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a three - manBy LYW DALGARNODNA —THE DOUBLE HEI IX. James D. Watson. WeiiUn* fell and \icohon. 226/*/» Price S4-90.IN 1953 a brief article in ‘Nature’, theBritish scientific periodical, provided the key to what Sir PeterMedawar called “themost important complex of scientific discoveries of the 20thCentury’*.The note proposed an elegantly simple structure lor the fundamental hereditary material DNA (deoxyribosc nucleic acid) and was altogether too pretty not to he true. the authors, Drs James D. Watson and Francis Crick, were subsequently awarded a joint Nohel Prize with Dr Maurice Wilkins in recognition of their achievement. Dr Wn' son’s book provides a youthful, fascinating and highly personal account of the events which led these three scientists from relative obscurity to celebrity in two yean.In 1950 Watson, a Ph D. graduate in biology from Illinois. left the USA for further research in Copenhagen. He was already set on his scientific aim: to understand the chemical nature of the “gene”, the hereditary unit about which so little was known. Watson (and many others) believed that geneswere made of DNA. and that ‘information’ was stored in this fundamentally simple molecule. But how could a long thread-like molecule, composed only of permutations of four different units (the ‘bases’) hold, say, 20,00(1 bits of information? And how was this information copied accurately and distributed when a cell reproduced?Copenhagen was not particularly useful in answering these questions, and Watson moved to England where he was given a room with Francis Crick, a brilliant garrulous 35-year-old ex physicist toiling to finish his Ph DWatson's intense preoccupation with DNA was soon to divert Crick from his own studies on proteins. To Watson it was clear that the structure of DNA was “up forErabs*', and that if they didn’t urry. the groat Linus Pauling at Cal Tech would get there first Pauling had just “scooped” (a word often used by Watson) the Cavendish Laboratories in their own field, the structure of proteins, lie was now free to repcut the process with DNA.Pauling’s success with protein structure was to be of great significance to the DNA studies; he had shown that the regular spacing of units (amino acids) in the protein molecule gives it a helical ('stretched spring') shape.This reasoning could apply to DNA as well; the units in DNA were the four fiat ‘bases’ (adenine, thymine, guanine and cytosine). But did Wilkins' X-ray resuits support such a structure?Crick, a crystallogrnpher, was well qualified to interpret the data which the enthusiastic Watson brought back from his visits to Wilkins in London. It seemed that DNA could be a helix, although it was not clcur whether the helix was made oi two, three or four intertwined strands. Watson, taking a leal out of Pauling's book, started building accurate molecular models of possible shapes but no obviously correct structure emerged. The problem rested for a while; Crick went hack to his proteins while Watson pondered Frwin ChargafTs curious results on the composition of DNA These showed that the number of adenine and thvminc molecules was always equal; similarly guanine always equalled cytosine. If seemed a key observation, hut how did it fit info a general structure for DNA?The next step in solving the DNA riddle was Watson’s major contribution (apart from his directed persistence, he mainly generated creative excitement in Crick). Watson’s feeling that “important biological objects come in pairs was singularly applicable to‘scoop’DNA. With ChargafTs data in mind. Watson tried to link cardboard models of the bases together in a specific way. Miraculously he found that adenine only links to thymine, and guanine pairs only with cytosine The problem was falling apart. If one base was always paired with another, bases in one strand of DN A could uniquely specify ‘complementary’ bases in another strand More X-ray data from Wilkins laboratory arrived. These were consistent with a double-stranded molecule A fium of model building hy Watson and Crick and the structure was out DNA was a double helixWatson’s early fear that the structure would be dull was unfounded Its simple symmetrical beauty delighted scientists; they were relieved that there was nothing chemically abstruse or mystical about the genetic material. The DNA molecule was held together hy thoroughly understood conventional chemical forces. The model immediately suggested that when cells divide und pass on their genetic information, the DNA helix unwinds like a two-stranded rope.The book illuminates the way in which certain rare types of scientific discovery arc made . It also emphasises the dependence of »ncb discoveries on a pre-existing body of experimental data, patiently collected by other workers.
Newspaper Details
Canberra Times
Canberra, Australian Capital Territory, AU
Sat, Aug 03, 1968
Page 7
Full Page
Clipped by
Grandmere E.
OR, USA 05 Jun 2022
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