“We wish to suggest a structure for the salt of deoxyribose
nucleic acid (D.N.A.). This structure has novel features
which are of considerable biological interest.”

So began a paper in Nature on April 25, 1953 perhaps becoming one of the greatest scientific understatements of all time.

“It follows that if the sequence of bases on one chain, is given, then the sequence on the other chain is automatically determined.”

“It has not escaped our notice that the specific pairing we have postulated immediately suggests a possible copying mechanism for the genetic material.

In terms of our 21st century way of describing things, Watson and Crick came up with a model which explains replication of the DNA in a ‘digital’ manner. Think of it this way, if you take a photocopy of a photocopy, something is lost in the process. If you were to take a photocopy of a photocopy of a photocopy over a period of time, it will turn out almost gray. This analogy is especially appreciated by science teachers who have been around long enough to experience trying to photocopy hand-outs over time. Now, we all have these worksheets in our computer, and each time we run off a new one, it comes from a digitized file. Each is as crisp as the previous. Likewise, each new strand of DNA is an becomes an exact copy of the previous. Of course there are exceptions to this, but the rate of error is less than of 1 in 10⁹. Thus, the Watson and Crick model for DNA made a quantum leap in the knowledge of science because it at once allowed us to describe both continuity and variation in living organisms in relatively simple terms.

In my previous blogs, I talked about the movie based on James Watson’s book. I also introduced some of the ‘giants’ providing the shoulders of knowledge to build the model on.

From my readings, I suspect that there were perhaps two major events leading to the thrust for solving the puzzle of life. First, there were a lot of scientists who had been working feverously in nuclear physics during the Second World War. When the war ended, many of the scientists wished to turn to something much more peaceful. Biological research seemed the perfect fit. The other factor was that there were still some poorly understood diseases devastating through the population. Watson, himself acknowledges partial funding from the National Foundation for Infantile Paralysis. (Founded in 1937 by Franklin D. Roosevelt, major fund raising came through the March of Dimes)

Erwin Schrodinger a much respected Nobel laureate had written a book called “WHAT IS LIFE?” in 1944. In it, Schrodinger questions “How can the events in space and time which take place within the spatial boundary of a living organism be accounted for by physics and chemistry?” This simple question spurred on countless physicists and chemist to apply their skills to newly developing field of Molecular Biology.

Watson, after hearing a talk by Maurice Wilkins on the X-ray diffraction of DNA, felt that the studies would lead to the unravelling of life’s molecule. Watson’s move to Cambridge and the intrigue surrounding the research is well documented in his book “The Double Helix” described by me in an earlier blog. Wilkins was using DNA provided by Chargaff, while Rosalind Franklin working at King’s college had an arguably purer sample provided by Rudolf Singer. Each of them were trying to interpret the patterns. Wilkins, a physicist and Franklin, a physical chemist, were poring over the data from their respective disciplines. James Watson with his background in biology, had teamed himself up with physicist Francis Crick , giving their partnership a much greater range of thinking about the problem. Definitely, when Watson described to Crick the patterns being produced by Franklin’s x-ray diffraction photographs, the possibility of a helical structure was strong in their minds. Additionally, they were aware of Chargaff’s work demonstrating what is now known as Chargaff’s Rules (A + G always equals C + T). And as mentioned before, they were aware of the transforming principles and the link to DNA.

Perhaps Watson and Crick were inspired by the Erwin Schrodinger’s statement “Indeed, the number of atoms in such a structure need not be very large to produce an almost unlimited number of possible arrangements. For illustration, think of the Morse code. The two different signs of dot and dash in well-ordered groups of not more than four allow thirty different specifications. Now, if you allowed yourself the use of a third sign, in addition to dot and dash, and used groups of not more than ten, you could form 88,572 different 'letters';” WHAT IS LIFE?,1944.


In the same issue of Nature which published the now famous Watson and Crick model, the paper by Wilkins, Stokes and Wilson helped verify the model with the publication in the same journal of the x-ray diffraction saying: “While the biological properties of deoxypentosenucleic acid suggest a molecular structure containing great complexity, X-ray diffraction studies described here show the basic molecular configuration has great simplicity.”

Roseland E. Franklin and R.G. Gosling wrote the third paper in the series. To me, it seems much more tentative in approach, yet full of data to back up their claims. “Thus our general ideas are not inconsistent with the model proposed by Watson and Crick in the preceding communication.” Yet her x-ray diffraction pictures are infinitely clearer than those published by Wilkins.

Scientists describe the universe through models. They look for a model which is simple, elegant and aesthetically pleasing. The model must also have the power to make predictions. The Watson and Crick model meets all this criteria. Within 50 years of the publication of the model, our knowledge of DNA has led all the way to the solving of the human genome project. It is ironic in a way that Francis Crick often described as the ultimate reductionist has had his model used as the starting point moving to the new science of genomics.