Propeller that would change the world
The discovery of DNA structure rests on a few basic elements that provided each part of the knowledge necessary to understand, finally, it was made the molecule of life.
We know, for some time, thanks to the studies of chemistry that comes deoxyribose in DNA composition, some groups like phosphate and nitrogenous bases: thymine, adenine, cytosine and guanine. It also found that there is a certain relationship of proportionality between the quantities of these bases: the amount of cytosine is equal to that of guanine and the thymine – with the adenine. (Chemist Erwin Chargaff discovered that, as the phenomenon is called Chargaff’s rules.) What could this mean still not known.
Another key element was the work of Maurice Wilkins and Rosalind Franklin, who studied for years in X-ray crystallography applied various molecular structures and X-ray diffraction images of DNA by them led to the idea that could be talking about a helical structure.
The idea of a helical structure of complex molecules floating in the air at the time; very short time ago, a famous American chemist Linus Pauling, who worked at the University of California (Cal Tech) discovered that many proteins have such a structure, called alpha-helix, which had led to the assumption that other complex molecules could have such a configuration.
This was the state of knowledge about when Fracis Crick and James Watson have decided to grasp to study the structure of DNA.
Today, studies on the structure of molecules are using computer programs, complex, three-dimensional molecules that effectively draws, then twist and twist them in all positions, helping enormously to understanding their configuration. In the 50s, but there was nothing like this. New, used computers participation in scientific research, it’s hard to believe that Watson and Crick discovered the structure of DNA three-dimensional models of manual assembling wires and metal plates representing phosphate groups, deoxirboza, nitrogenous bases and the connections between them. The plates and the wire was cut at the level so as to correspond to the particular size of the groups of atoms and chemical bonds and hydrogen length of the DNA strands as they were derived from the data of chemical and X-ray diffraction images Monday days, Watson and Crick were all such models built by putting pads in certain angles, measuring out distances, for everything to fit together. And before success, there were many disappointments.
Today, when we made DNA is seems simple, of course, but remember that when nobody knew how the molecule looks complicated. It is suspected that the shape of a helix, but many strands consisted not known from the beginning.
At one point in 1951, the famous Linus Pauling at Cal Tech (Cavendish Laboratory institution which was in competition, each team of scientists hoping to discover the structure of DNA and the first to receive the Nobel Prize for success), published a paper in stating that discovered the mystery: DNA has a helical structure, consisting of three strands. There was an error difficult to explain to a scholar of his stature – he was the greatest specialist in structural chemistry of the era and one of the greatest of all time – and yet he did. (Proof that anyone can make mistakes, especially when rushing for fear of taking others before him.)
Crick and Watson and realized that something was wrong and relying on X-ray diffraction photographs by Rosalind Franklin and Raymond Gosling her assistant (especially a certain image, called “picture 51”, which took an important role in success), they hypothesized that it would be rather of a helix consisting of two strands. It is not yet known how these chains are stacked to form the propeller. It has long been believed that the phosphate groups and deoxyribose string is in the middle of the helix – like a spine – and nitrogenous bases side out, but three-dimensional models built on this assumption not arrange properly. Distances and angles corresponding to molecular and chemical bonds does not lead to a correct combination plates.
Finally, the assumption was made for the opposite: the side apart, they would find rows of deoxyribose-phosphate group, and in the center, nitrogenous bases which are joined to each other (in a more understandable). It is the merit of Rosalind Franklin to insist on this point, convincing them eventually and Crick and Watson that model as the foundation to the center right.
But as linked to each other these nitrogenous bases to stabilize the spiral staircase?
Initially, Watson and Crick thought the bases bind similar principle similar – ie adenine with adenine, thymine with thymine etc. But again their metal models goes wrong, and talking to a few chemists who helped to check the calculations, Crick and Watson concluded that the foundations were mingled by another rule, that of complementarity, which satisfy Chargaff’s rules: adenine always bind thymine and cytosine – guanine. This model had the advantage explain plausibly how DNA replicates – in what way, ie, was it copied before cell division so that the unit cell daughter receive identical copies of DNA cell-mothers.
And finally, after many roads and calculations after disputes with fellow scholars and bitter disappointment when things proved wrong, after countless attempts to build three-dimensional models of metal so that it easy to combine, natural and flawless came the day – February 28, 1953, as indicated by a plaque placed on the wall “Eagle” – when Crick and Watson have entered the premises in question, and Crick, which Watson describes in his book as an extreme type of talkative and with a loud laugh, cried, loudly, that they discovered the secret of life two!