Nucleic acid structure

Nucleic acid structure is the organization of DNA or RNA, from nucleotide sequence and backbone geometry to base pairing and three-dimensional folding. Its form enables information storage, molecular recognition, and biological activity.

Nucleotide: A molecule composed of a nitrogenous base, a sugar, and one or more phosphate groups. Nucleotides are the repeating units whose sequence and chemistry shape nucleic acids.
Watson–Crick base pairing: The canonical hydrogen-bonding pattern pairing adenine with thymine or uracil and guanine with cytosine. Complementary pairing holds many nucleic acid strands together.
B-DNA: The common right-handed DNA double helix found under physiological conditions. B-DNA is the familiar reference form for discussing DNA geometry.
X-ray diffraction: A method that infers material structure from the scattering of X-rays by ordered matter. Diffraction patterns supplied key constraints on DNA's helical dimensions.
DNA sequencing: Laboratory methods for determining the order of nucleotides in DNA. Sequence measurements reveal the primary structure from which higher forms arise.
Nucleoside: A nitrogenous base attached to a sugar, without a phosphate group. Nucleosides provide the base-and-sugar portion of each nucleotide.
Base stacking: Attractive interactions between neighboring nucleobases that contribute to nucleic acid stability and shape. Stacking helps stabilize helices beyond hydrogen bonds between paired bases.
A-DNA: A right-handed DNA helix that is shorter and wider than B-DNA. A-DNA illustrates how hydration and molecular context alter helical geometry.
Photo 51: An X-ray diffraction image of DNA produced by Raymond Gosling under Rosalind Franklin's direction. Its cross-shaped pattern strongly indicated a helical structure.
Cryogenic electron microscopy: A technique that images frozen biological specimens using an electron beam at cryogenic temperatures. It can resolve large nucleic-acid-containing assemblies in near-native states.

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