Which type of bond predominates in the secondary structure of proteins?

• A. Covalent bonds
• B. Hydrogen bonds
• C. Ionic bonds
• D. Disulfide bonds

Answer: (B)

Hydrogen bonds between the backbone amide and carbonyl groups are the main force that stabilizes protein secondary structure. In alpha helices, a hydrogen bond forms between the carbonyl oxygen of one residue and the amide hydrogen of a residue four positions ahead, creating a regular helical pattern. In beta sheets, hydrogen bonds occur between carbonyls and amides on adjacent strands, aligning them into a pleated sheet. The peptide bonds themselves link amino acids, but they don’t create the repeating geometry of helices or sheets. Disulfide bonds and ionic interactions involve side chains and are more pertinent to stabilizing the overall fold (tertiary or quaternary) rather than the regular backbone-based secondary motifs.