Stick model showing the polypeptide backbone and hydrogen bonds, i.e. green lines between the two heavy atoms of the peptide hydrogen bond, C=O···H–N.
Each residue in the helix is involved in two hydrogen bonds (except for the residues at the ends). These hydrogen bonds are nearly parallel to the axis. However, the hydrogen bond geometry is not perfect, as the peptide N-H is not directed precisely toward the lone-pair electrons of the oxygen atom.