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title: The Structure of DNA
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On 25 April 1953, the journal *Nature* published a one-page paper by James Watson and Francis Crick proposing that DNA is a double helix — two strands winding around each other, with paired bases forming the rungs of a twisted ladder. The structure immediately suggested how genes are copied and passed on, and it founded molecular biology. The model rested heavily on the X-ray crystallography of Rosalind Franklin, whose contribution went largely uncredited for decades.

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  **At a glance** — 25 April 1953 · Cambridge, England · **Status:** historical
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## What happened

Working at the Cavendish Laboratory in Cambridge, Watson and Crick built physical models constrained by the known chemistry of DNA and by X-ray diffraction images — most decisively Franklin's "Photograph 51," taken at King's College London and shown to them without her knowledge. They deduced an antiparallel double helix in which adenine pairs with thymine and guanine with cytosine. Their *Nature* paper famously noted, with deliberate understatement, that the base pairing "immediately suggests a possible copying mechanism for the genetic material." Companion papers by Franklin and by Maurice Wilkins appeared in the same issue.

## Why it matters

The double helix explained, in one stroke, how hereditary information is stored, copied, and transmitted — turning genetics from an abstract study of inheritance into a molecular, mechanistic science. It launched the era of molecular biology and underpins everything from the genetic code and recombinant DNA to genome sequencing, forensics, and modern medicine. Few single insights have been as generative.

## Background — what led here

By the early 1950s, experiments had established DNA — not protein — as the carrier of heredity, and Erwin Chargaff had found that the amount of adenine matched thymine, and guanine matched cytosine. Linus Pauling had recently solved protein structures by model-building and was racing toward DNA. The decisive missing piece was high-quality X-ray data, which Franklin and Wilkins were producing at King's College London.

## Consequences

The discovery won Watson, Crick, and Wilkins the 1962 Nobel Prize in Physiology or Medicine; Franklin had died in 1958, and the prize is not awarded posthumously. The following decades cracked the genetic code, developed gene cloning and sequencing, and culminated in the Human Genome Project — and, more recently, CRISPR gene editing. The double helix is now among the most recognizable icons of science.

## Perspectives

The discovery is also a touchstone in debates over credit and gender in science. Franklin's X-ray work was essential, yet she was not named on the prize and her role was minimized — notably in Watson's memoir *The Double Helix* — before later scholarship restored her standing. Some historians frame the episode as brilliant synthesis; others as a cautionary tale about data used without consent and recognition withheld.

## Sources

1. J. D. Watson & F. H. C. Crick, "Molecular Structure of Nucleic Acids," *Nature* 171 (1953).
2. [Rosalind Franklin and the structure of DNA — Nature](https://www.nature.com/)
3. [The discovery of the double helix — Cold Spring Harbor DNA Learning Center](https://www.dnalc.org/)