James D. Watson

James Dewey Watson (born April 6, 1928) is one of the discoverers of the structure of the DNA molecule. Born in Chicago, he has been fascinated by birds since he was a child due to the influence of his father. At the age of 12, he starred on the Quiz Kids, a popular radio show that challenged precocious youngsters to answer difficult questions. Thanks to the liberal policy of Robert Hutchins, he enrolled at the age of 15 at the University of Chicago. After reading Erwin Schrodinger's book What Is Life? in 1946, he changed his direction from ornithology to genetics. Watson earned a B.Sc. in Zoology in 1947.

The Structure of DNA

In October 1951, Watson started at the Cavendish Laboratory, the physics department of the University of Cambridge, where he met Francis Crick. Watson and Crick started an intense intellectual collaboration that in less than a year and a half resulted in their discovery of the structure of DNA. Crick soon solved the mathematical equations that govern helical diffraction theory and Watson knew all of the key DNA results of the Phage Group. In April 1952, Watson's PhD research advisor, Luria, was to speak at a meeting in England. However, Luria was not allowed to travel due to cold war hysteria over his marxist leanings. Watson used Luria's speaking slot to talk about his own work with radioactive DNA and the results of others in the Phage Group that indicated the genetic material of phages was DNA. It has been recorded that during this meeting Watson was passing on to others news from Wilkins about DNA such as the calculated width of the B-form molecule. By 1952 estimates from X-ray data and electron microscopy agreed that the diameter of DNA was about 2 nanometers.

Related Topics:
1951 - Cavendish Laboratory - University of Cambridge - Francis Crick

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

During 1952, Crick and Watson had been asked not to work on making molecular models of the structure of DNA. During 1952 Watson performed X-ray diffraction experiments on tobacco mosaic virus. Tobacco mosaic virus was the first virus to be identified (1886). Since electron microscopy revealed that virus crystals form inside infected plants, it made sense to isolate this virus for study by X-ray crystallography. Tobacco mosaic virus was the first virus to be purified (1935). Early X-ray diffraction images for tobacco mosaic virus had been collected befor World War II. In 1954 James Watson deduced from his X-ray diffraction images that the tobacco mosaic virus had a helical structure{{ref|TMV}}.

Related Topics:
Tobacco mosaic virus - Electron microscopy - X-ray crystallography

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Linus Pauling had made use of molecular models to solve the structure of the protein alpha helix. Could Watson and Crick similarly solve the structure of DNA; did Watson + Crick = Pauling? Not quite. Pauling had personally attained what was possibly the world's greatest understanding of chemistry. Neither Watson or Crick knew much chemistry. But Franklin was already within easy reach in London and the other source of the key chemical knowledge they needed would drop into their laps in 1952. Building on the X-ray diffraction research of Rosalind Franklin and Maurice Wilkins, they together deduced the double helix structure of DNA, which they published in the journal Nature on April 25, 1953{{ref|helix}}. Watson, Crick, and Wilkins were awarded the Nobel Prize in Physiology or Medicine for their discovery in 1962.

Related Topics:
X-ray - Rosalind Franklin - Maurice Wilkins - Double helix - Nature - 1953 - Nobel Prize in Physiology or Medicine - 1962

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Watson's key contribution was in discovering the nucleotide base pairs that are the key to the structure and function of DNA. This key discovery was made in the Pauling "tradition", by playing with molecular models of the four nucleobases. After realized that A:T and C:G pairs are structurally similar it was immediately clear that such structural pairing accounted for a key biochemical fact of DNA, the so-called Chargaff ratios, experimentally determined ratios of the amounts of the four nucleotide subunits of DNA: the amount of guanine is equal to cytosine and the amount of adenine is equal to thymine. Watson's exercise in molecular modeling was facilitated by Jerry Donohue who explained to Watson and Crick the correct structures of the four bases. This allowed Watson to visually line up the complementary base pairs that could be held together by hydrogen bonds.

Related Topics:
Nucleobase - Chargaff ratios - Guanine - Cytosine - Adenine - Thymine - Base pairs - Hydrogen bond

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The key contribution from Franklin was when she told Watson and Crick that the phosphate backbones of DNA should be on the outside of the molecule. When Watson and Crick finally accepted this fact, the bases had to go to the inside of the DNA structure where they would have to interact chemically. Watson discovered the nature of that interaction.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

Watson and Crick benefitted from two travel-related strokes of luck in 1952. Erwin Chargaff visited England in 1952 and rubbed Watson's and Crick's noses in the fact that they knew almost nothing about nucleotide biochemistry: they soon repaired their deficiency. And Linus Pauling did NOT visit England. His planned visit was cancelled for political reasons and he never gained access to the King's College X-ray diffraction data for DNA until it was published in 1953, along with the Watson-Crick model. It was also in 1952 that the final details of the chemical structure of the DNA backbone was determined by biochemists like Alexander Todd.

Related Topics:
Erwin Chargaff - Alexander Todd

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

In 1968 Watson wrote The Double Helix, one of the Modern Library's 100 best non-fiction books. The account is the sometimes painful story of not only the discovery of the structure of DNA, but the personalities, conflicts and controversy surrounding their work. Watson's original title was to have been "Honest Jim", in part to raise the question of the ethics of sneeking behind Franklin's back to gain access to her X-ray diffraction data before they were published. Watson seems to have never been particularly bothered by the way things turned out. If all that mattered was beating Pauling to the structure of DNA, then Franklin's cautious approach to analysis of the X-ray data was simply an obstacle that Watson needed to run around. Wilkins and others were there at the right time to help Watson and Crick do so. Also in 1968, Watson became the director of the CSHL (Cold Spring Harbor Laboratory) and made the CSHL his permanent residence in 1974.

Related Topics:
1968 - The Double Helix - Modern Library - Cold Spring Harbor Laboratory

~ ~ ~ ~ ~ ~ ~ ~ ~ ~

The Double Helix changed the way the public viewed scientists and the way they work. In the same way, Watson's first textbook, The Molecular Biology of the Gene set a new standard for textbooks, particularly through the use of concept heads - brief declarative subheadings. Its style has been emulated by almost all succeeding textbooks. His next great success was Molecular Biology of the Cell although here his role was more of coordinator of an outstanding group of scientist-writers. His third textbook was Recombinant DNA which used the ways in which genetic engineering has brought us so much new information about how organisms function. All the textbooks are still in print.

~ ~ ~ ~ ~ ~ ~ ~ ~ ~