Question

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 - NH₂ group attached to a chiral centre is___

Answer 1

PLAN A peptide linkage is hydrolysed to two free amino acids.

C’ is chiral carbon tetrapepetide 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.