one letter code. So this concludes this practice problem and I'll see you guys in our next one.

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Fill in the blanks with the primary sequence of the peptide. Use the 1-letter codes. Circle all the α-carbons.

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