24 Nov 2016
Biophysicist Dr. Doping speaks about X-ray analysis, bases and forms of DNA. Who has played an important role in determining the structure of DNA along with Francis Crick and James Watson? Why DNA molecules initially investigated by X-ray? As identified pairs of complementary DNA?
DNA as the molecule in the nucleus of living cells, was discovered a long time ago, back in the 60s of XIX century. This discovery made the Swiss physician Miescher. But the real history of DNA began with the opening of its molecular structure, which occurred much later in 1953. Since DNA is becoming more and more well-known because of their central role in vivo.
How and by whom was discovered DNA? Everyone knows that the DNA was discovered by two scientists: Englishman Francis Crick and James Watson, an American. The opening took place in the United Kingdom, Cambridge. There Watson was on probation. Then he was a young biologist, he was 24 years old, and he came to Cambridge, the Cavendish Laboratory, because I was already quite keen on the idea of determining the structure of the DNA molecule. By this time it has accumulated data which for him were convincing, although not all were convincing that DNA is the carrier of genetic information. And there, at the Cavendish Laboratory, he met Crick, with whom they quickly became friends - exactly because Crick was exactly the same fad, he, too, was quite obsessed with the idea that the gene is the secret can be revealed by determining the structure of the DNA molecule.
Vitamin B12 Cyanocobalamin injection - is essential for making DNA.
But they did not have any opportunities to carry out experiments. Experiments with DNA made in another laboratory, also in the UK, in London, at the Royal College, and these experiments were conducted Rosalind Franklin, an expert in X-ray diffraction analysis, - she has played a key role in the further drama that unfolded on the definition of the structure of DNA, as well as, Of course, with Watson and Crick.
Rosalind was working on DNA, its structure, and although it was not the first one who tried to take pictures of X-ray scattering from the DNA, she was able to make the crucial step in the right direction. The fact that X-ray analysis is usually necessary to obtain crystals molecules. In very long DNA molecules that do not crystallize. Therefore, instead of crystals Rosalind studied the DNA fibers. That is, the DNA dried, it was not dissolved, such as jelly, from which stretched molecules in one direction, and they are lined up more or less in one direction. Then they directed beam of X-rays, studied the picture of the scattering of light.
She was faced with a very serious difficulty: the photos that were obtained at the same time, were very poorly reproducible and completely unintelligible.
And here she made this outstanding step. She thought that perhaps there is there is a mixture of structures, this ratio structures is poorly controlled, and can be, depending on the humidity of the sample. She took the camera, which maintain a fixed humidity, and began to change the humidity. Indeed, she found that when high humidity is one of the scattering pattern at a low humidity very different picture of the scattering. And the fact that she had watched before, it was an uncontrolled mixture of the two. She realized that there are two different forms of the DNA molecule, and she called a form of low humidity A-shape and form at high humidity B-form. Of course, B-form is of greatest interest, because the DNA in the cell is at high humidity, in water.
The most important event in this drama was that Watson and Crick became known that X-ray, this scattering pattern. In fact, Rosalind wanted to determine the structure of DNA itself, and she did not want anyone to interfere in this process. But she did not get around to it, to figure out how to be in this radiograph. It is something already realized important things she knew, looking at the X-ray. But the structure is not built. But Watson and Crick learned of this picture. They learned it is not entirely ethical way, because Rosalind did not want to see someone is seen and interpreted. They managed to get the picture, and they immediately understood the basic parameters of the structure of DNA.
Then we have become a model to build on the basis of these parameters, which are derived from Rosalind Franklin experiment. And, of course, it is absolutely the most important step was when Watson - as he describes a very dramatic in his famous book "The Double Helix", where he presents his version of events, - began to try to make a pair of four bases, which are part of the DNA. He already knew that it was two lines, it is a double helix, was trying to make a couple of them, and that he eventually succeeded, it is now well-known complementary pairs A - T and the G - C. And when he did, then they turned out great beautiful model of B-form DNA, which is the famous double helix, it is the very structure of which genetic information is stored in all the cells of all living organisms on Earth.
This was done, probably the most remarkable discovery, at least in the field of biology and medicine, the most remarkable discovery in the history of science, perhaps, the most remarkable discovery in the history of science in general. It is surprising that this article was published and very quickly took exactly one page of the journal Nature. This is a very short article. Grand opening does not require a lengthy explanation.
With this publication, which was carried out April 25, 1953, begins the countdown of a new era in the history of human civilization, the DNA era, when we know that all living organisms are constructed in accordance with the instructions laid down in the DNA molecule, in parts of the sequence of four letters: A , T, G and C, - in the DNA sequence and the DNA double helix is 2 nanometers in diameter, a very long - depending on the number of links in the chain.
If the DNA taken from a human cell and extend in one line, it will turn a small molecule thickness and a length of about 2 meters. Now all our knowledge, all our understanding and biology, and medicine is based on the fact that we know the structure of DNA, and we know that DNA is the carrier of genetic information. This knowledge gives us the opportunity to intervene in an unusually efficient processes, phenomena of life at all levels and in microorganisms and higher organisms, and in man.
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