At what level of structure do alpha helices and beta sheets form?

Alpha helices and beta sheets are motifs that form within the secondary structure of proteins. Secondary structure refers to the local spatial arrangement of the amino acid backbone in a polypeptide chain, which is stabilized primarily by hydrogen bonds between the carbonyl oxygen of one amino acid and the amide hydrogen of another.

In the case of alpha helices, this helical structure is stabilized by hydrogen bonds that form between every fourth amino acid, creating a coiled shape. Beta sheets, on the other hand, consist of strands held together by hydrogen bonds, where the strands can be parallel or antiparallel. These structures are essential for the overall stability and function of proteins, as they contribute to the protein’s overall conformation.

Primary structure pertains to the linear sequence of amino acids, tertiary structure involves the overall three-dimensional shape of a single protein molecule, and quaternary structure refers to the arrangement of multiple protein subunits in a complex. Therefore, alpha helices and beta sheets are indicative of the secondary structural level, making the answer correct.