DNA Discovered

DNA Discovered

In February 1953, a zoologist from Indiana and a physicist from Northampton, England, walked into the Eagle Pub in Cambridge for lunch and “had to pinch ourselves.” James Watson (the American) and Francis Crick had just built a three-dimensional model that they thought might solve the puzzle of the structure of DNA, Deoxyribose Nucleic Acid. “When we went to lunch, we realized it [the model] was probably true because it was so pretty,” Watson later recalled. He says that Crick then turned to him and said, “We have found the secret of life!”

Indeed they had, and now – roughly 50 years later – their discovery is changing agriculture.

Other scientists, beginning with Gregor Mendel, had figured out how genes were passed down from generation to generation. Crop scientists and livestock breeders had systematically used that knowledge to select for desirable traits in hybrid crops and animal species. Other scientists had suggested that DNA was the molecule that carried genetic information, and that DNA was made up of phosphates, sugars and four bases. They even knew that the bases seemed to be paired – in any specific DNA molecule, there was always the same amount of Adenine as there was Thymine and the same amount of Cytosine as there was Guanine. But no one had worked out the structure. That structure would suggest how the molecule reproduced itself and how it might control the genetic traits so important to agriculture.

A few other scientists – including Linus Pauling at Cal Tech and Rosalind Franklin at Kings College in London – had been focusing a very narrow beam of X-rays onto a DNA molecule. When the beam hit the atoms in the molecule it was diffracted and the resulting pattern was recorded on a sheet of film. Pauling had suggested a structure for DNA, but his model wouldn’t hold together chemically.

Rosalind Franklin had produced scores of diffraction patterns and Watson had even heard her lecture on some of them. But she didn’t realize what she had, yet. Watson did.

Somehow, he and Crick were given a copy of one of Franklin’s images that became known as “Photo 51.” It showed a pattern of 16 dark globs in an X pattern. Watson and Crick immediately knew that the X indicated that the structure was a double helix with the bases on the inside. Mathematically, they had worked out what the diffraction pattern of a double helix would look like. Franklin’s photo fit their pattern. In addition, they could figure out the distances involved between different molecules in the DNA structure. From that information, they built the model that was “too pretty” not to be true.

From February 28, 1953, when they finished the model it was less than a month until they published a short article in the journal Nature on April 25. The paper has been called “biology’s biggest moment in the 20^th century.”

But no one noticed.

Three weeks later, on May 15, the News Chronicle of London ran an article about the discovery. The next day, the New York Times ran an article in its early editions headlined “Form of ‘Life Unit’ in Cell is Scanned.” But the article was considered so unimportant that it was replaced by ‘more important’ news in later editions.

Gradually, other scientists and then the media and the general public began to realize how important the discovery was. Later research by Watson, Crick and others figured out how the DNA molecule unwound and reproduced itself. Scientists figured out how specific genes and sequences of DNA would be used by RNA to build sequences of amino acids. Other research suggested that amino acids produced the proteins that translated into specific genetic traits. When these processes were understood plant and animal breeders began to dream of a day when they could modify specific genes and control specific desirable traits to produce better yields, better resistance to insects and disease and even the production of specific proteins or compounds in the organism.

As agronomy professor Alex Martin notes, the discovery of DNA produced a revolution in agriculture, but it was a deliberate one. “It didn’t revolutionize it two years afterward,” Alex says. “We had a new tool, but we didn’t know what we could do with it… Molecular biology was really invented since I went to school. And so, much of the public is not particularly familiar with it. And you tend to distrust or be nervous about something you don’t understand.”

The era of genetic engineering that has produced new genetically modified food organisms began with Watson and Crick’s model of DNA in 1953.

The PBS science program NOVA has a wonderful set of slides that help people visualize DNA and the way it works here.

Written by Bill Ganzel, the Ganzel Group. First published in 2007. A partial bibliography of sources is here.