[The discovery of DNA]

[The discovery of DNA]

Since the Mendelian genetic law was rediscovered after, it has raised a question: genetic factor is not a material entity? In order to address the question of what genes are, people are starting to nucleic acid and protein research.

As early as 1868, people had discovered the DNA. German chemist in the laboratory Hepei Le, a graduate Mingjiaomixieer Swiss (1844 - 1895), his laboratory near a hospital threw a bandage with a flu Nongxue interested, because he knows that in order to defend those Nongxie human health and disease " 'operations," and died in the WBC and the human cells were killed "remains." So he carefully bandage on the Nongxue collection, and using pepsin to break it down, found the bodies of most of the cell decomposition, but the nuclear non-functional. He further analysis of nucleus material found in the nucleus containing a phosphorus and nitrogen-rich material. Hepei Le experiments with yeast, that the nucleus of Michel substances found to be correct. So he would give such nuclei isolated from the material named "radionuclide", but found it was acidic and therefore diverted called "nucleic acids." Since then people have carried out a series of effective nucleic acid research.

In the early 20th century, Germany Kesaier (1853 - 1927) and two of his students Jones (1865 - 1935) and in the text (1869 - 1940) study, made clear the basic chemical structure of DNA, that it Nucleotide is composed of many macromolecules. By the nucleotide bases, consisting of phosphate and ribose. There are four kinds of bases (adeno-Piao Yin, the birds purine, thymine and cytosine), there are two ribose (ribosomes, deoxyribose), the nucleic acid into ribonucleic acid (RNA) and deoxyribonucleic acid ( DNA).

In a hurry to the text of his research results, erroneously think that the four kinds of bases in DNA is in the amount equal to nucleic acids derived from the basic structure of four nucleotide bases with different connections into the four nucleosides Acid as a basis for a nucleic acid polymer, proposed a "four nucleotide hypothesis." This hypothesis wrong, the understanding of the complexity of DNA structure considerable impediment, to a certain extent, affected the people's understanding of the function of nucleic acids. It was felt that although the nucleic acid present in the structure of the important - the nucleus, but its structure is too simple, it is difficult to envisage it in the genetic processes in what role.

Protein than the discovery of DNA as early as 30, have developed rapidly. The beginning of the 20th century, composed of 20 kinds of amino acid protein of 12 species have been found, in 1940, all were found.

1902, a German chemist for Xieerchi between amino acid peptide chain connected to the formation of protein theory, in 1917 he was synthesized from 15 glycine and three leucine composed of 18 long-chain peptide . Therefore, the idea of some scientists is possible that the genetic proteins play a major role. If the nucleic acid involved in genetic role, but also must be linked with the protein in the NP role. Therefore, when biological protein is generally inclined to think that the carrier of genetic information.

1928, the United States scientists Griffith (1877 - 1941) in an Clostridium perfringens, and a toxic-free capsule, toxicity weak Streptococcus pneumoniae experiments on rats. He has pod after killing bacteria with high temperature and no pods with live bacteria injected into mice, and he soon found that mice were killed, while the blood from his rat isolated from the live bacteria have dioxin. This shows that even without pods of dioxins from the dead bacteria have obtained material so that no dioxin into a pod of bacteria. This assumption is correct? Griffith also done experiments in the test tube and found that the death of the US with live bacteria without passing on the tube train at the same time, without all of pods into a pod bacteria, and found that the length of a pod proteins dioxin is a pod of dead carcasses left in nucleic acids (as in the heating of dioxin in the nucleic acid has not been damaged). Griffith said the DNA "conversion factor."

1944, the United States Xijunhuajiaaifuli (1877 - 1955) from the US bacteria isolated from the activity of "conversion factor", and this kind of material to the existence of the protein test pilot, the results are negative, and that "conversion factor" is the DNA. However, this discovery has not been widely recognized, then the technical people can not be suspected in addition to net protein, a protein residues into effect.

American scientists Delbrück Germany (1906 - 1981) phage group Aifuli firmly believe in the discovery. Because they are under electron microscopy to the form and enter the phage the growth of E. coli. Bacterial cells phage is a virus host, and individual small, only by electron microscope to see it. It is like a small tadpole, the external component is the first membrane protein and a tail sheath, the first internal contain DNA, on the tail end of silk sheath, the substrate and small hooks. When the phage infection E. coli, the first cherish in the tail end of the bacterial cell membrane, and then it all in the DNA injected into bacteria cells to the protein shell remain in the bacterial cell outside, then did not play a role in what . Bacterial cells enter the phage DNA, on the use of bacterial phage material rapid synthesis of DNA and proteins, which many copy with the original phage exactly the same size, shape new phage until the bacteria are completely disintegrated, leaving only these phage dead bacteria, go other bacterial infection.

