Final answer:
The α-helix and β-pleated sheet are secondary structures of proteins that result from hydrogen bonding within the peptide backbone.
Step-by-step explanation:
The α-helix and β-pleated sheet are both common polypeptide forms found in the secondary structure of proteins. These structures form because of hydrogen bonding between carbonyl and amino groups in the peptide backbone of the polypeptide chain. In the α-helix, every helical turn contains 3.6 amino acid residues, with the side chains (R groups) extending outwards from the helix. The β-pleated sheet consists of polypeptide chains aligned parallel or antiparallel, and is stabilized by hydrogen bonds between the carbonyl oxygen and the amino hydrogen atoms of the backbone. Certain amino acids have a propensity to form either the α-helix or the β-pleated sheet, greatly influencing the structure and function of the protein.