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A tetrapeptide has -COOH group on alanin...

A tetrapeptide has `-COOH` group on alanine. This produces glycine (Gly), valine (Val), phenyl alanine (Phe) and alanine (Ala), on complete hydrolyses. For this tetrapeptide, the number of possible sequences (primary structures) with `-NH_(2)` group attached to a chiral centre is

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The correct Answer is:
4
Following combinations are possible for tetrapeptide
`{:("Val-Phe-Gly-Ala"),("Val-Gly-Phe-Ala"),("Phe-Gly-Val-Ala"),("Phe-Val-Gly-Ala"):}`
1. In all above sequences C-terminal is alanine.
2. Glycine is optically inactive amino acid, hence it should not be N-terminal so, only above combination are possible.
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