Biomolecules and Chemistry in Everyday Life - Result Question 30
####31. A tetrapeptide has - $COOH$ group on alanine. This produces glycine (Gly), valine (Val), phenyl alanine (Phe) and alanine (Ala), on complete hydrolysis. For this tetrapeptide, the number of possible sequences (primary structures) with $-NH _2$ group attached to a chiral centre is
(2013 Adv.)
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Solution:
- PLAN A peptide linkage is hydrolysed to two free amino acids.
$C^{*}$ is chiral carbon tetrapeptide has four amino acids joined by three peptide linkage.
- $COOH$ group is on alanine part, thus it is at fixed $C$-terminal position in each combination.
Glycine is optically inactive thus it cannot be on the Nterminal side. Thus, possible combinations are
Phe-Gly-Val-Ala, Phe-Val-Gly-Ala, Val-Gly-Phe-Ala, Val-Phe-Gly-Ala
Thus, in all four combinations are possible.
