Peptide Bonds in Polypeptides

Steps:

• A polypeptide consists of amino acids linked end-to-end.
• A peptide bond forms between the carboxyl group of one amino acid and the amino group of the next.
• In a linear chain, bonds connect consecutive amino acids only.
• For n amino acids, bonds occur between n-1 pairs.

Why A is correct:

• By definition, a peptide bond joins two amino acids, so n amino acids form exactly n-1 peptide bonds in a chain.

Why the others are wrong:

• B: Equals n, but each bond links two amino acids, requiring one fewer bond than amino acids.
• C: n+1 exceeds the possible connections in a linear polypeptide chain.
• D: n+2 implies impossible extra bonds beyond sequential linkages.

Final answer: A