Biomolecular structure is the intricate folded, three-
dimensional shape that is formed by a protein, DNA, or RNA
molecule, and which 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 which 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. Primary structure  In biochemistry, the
Primary structure of a biological molecule is the exact
specification of its atomic composition and the chemical bonds
connecting those atoms (including stereochemistry). For a
typical unbranched, un-crosslinked biopolymer (such as a
molecule of DNA, RNA or typical intracellular protein), the
primary structure