Biomolecular structure is the intricate folded, three-dimensional shape that is formed by a
protein,
DNA, or
RNA molecule, and that is important to its function. The structure of these molecules is frequently decomposed into primary structure, secondary structure, tertiary structure, and quaternary structure. The scaffold for this structure is provided by secondary structural elements that are
hydrogen bonds within the molecule. This leads to several recognizable "domains" of
protein structure and
nucleic acid structure, including secondary structure like
hairpin loops, bulges and internal loops for nucleic acids, and
alpha helices and
beta sheets for proteins.