Science
Double helix
Bernard Dixon
Twenty years ago this weekend, two Cambridge scientists, Francis Crick and James Watson, were putting their finishing touches to the typescript of one of the most important scientific papers of all time. Published with appropriate speed in the scientific journal Nature on May 30, 1953, it was an account of the structure of DNA, the substance responsible for heredity in all animals and plants.
When a cell divides, and when an animal or plant reproduces, its genetic characteristics are passed on in the form of a code in the DNA molecule. By describing the shape of DNA, Crick and Watson solved, at a stroke, by far the greatest biological riddle of the day. They not only demolished formidable technical obstacles in revealing a highly complex structure, but showed how the molecule works.
DNA turned out to be a double helix — two long chains of chemical units, wound together round a cylindrical space. There were four different kinds of chemical unit but any one was always linked to the same partner in the other chain. It is the sequence of these units which determines hereditary characteristics, just as the dots and dashes of the morse code convey a message.
"It has not escaped our notice," Crick and Watson concluded their Nature paper, " that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material." Considering that biologists had been groping towards such an understanding for some twenty-five years, this must rank as one of the most preposterous throw-away lines ever published in a scientific paper. What the Cambridge duo were suggesting was that, given complementary pairing, either of the two strands of the DNA helix was sufficient to determine the assembly of its partner chain. This is precisely (it happens with great precision) what occurs when a cell divides. The DNA replicates by each of the two strands acquiring new complementary chains. Perfect copies of the original molecule thus pass into each of the two daughter cells.
As recounted in Watson's own account of this momentous discovery, in his book The Double Helix (Penguin), he and Crick were working under increasing pressure towards the end, anxious that no one else should scoop them in securing a uniquely prestigious scientific prize. The most serious threat was from Linus Pauling (a future Nobel prizewinner for his research on protein structure), then working away feverishly on the same problem at Pasadena. For one dreadful moment, the Cambridge group feared that Pauling had won the race, but then noticed that he had made an elementary error in his calculations. "The bloomer was too unbelievable to keep secret for more than a few minutes," Watson records. " I dashed over to Roy Markham's lab to spurt out the news and to receive further reassurance that Linus's chemistry was screwy." Later in the day, certain now that Pauling was wrong, Crick and Watson entered their favourite pub at opening time "to drink a toast to the Pauling failure."
Many of those who reviewed Watson's book when it was first published, expressed dismay that scientists should behave in this way. According to a popular caricature, scientists are supposed to be objective automata. Science is an activity that has no place for competitiveness, aggression, or envy. This is nonsense. Objec tivity is a tool of the trade, not a quality that should dominate a scientist's entire character and behaviour. And far from there being evidence that the competitive edge is harmful in science, there are many ex amples, like Crick and Watson, of scientists spurred on to more intense effort knowing that others were on the same track.
Besides, a study of history shows that scientists have become more civilised about these things, not less so. Isaac Newton, for example, had a corps of young mathematicians and astronomers working full time to secure his fame and register his priority in discoveries such as the calculus. A whisky at opening time seems a mild pleasure by comparison.
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