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Biomolecular structure
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<table><tbody><tr><td></td><td></td></tr></tbody></table> <p> Biomolecular structure is the intricate folded, three-dimensional shape that is formed by a <a href="/facts/Molecule/N9ljSfFq">molecule</a> of <a href="/facts/Protein/Jxmagu3E">protein</a>, <a href="/facts/DNA/nB89Iauz">DNA</a>, or <a href="/facts/RNA/HxPeNfNj">RNA</a>, and that is important to its function. The structure of these molecules may be considered at any of several length scales ranging from the level of individual <a href="/facts/Atom/FoQ4kGN5">atoms</a> to the relationships among entire <a href="/facts/Protein_subunits/HhuET9UP">protein subunits</a>. This useful distinction among scales is often expressed as a decomposition of molecular structure into four levels: primary, secondary, tertiary, and quaternary. The scaffold for this multiscale organization of the molecule arises at the secondary level, where the fundamental structural elements are the molecule's various <a href="/facts/Hydrogen_bond/85V86IIg">hydrogen bonds</a>. This leads to several recognizable <i>domains</i> of <a href="/facts/Protein_structure/BptnTs9X">protein structure</a> and <a href="/facts/Nucleic_acid_structure/U7sYh5pn">nucleic acid structure</a>, including such secondary-structure features as <a href="/facts/Alpha_helix/7CESPIYJ">alpha helixes</a> and <a href="/facts/Beta_sheet/B6mwwR6H">beta sheets</a> for proteins, and <a href="/facts/Hairpin_loop/GysAzrX5">hairpin loops</a>, bulges, and internal loops for nucleic acids. The terms <i>primary</i>, <i>secondary</i>, <i>tertiary</i>, and <i>quaternary structure</i> were introduced by <a href="/facts/Kaj_Ulrik_Linderstr%25C3%25B8m-Lang/NCoHwBAt">Kaj Ulrik Linderstrøm-Lang</a> in his 1951 Lane Medical Lectures at <a href="/facts/Stanford_University/JEQeF9z2">Stanford University</a>. </p>