Secondary structures stabilized by hydrogen bonds

Steps:

• Define secondary structure as local folding patterns like alpha helices and beta sheets in proteins.
• Identify key interactions: hydrogen bonds form between backbone carbonyl (C=O) and amide (N-H) groups.
• Distinguish from primary structure (peptide bonds) and tertiary (ionic, hydrophobic, disulfide bonds).
• Conclude that only hydrogen bonds maintain secondary structure integrity.

Why C is correct:

• Secondary structures rely solely on hydrogen bonds for stabilization, as per protein folding principles.

Why the others are wrong:

• A includes 2 and 3, which involve tertiary interactions like ionic or hydrophobic bonds.
• B includes 3, incorrectly adding non-secondary bonds such as disulfide bridges.
• D excludes 1, omitting the essential hydrogen bonds.

Final answer: C