A tetrapeptide has a -COOH group on alanine. | vedclass

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(A) The tetrapeptide has alanine $(Ala)$ at the $C$-terminal position because the $-COOH$ group is on alanine.The remaining three amino acids are glyc

Vedclass · Accepted Answer

$4$

Vedclass · Answer

(A) The tetrapeptide has alanine $(Ala)$ at the $C$-terminal position because the $-COOH$ group is on alanine.The remaining three amino acids are glycine $(Gly)$,valine $(Val)$,and phenylalanine $(Phe)$.For the $-NH_2$ group to be attached to a chiral center,the $N$-terminal amino acid must be chiral.Glycine is achiral (optically inactive),so it cannot be at the $N$-terminal position.Therefore,the $N$-terminal position can be occupied by either valine $(Val)$ or phenylalanine $(Phe)$.If $Val$ is at the $N$-terminal,the possible sequences are:$Val-Phe-Gly-Ala$$Val-Gly-Phe-Ala$If $Phe$ is at the $N$-terminal,the possible sequences are:$Phe-Val-Gly-Ala$$Phe-Gly-Val-Ala$Total number of possible sequences = $2 + 2 = 4$.

$A$ tetrapeptide has a $-COOH$ group on alanine. This produces glycine $(Gly)$,valine $(Val)$,phenylalanine $(Phe)$,and alanine $(Ala)$ on complete hydrolysis. For this tetrapeptide,the number of possible sequences (primary structures) with the $-NH_2$ group attached to a chiral center is:

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