Final answer:
Alpha helices and beta sheets in proteins are stabilized by hydrogen bonds between the oxygen of carbonyl groups and the nitrogen of amino groups, either within the same polypeptide chain or between different chains.
Step-by-step explanation:
Alpha helices and beta sheets, often referred to as beta pleated sheets, are secondary structures in proteins that are held together by hydrogen bonds. Specifically, these bonds form between the carbonyl group's oxygen of one amino acid and the amino group's nitrogen of another, which can be part of the same polypeptide chain or between different chains. In an alpha helix, the R groups of the amino acids stick out from the helix, allowing the helix to maintain its shape due to hydrogen bonding between every fourth amino acid. In contrast, the beta pleated sheet is characterized by regions of polypeptide chains lying side-by-side, which may be parallel or antiparallel to each other, and hydrogen bonds form between the chains to hold the sheets together.