Double helix

The molecular structure of DNA, in which two complementary nucleotide strands coil around a shared axis. The strands are held together by paired bases and run in opposite directions.

Watson–Crick base pairing: The hydrogen-bonding pattern in DNA that pairs adenine with thymine and guanine with cytosine. Complementary pairing holds the two strands together while preserving a template for copying.
Nucleotide: A molecule composed of a nitrogenous base, a sugar, and one or more phosphate groups. Nucleotides are the repeating units that form each strand of the helix.
Rosalind Franklin: A chemist whose X-ray diffraction studies revealed key structural properties of DNA. Her diffraction data constrained the dimensions and helical form of DNA.
Central dogma of molecular biology: The framework describing the usual flow of sequence information from DNA to RNA to protein. The helix became the molecular starting point for explaining gene expression.
A-DNA: A right-handed DNA helix with a shorter, wider form than B-DNA. It shows that DNA’s double helix can shift geometry under different conditions.
Antiparallel (DNA): The arrangement in which DNA’s two strands run in opposite chemical directions. Opposite strand orientation is a defining feature of the double helix’s geometry.
DNA: A molecule that stores hereditary information in sequences of nucleotides. The double helix is DNA’s characteristic molecular structure.
Maurice Wilkins: A physicist who used X-ray diffraction to investigate the structure of DNA. His DNA studies contributed evidence and context to the structural model.
Genetic code: The rules by which nucleotide sequences specify amino acids in proteins. DNA sequence in the helix carries the information interpreted through this code.
Z-DNA: A left-handed DNA helix with a zigzag-shaped sugar-phosphate backbone. Its handedness contrasts with the familiar right-handed double helix.

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