Properties of Peptide Bonds

Steps:

• Statement 1 is false: Peptide bonds link amino acids, which vary in proteins and are not always identical.
• Statement 2 is true: The peptide bond formula (-CO-NH-) includes four distinct atoms: C, O, N, H.
• Statement 3 is false: Peptide bonds undergo hydrolysis but require enzymes, acid, or base catalysis, not mere water addition.
• Statement 4 is true: Peptide bonds form the covalent linkages defining the linear sequence in protein primary structure.

Why D is correct:

• Peptide bonds are amide linkages (-CO-NH-) between amino acids, involving C, O, N, H atoms, and they constitute the backbone of protein primary structure per biochemical definitions.

Why the others are wrong:

• A includes false statements 1 and 3.
• B includes false statement 1.
• C omits "only," but includes correct 2 and 4 without excluding 1 and 3 explicitly.

Final answer: D