3D Structure Of DNA: Deoxyribonucleic Acids

On 25 April 1953, a paper appeared in Nature that was to transform the life sciences from biochemistry and agriculture, to medicine and genetics. James Watson, a young American and an Englishman, Francis Crick, then at Cambridge University proposed a double helical model for the structure of DNA (deoxyribonucleic acid) molecule. (3)

Crick and Watson used model building to reveal the renowned double helix of DNA, but the X-ray crystallographic data of Rosalind Franklin ( Picture 1 on the Left) and Maurice Wilkins at King's College, London, were crucial to the discovery that allowed Watson and Crick to work out the 3D structure of DNA which was found to be a double helix.(1) After the discovery of the nuclein by Swiss biochemist Friedrich Miescher

The Austrian chemist, Erwin Chargaff established the paper chromatography of nucleic acids, using this to determine how much of each of the component nucleotides was contained in a DNA sample. He rapidly demolished Levene's tetranucleotide hypothesis. Each species differed in the amount of A, C, G and T - but within the species, the proportions of each are identical, no matter which tissue the DNA is extracted from. It was just what might be expected for a molecule that is the biological signature for the

At King's College, London, Maurice Wilkins was intrigued by the long fibres that DNA forms when it is pulled out of watery solutions with a glass rod, wondering if this meant there was some regularity to its structure. He produced more X-ray pictures, using makeshift apparatus the like of which is hard to imagine nowadays. In 1951, Wilkins was joined by Rosalind Franklin, a British physical chemist who already had an international reputation for her work on the X-ray crystallography of coals. She set about building a dedicated X-ray lab at King's and was soon producing the best images ever of DNA. These led her to the idea that maybe the DNA molecule was coiled into a helical shape.

Linus Pauling, the US chemist, and author of The nature of the chemical bond, began to think along similar lines. After all, Pauling had already discovered helical motifs in protein structures. Around this time, Francis Crick - with a background in maths and physics, and the younger James Watson, with expertise in the molecular biology of phage (viruses that infect bacteria, then used as a laboratory tool for genetic studies), joined forces at the Cavendish Laboratory in Cambridge, (Picture 2 on the Left) intent on cracking the DNA structure themselves, using a model building