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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 hydrolysis. For this tetrapeptide, the number of possible sequences (primary structures) with `-NH_(2)` group attached to a chiral centre is :

Text Solution

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The four amino acids are :
(i) `H_(2)N-CH_(2)-COOH," Glycine (G)",`
(ii) `CH_(3)underset(CH_(3))underset("| ")"CH"-underset(NH_(2))underset("| ")"CH"-COOH: "Valine (V)"`
(iii) `CH_(3)underset(NH_(2))underset("| ")"CH"-COOH : " Alanine (A),"`
(iv) `C_(6)H_(5)-CH_(2)-underset(NH_(2))underset("| ")"CH"-COOH:" Phenyl alanine (P)"`
Since (A) is at the end, and G does not contain a chiral centre, then all tetrapeptides begin either with V or P. Thus, different options with `-NH_(2)` group attached to a chiral centre are :
(i) VPGA (ii) VGPA (ii) PVGA (iv) PGVA.
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