Question

A tetrapepetide has – COOH 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 sturctures) with – $N{H}_2$ group attached to a chiral centre is ___

Answer 1

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 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.