school energy&environment

The scientists and the stages

Why does the discovery of 1953 become a milestone in understanding the genetics of life and the evolution of Man and other living creatures?  To understand the importance of the double helix of DNA it is interesting to retrace the main stages of the studies on DNA that were done before and after the publication of the first article by J. Watson and F. Crick on Nature. The first information regarding the existence of DNA goes back to 1869, F. Miescher mentions an acid substance that he calls nuclein that is contained in the nucleus of cells and is composed of protein and nucleic acid – this will subsequently be called DNA. From then on many studies are carried out on the subject.  In 1938 the scientists R. Signor, T. Caspersson e E. Hammarsten understand that the DNA molecule is formed by long chains (sequences) of nucleotide bases. The nucleotide bases (or nucleotides) are, as we have already seen, 4 different building blocks that make up the long acid molecule of DNA and are called: adenine, thymine, guanine and cytosine. In 1944, other university researchers suggest for the first time that the DNA molecule contains genetic information.  The genetic information (the set of instructions that cells need to build proteins) is assumed to be encoded in the different sequences of nucleotide bases that are repeated on the DNA chain.
Subsequently it is understood that it is in the DNA, that is transmitted from one generation to the next, from parents to children, that you find the genetic information that every cell of our body needs to carry out its specific function. Finally in 1952, A. Hershey e M. Chase establish that only the DNA molecules can be genetically transmitted to the next generation and not the proteins. In the very same year the scientist R. Franklin together with her colleague R. Gosling (a friend of J. Watson and F. Crick) produce a very well defined and clear map of X-ray diffraction obtained by bombardment of the DNA molecule. In fact, this is the famous photograph that inspired the intuition of 1953 on the three-dimensional nature of DNA.
In 1958 there is a breakthrough, M. Meselson and F. Stahl understand and illustrate the mechanism by which DNA reproduces: the double helix unwinds, it opens and two long parallel chains are obtained. Each filament is copied and in this way two identical copies of the original DNA molecule, that does not exist anymore, are obtained. It is only at this point really that the discovery of 1953, regarding the three dimensional structure of DNA, becomes very important because the exact knowledge of how the molecule is made in its three dimensions helps the understanding of its reproduction (with the mechanism explained earlier regarding the separation of the two chains) resulting in the formation of other double helixes that wind up and are identical to the original. At this point researches continue feverishly; in 1959 it is discovered that the filaments are copied and duplicated by an enzyme present in the cells of our body called DNA polymerase. Now the mechanism of genetic transmission is clearer and in 1961 the fact that specific molecules of DNA can conduct and instruct the construction, i.e. the synthesis, of specific proteins is understood.
Even though now it is clear that all these important discoveries are the outcome of the work of many researchers, the merit must certainly not be taken from those who had the first fundamental intuitions on the long path of learning that goes on even today. In fact, in 1962, James Watson, Francis Crick and Maurice Wilkins receive the Nobel Prize for their discoveries regarding DNA.