By Ivan Noble
BBC News Online science staff
Fifty years ago, on 25 April 1953, the science journal Nature published a paper by James Watson and Francis Crick describing their model of the structure of DNA.
Watson and Crick were elated at finding the "secret of life", but it took the rest of the scientific world several years to recognise the true significance of their double helix model.
Watson and Crick's model is now in the Science Museum in London
Image courtesy Science Museum
The pair from Cambridge University went on to receive a Nobel Prize for their work, together with Maurice Wilkins of King's College London, who carried out key experiments on DNA.
A fourth researcher whose work was crucial to the discovery, Rosalind Franklin, died of cancer before her role was recognised.
THE DNA MOLECULE
The double-stranded DNA molecule is held together by chemical components called bases
Adenine (A) bonds with thymine (T); cytosine(C) bonds with guanine (G)
Groupings of these letters form the "code of life"; there are about 2.9bn base pairs in the human genome wound into 24 distinct bundles, or chromosomes
Written in the DNA are 30,000-40,000 genes which human cells use as templates to make proteins; these sophisticated molecules build and maintain our bodies
DNA was shown to be the mystery molecule which carries genetic information from generation to generation by researchers working during World War II.
But until Watson and Crick made their breakthrough, no-one knew what DNA looked like or how it worked.
From helices to genomes
The 50 years which followed their discovery ended with the completion of the sequencing of the human genome.
This was a massively ambitious, industrial-scale project to identify every single letter in the almost three billion letter genetic code of human DNA.
Scientists, including six Nobel Laureates, met in London on Wednesday to mark the anniversary.
James Watson, now President of the renowned Cold Spring Harbor Laboratory, gave a speech in which he appealed for scientists to engage with the public more and stand up for their right to carry out research in areas which have aroused public controversy.