If deoxyribonucleic acid sounds unfamiliar to you, then you will surely recognize it in its short form, DNA. One of the greatest breakthroughs in the last century was the discovery of the DNA. Its discovery has paved the way for the development of a number of genetically engineered drugs, hormones and other useful substances. Scientists now hope to access to a complete map of the human genetic code, which in turn would help trace the genetic causes of inherited disorders or congenital diseases and probably lead them to prevention and cures too. Besides medical professionals, the discovery of the DNA is helping the lawmakers and protectors too.

The DNA was first isolated by a Swiss physician, Friedrich Miescher, in the year 1869. However, its functions remained unknown. Gradually, it was learnt that the DNA contained phosphate, a sugar called deoxyribose and four different compounds called nucleotide bases. It was only in the year 1944 that a Canadian-born bacteriologist, Oswald T. Avery and his colleagues proved, through a series of experiments, that DNA transmitted genetic information. Prior to this, it was believed that proteins were the source of genetic information.

Through the good offices of a Swiss physicist, Wilkins received a uniquely pure sample of DNA in the year 1950. From this sample, he succeeded in identifying single DNA fibers. Wilkins and Gosling X-rayed these fibers. In 1951, Rosalind Franklin, an expert in X-ray crystallography (a technique that can create images of the structural relationships between atoms and molecules of chemical substances), joined the duo and she too X-rayed the fibers. However, soon Wilkins and Franklin fell out and Franklin was asked to leave the team. When she left, she was asked to submit her photographs of the images produced by the X-ray crystallography, which are also called diffraction photographs. One of these photographs showed that the DNA molecule had the shape of a double helix, a structure resembling a twisted ladder.

Diagrammatic representation of a  double helix structure of a DNA molecule, resembling a twisted ladder

In the meantime, the team working at the Cavendish Laboratory struck luck in the form of an American biologist, James Watson, who chanced to see one of the diffraction photographs. Also concluding that the structure of the DNA may be a double helix, Watson joined the Cambridge team in the fall of 1951. He managed to convince a team member, a British biophysicist, Francis Crick, that a combination of model building—using plastic balls, wires and steel plates—and X-ray crystallography could lead them to the structure of DNA.

Francis Crick

There was more to the DNA than its helical structure that needed to be explained. Its chemistry, for instance. Watson began working on the increasingly complex model of the molecule. It was in early 1953 that he could claim to have completed his work. This model incorporated all the known chemical components of DNA and closely matched the diffraction pattern observed in Wilkin’s photograph. Watson and Crick had accurately deduced that “the two strands of the double helix separated before cellular division, providing templates, or patterns, for the creation of two new DNA molecules identical to the original.”

The discovery gained recognition when a leading science journal published three articles, one article from the Cambridge team and two from King’s College in London, on the molecular structure of DNA. Wilkins, Watson and Crick shared the Nobel Prize for physiology or medicine, in the year 1962.

James Watson