DNA Double Helix Structure Announced

Setting the scene

By 1953, scientists knew DNA carried genetic information, but not how. Oswald Avery had shown DNA was the 'transforming principle' in 1944, but its structure was unknown. Linus Pauling had discovered the alpha helix structure of proteins in 1951, and many thought DNA was also a triple helix. At Cambridge University, American James Watson and English Francis Crick were racing against Pauling and Maurice Wilkins and Rosalind Franklin at King's College London, who were using X-ray crystallography to study DNA.

What happened

The breakthrough came from Franklin's Photo 51, an X-ray diffraction image taken in May 1952 that showed DNA's helical structure. Wilkins showed the photo to Watson without Franklin's permission in January 1953. Watson and Crick, using Franklin's data and their own model building, realized DNA was a double helix with two antiparallel strands. The key insight was base pairing—adenine pairs with thymine, guanine with cytosine—explaining how DNA replicates. On February 28, 1953, Crick announced in the Eagle pub in Cambridge, 'We have found the secret of life.' They published in Nature on April 25, 1953, in a 900-word paper.

Why it still matters

The double helix discovery revealed the molecular basis of heredity and launched molecular biology. It explained how genetic information is stored and copied, enabling genetic engineering, DNA sequencing, and the Human Genome Project. Watson, Crick, and Wilkins won the 1962 Nobel Prize; Franklin had died in 1958 and was not eligible. The discovery's history remains controversial due to Franklin's uncredited contribution. The double helix became the icon of modern science, appearing on stamps and logos. It fundamentally changed medicine, forensics, and our understanding of life, making possible everything from paternity tests to CRISPR gene editing.

Background

Rosalind Franklin's X-ray data was crucial to the discovery.