JEE Advanced 2013 · Paper 1 · Chemistry Q37

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ChemistryInteger+4 / -1Question 37 of 60

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 $\ce{-NH2}$ group attached to a chiral center is

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Answer and worked solution

Official answer: 4

Constraints. Ala is C-terminal (fixed in position 4). The N-terminal residue must have its NH₂ on a chiral carbon, so it cannot be Gly: it is Val or Phe.

Count. 2 choices for position 1, then the other two residues in 2! ways: 4 sequences.

Answer: 4

Topics:Amino acids and proteins Optical isomerism and chirality

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JEE Advanced 2013 · Paper 1, Chemistry question 37