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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Problem of the Week Archive => Topic started by: Borek on November 19, 2012, 03:03:07 PM

Title: Problem of the week - 19/11/2012
Post by: Borek on November 19, 2012, 03:03:07 PM
Trivial, but I want to check something :)

Which of these two tripeptides will be not found between products of a natural polipeptyde hydrolysis:

A:
OC(=O)C(N)CCC(=O)NC(CS)C(=O)NCC(=O)O

B:
OC(=O)CCC(N)C(=O)NC(CS)C(=O)NCC(=O)O
Title: Re: Problem of the week - 19/11/2012
Post by: digchick21 on November 22, 2012, 09:58:18 AM
A
Title: Re: Problem of the week - 19/11/2012
Post by: Borek on November 22, 2012, 10:28:48 AM
Any explanation?
Title: Re: Problem of the week - 19/11/2012
Post by: DrCMS on November 22, 2012, 11:05:46 AM
I'd say B beacuse A is a tripiptide of three standard amino acids Asn-Cys-Gly while B is synthetic AA-Cys-Gly.
Title: Re: Problem of the week - 19/11/2012
Post by: Schrödinger on November 22, 2012, 03:00:59 PM
A has Cys and Gly but I dont think it has the Asn moiety. A is Glu-Cys-Gly, isn't it?
Title: Re: Problem of the week - 19/11/2012
Post by: digchick21 on November 23, 2012, 05:17:27 AM
"A" isn't a natural polypeptide, in that it doesn't follow the usual joining of the peptide bond:

NH-C(R)-CO-NH-C(R)-CO-NH-C(R)-COOH

Instead the first amino acid in "A" Glutamate is joined to the next amino acid, Cysteine through its R group unlike that in "B" which follows the normal pattern.
Title: Re: Problem of the week - 19/11/2012
Post by: AWK on November 23, 2012, 06:01:29 AM
GSH is quite natural but is not synthesized using peptide pathways
Title: Re: Problem of the week - 19/11/2012
Post by: Borek on November 23, 2012, 06:14:03 AM
Quote from: digchick21 on November 23, 2012, 05:17:27 AM
"A" isn't a natural polypeptide, in that it doesn't follow the usual joining of the peptide bond:

NH-C(R)-CO-NH-C(R)-CO-NH-C(R)-COOH

Instead the first amino acid in "A" Glutamate is joined to the next amino acid, Cysteine through its R group unlike that in "B" which follows the normal pattern.

That's the answer I was looking for.