The secondary structure of a protein is maintained by intermolecular and intramolecular hydrogen bonding of amide groups. The secondary protein structure was proposed to have either an alpha helix or beta pleated sheet by Linus Pauing and Robert Cory in 1951.
Pauling and Cory made their proposal after taking X-ray photographs and building molecular models. The alpha helix structure, the polypeptide chain, is coiled like a spring and can be either right or left handed. In the beta pleated sheet structure, the protein chains are aligned in a side by side manner next to every other protein chain in the opposite direction.