Bonds Stabilizing Protein Structures

Steps:

• Identify primary structure bonds: covalent peptide linkages between amino acids.
• Identify secondary structure bonds: hydrogen bonds between backbone carbonyl and amide groups.
• Identify tertiary structure bonds: ionic interactions (salt bridges) between charged side chains.
• Identify quaternary structure bonds: hydrophobic interactions between nonpolar side chains of different subunits.

Why B is correct:

• B accurately lists the primary bonds for each structure level per standard biochemistry definitions: covalent (primary), hydrogen (secondary), ionic (tertiary), hydrophobic (quaternary).

Why the others are wrong:

• A: Lists covalent for secondary (should be hydrogen) and confuses tertiary/quaternary bonds.
• C: Misplaces peptide (primary) and covalent (not secondary); hydrophobic is tertiary, not exclusive.
• D: Quaternary involves more than ionic only (includes hydrophobic, disulfide).

Final answer: B