What characterizes the secondary (2°) structure of proteins?

The secondary structure of proteins is primarily characterized by the folding and coiling of the polypeptide chain into specific patterns, namely alpha-helices and beta-sheets. This structural organization arises due to hydrogen bonding interactions between the backbone amide and carbonyl groups of the amino acids in the protein chain. These bonds create stable formations, allowing regions of the polypeptide to twist into a helical shape or form flat sheets.

This distinction is important because the secondary structure is one of the fundamental levels of protein structure, setting the stage for higher levels of organization—tertiary and quaternary structures, which involve more complex folding and interactions amongst multiple polypeptides. Understanding the nature of these hydrogen bonds helps explain how proteins maintain their shape and function, as these structures contribute significantly to their overall stability and biological activity.