Peptide Bond Formation Involves Dehydration Synthesis

Steps:

• Peptide bonds form between the carboxyl group (COOH) of one amino acid and the amino group (NH₂) of another.
• This reaction eliminates water: the OH from COOH and H from NH₂ combine to form H₂O.
• The H atom from the NH₂ group's nitrogen contributes one hydrogen to H₂O.
• The H atom from the OH group of COOH contributes the other hydrogen to H₂O.

Why B is correct:

• Option B pairs the H on the incoming amino acid's NH₂ (label 1) with the H on the first amino acid's COOH (label 6), matching the dehydration reaction's H₂O components.

Why the others are wrong:

• A: Label 4 is likely on COOH oxygen, but pairs incorrectly with 1; water needs H from NH₂ and OH's H.
• C: Labels 3 and 5 are probably on side chains or alpha carbons, not involved in bond formation.
• D: Label 2 is likely alpha hydrogen, irrelevant to water production; 4 mismatches as above.

Final answer: B