A tetrapeptide, made up of natural amino acids, has alanine as the N-terminal residue which is coupled to a chiral amino acid. Upon complete hydrolysis, the tetrapeptide gives glycine, alanine, phenylalanine and leucine. The number of possible sequences of the tetrapeptide is ____ .
Answer
Answer (as printed): 4
The options are missing from the source scan for this question, so there is nothing here for this letter to point at. The letter is what the book printed.
Explanation
Answer: 4 — Ala is at the N-terminus, and position 2 must be a chiral amino acid (Phe or Leu; Gly is achiral): 2 choices. The remaining two residues fill positions 3–4 in 2 ways. 2 × 2 = 4.