The helical structure of secondary protein is kept by the formation of _ among amino acid molecules in successive turns of the spiral:

Explanation

The secondary structure of proteins, such as the alpha helix, is stabilized by hydrogen bonds. These bonds form between the carbonyl oxygen of one amino acid and the amide hydrogen of another amino acid, four residues away, within the polypeptide chain. This bonding pattern results in a coiled or helical structure. Other bond types, such as ionic bonds and disulfide bonds, contribute to the stabilization of proteins but are more relevant to tertiary and quaternary structures. Peptide bonds, while crucial for connecting amino acids, are fundamental to the primary structure and do not influence the secondary helical structure.