Which of the following describes the backbone interactions in protein secondary structures?

The correct answer highlights that only hydrogen bonds are responsible for forming the stable structures in protein secondary structure, specifically in alpha helices and beta sheets. In these secondary structures, hydrogen bonds form between the carbonyl (C=O) group of one amino acid and the amide (N-H) group of another amino acid that is typically located four residues down in the case of alpha helices or between strands in beta sheets.

This means that the hydrogen bonding is crucial in stabilizing these structures, allowing them to maintain their specific conformations. The formation of hydrogen bonds occurs because of the polar nature of the peptide bonds found in the protein backbone, which facilitates this interaction.

Ionic bonds, while important in stabilizing the overall three-dimensional structure of proteins, do not specifically contribute to the formation of the secondary structure elements on their own. The predominance of hydrogen bonds in this context underscores their vital role in providing stability and structural integrity to secondary structures in proteins.