Final answer:
The alpha (α)-helix and beta sheet structures are common folding patterns in polypeptides due to the formation of hydrogen bonds between amino acids.
Step-by-step explanation:
The alpha (α)-helix and beta sheet structures are common folding patterns in polypeptides due to the formation of hydrogen bonds between the non-R group portions of amino acids. In the alpha helix, hydrogen bonds form between every fourth amino acid and cause a twist in the amino acid chain. In the beta-pleated sheet, hydrogen bonds form between atoms on the polypeptide chain's backbone, creating pleats.