The secondary structure of a protein
or polypeptide is due to hydrogen bonds forming between an oxygen atom of
one amino acid and a nitrogen atom of another. There are two possible types
of secondary structure: an alpha helix and a beta sheet. In the case of an
alpha helix, the hydrogen bonding causes the polypeptide to twist into a helix.
With a beta sheet the hydrogen bonding enables the polypeptide to fold back
and forth upon itself like a pleated sheet.
