Peptide Bond Formation Between Amino and Carboxyl Groups

Steps:

• A peptide bond forms via condensation reaction, linking the carboxyl (COOH) group of one amino acid to the amino (NH2) group of another, releasing water.
• The first amino acid has two NH2 groups (1 and 2), so one of these acts as the nucleophile.
• The second amino acid has two COOH groups (3 and 4), so one of these acts as the electrophile.
• The bond specifically involves one NH2 from the first and one COOH from the second, as per standard biochemistry.

Why B is correct:

• Option B pairs an NH2 group (e.g., 2) with a COOH group (e.g., 3), matching the definition of peptide bond formation between dissimilar functional groups.

Why the others are wrong:

• A pairs two NH2 groups, which cannot form a peptide bond as both are nucleophilic.
• C pairs two COOH groups, which cannot form a peptide bond as both are electrophilic.
• D pairs mismatched or incorrect labels, violating the amino-carboxyl linkage rule.

Final answer: B