1. Tardigrade
  2. Question
  3. Chemistry
  4. 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

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Q. 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

JEE AdvancedJEE Advanced 2013Biomolecules

Solution:

PLAN A peptide linkage is hydrolysed to two free amino acids.
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$C^{*}$ 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 $N$ - terminal 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.