A flexible and efficient storage system

In a short article in the scientific journal Nature, researchers Watson and Crick presented the structure of DNA and changed the course of the history of genetics

The second half of the 19th century brought with it the recognition that the phenomena of life can be understood through chemistry. One of the research groups that contributed to this was the one headed by Felix Hoppe-Zeiler in Germany. In 1869, at the University of Tübingen, his research assistant, the Swiss Friedrich Miescher, discovered a new and unknown substance produced from the nuclei of living cells. Until then it was accepted that living things were made of proteins only. Misher described the new material as "not suitable to belong to any of the known forms of protein", and gave it the name "nuclein", from the word nucleous - nucleus.

Misher won worldwide fame for this breakthrough - the discovery of DNA, the hereditary material from which chromosomes are made. But the detailed characterization of the new material was done by another researcher in the same laboratory, Albrecht Kosel, about ten years later. It was Kosel who discovered that the nucleic is built, among other things, from the four nitrogenous bases, known today as adenine (A), guanine (G), cytosine (C) and thymine
(T). For this, Kosel won the Nobel Prize for Medicine in 1910. Miescher's student, Richard Altman, later gave the new substance the name by which it is known today - nucleic acids, referring to the fact that its long chains contain phosphoric acid. Friedrich Miescher was very interested in the fertilization process. He produced the nucleic for the first time from pus taken from the bandages of wounded soldiers. Later he produced it from salmon sperm. In a surprising vision, Misher wrote in 1874 that "if any single substance might be the unique factor in the fertilization process, the first that comes to mind is the nucleic." 70 years passed until this hypothesis was proven beyond any doubt. The world wars were very damaging to German science, which until then had dominated the field of biological chemistry. The USA and England became scientific centers in the field. In 1944, Oswald Avery and his associates from the Rockefeller Institute in New York published a revolutionary article, in which they proved that the transfer of nucleic acids from one bacterial cell to another changes the hereditary properties of the receiving bacterium. In doing so, they contradicted the opinion that was accepted until then, according to which the genes are made of proteins. These researchers also failed to explain the chemical mechanism by which DNA controls the structure of the living cell and its properties. Even more important - it was not clarified how the genetic information is copied from generation to generation.

In the first decades after the discovery of DNA, scientists thought that it was an inert and boring substance, the same in its composition in all creatures. On the other hand, from the work of the Czech monk Gregor Mendel in the middle of the 19th century, it was known that there are some entities in living things - the genes - that allow each animal or plant to be different from another. How is it possible that the nucleic acids are the genes? Can the long chemical chains of DNA contain information?

The first hint was received when it became clear that different creatures have different DNA compositions, some are richer in the "letters" A and T and others in the letters C and G. Shortly after Ivory discovered the find, Erwin Chargaff, an American of Austrian origin, found an interesting and mysterious rule. In every DNA sample he tested, the amount of A was always equal to that of T, while the amount of C was the same as that of G. But how can these clues be put together into a complete picture with the help of which the role of nucleic acids as carriers of hereditary information will be explained? Four more years passed. In 1952, a young British scientist, Rosalind Franklin, devoted herself to experiments designed to clarify once and for all what the spatial structure of DNA is. Franklin did this at the University of Cambridge, together with Maurice Wilkins, using the method of X-ray crystallography, such as was applied by Kandro and Peretz at the same university to decipher the structure of hemoglobin. Franklin's results allowed her to conclude that DNA is a twisted coil. Also the key that the DNA bases face inward, to the heart of the coil, in such a way that they can react easily to each other, and only with great difficulty to external hostile entities.

At that time, two other scientists were working in Cambridge, the American James Watson, 24 years old, and the English Francis Crick, 37 years old, who were brilliant researchers, capable of perceiving and deciphering important problems in science. Watson and Crick spoke with Wilkins, and received Franklin's experimental data from him. Additional data from other laboratories were available to them. Equally important: Watson and Crick developed an excellent intuition regarding the exact structure of the building blocks that make up DNA. When they combined all of these into one piece, and not before guessing a few wrong structures, the two arrived, a year later, to decipher the structure of DNA. This achievement made the year 1953 symbolic of the most significant turning point in biology ever.

Their short article, published in the scientific journal Nature, is titled simply "Structure of DNA". It ends with a sentence that has become a byword: "We have not lost sight of the fact that the specific pairing of bases in the described structure makes it possible to propose a copying mechanism for the genetic material." Thus, in a wonderful example of understatement and brevity, Watson and Crick changed the course of the history of genetics.

What was hinted at in the article became the solid foundation of molecular genetics. The structure of the double helix of DNA allows any sequence of bases to be included in it without spoiling the line. In this way, a flexible and efficient storage system is obtained for data that translates into instructions for building proteins and controls the details of the structure of each living cell. DNA contains the genetic information twice - a kind of image and its negative. According to the structure of Watson and Crick, opposite the base A is always placed in the opposite strand the base T, and opposite G is placed C, and vice versa. The excellent insight of the pair of scientists allowed them to accurately characterize the chemical forces (called hydrogen bonds) that govern this unique match. At the same time, their findings made it possible to explain Chargaff's mysterious quantity relations, and even the need for the bases to turn inwards, towards each other, as Franklin had predicted.
The hypothesis hinted at in the last sentence of the article is that if the strands are separated, each of them will be able to grow a new opposing strand according to the matching laws, and thus the original coil will be duplicated. This is the molecular basis of gene copying. For their discovery, Watson and Crick received the Nobel Prize for Medicine and Physiology in 1962, which they shared with Wilkins. Rosalind Franklin's failure to share in the glory - both due to her being a woman at a chauvinist-male oriented university and also due to her death from cancer before the prize was awarded -
Considered by many to be a terrible injustice.

Next year the whole world will mark the full anniversary of the genetic revolution of 1953. It is hoped that in 2003 the reading of the last details of the DNA sequence of the human genome will be completed. It will be a symbolic moment of the victory of human reason and the closing of the circle, which opened with the discovery of DNA.