What characterizes the secondary structure of proteins?

The secondary structure of proteins is defined by the regular patterns of coils or folds that occur along the polypeptide chain. These structures are primarily formed through hydrogen bonds between the backbone atoms in the protein. The most common types of secondary structures are alpha helices and beta pleated sheets.

The specific sequence of amino acids pertains to the primary structure of a protein, which determines how the secondary structure will form but does not describe the secondary structure itself. The number of polypeptide subunits refers to the quaternary structure of proteins, which involves how multiple polypeptide chains interact and assemble into a larger functional unit. Hydrophobic interactions among R groups are relevant to the tertiary structure, influencing how the protein folds into its three-dimensional shape but do not directly define the repetitive patterns of the secondary structure. Therefore, the correct characterization of the secondary structure is indeed the presence of these regular patterns of coils or folds.