In 1952, key members of phage group Hershey (1908) and his students Chase isotope labeled with advanced technologies in phage infection E. coli experiments. He E. coli T2 phage DNA marker 32 on the P protein shell markings on the 35 S. Marking the first use of T2 phage infection E. coli, and then be separated from the results of phage 35 S will be marked with shell stay outside in E. coli, only with the internal 32 P phage DNA markers all Notes Escherichia coli, E. coli, and the successful conduct of phage reproduction. This experiment proved that DNA is the genetic information transfer function, and proteins from the instructions of the DNA. This result immediately accepted by the academic community.

Almost at the same time, Austria biochemists investigation Mrs. (1905 -) on the four kinds of nucleic acid bases in the content of the re-determination has been fruitful. Aifuli in the impact of the work, he opined that if different kinds of DNA is due to the different, the structure of DNA must be very complicated, otherwise it is difficult to adapt to biological diversity. Therefore, he set out on the text of the "four nucleotide hypothesis" had suspected. In 1948 - 1952 the four-year period, he used more than in the era of precision paper chromatography separation four kinds of bases, UV absorption spectra to do quantitative analysis, after many repeated experiments, they finally come to a different out text results. The experimental results show that, in the DNA macromolecules in the purine and pyrimidine equal to the total number of elements, including adenovirus purine A and the same number of T thymine, birds purine G equal to the number of C and cytosine. DNA molecules in the base of A and T, G and C pair exist, thus negating the "four nucleotide hypothesis", as well as exploring molecular structure of DNA provides an important clue and a basis.

April 25, 1953, Britain's "Nature" magazine published in the Watson of the United States and the United Kingdom Kerik cooperation of the University of Cambridge in the United Kingdom research results: the double helix structure of DNA molecular model, which was later known as the results 20 Biological aspects of the past century's greatest discoveries, marking the birth of molecular biology.

Watson (1928) in the secondary school age is an extremely intelligent child, 15-year-old when they entered the University of Chicago study. At that time, due to an earlier permit experimental studies of sex education programme to Watson the opportunity to pursue all aspects of the integrity of the biological sciences courses. At the university, although Watson in genetics little formal training, but since reading Schrodinger settlement "What is Life? -- The physical appearance of living cells, "which led him to" find genetic secrets. " He was good at brainstorming and gaining public long, good at using other people's ideas to enrich themselves. As long as the conditions to facilitate access, not force yourself to learn a whole new area, can also be required knowledge. 22-year-old Watson, and received a doctorate, and then was sent to Europe to study postdoctoral fellows. In order to fully understand a gene's chemical structure of the virus, he went to study chemical laboratories in Copenhagen, Denmark. Once he went to Naples, Italy, mentors participate in a meeting of biological macromolecules, and the United Kingdom have the opportunity to listen to the physical biologists Wilkins (1916 -)'s speech, Wilkins saw the DNAX-ray diffraction photos. Since then, the search for the key to solve the structure of DNA in the idea in the minds of Watson recovered. Where can I study of X-ray diffraction pattern? So he went to the University of Cambridge Cavendish Laboratory study, in the meantime Watson understanding Kerik.

Kerik (1916) on the passion of science and secondary schools, graduated from the University of London in 1937. In 1946, he read the "What is Life? -- The physical appearance of living cells, "a book for the knowledge of physics to biology to the study of biology from an interest. In 1947 he began graduate to the study, in 1949 he Peiluci together with the use of X-ray technology research protein molecular structure, and Watson was in a meeting. Kerik time than the 12-year-old Watson, the lack of a doctorate. But they talked very speculative, Watson was here even know how to find a DNA protein is more important than the people who really Sanshengweinie. Watson at the same time he was in contact with the people, Kerik is the most intelligent one. They talk at least a few hours every day to discuss academic issues. Two complementary and mutual criticism and stimulate each other's inspiration. They believe that the molecular structure of DNA resolved to open the mystery of the genetic key. Only through the use of precision X-ray diffraction data can be more quickly identify the structure of DNA. In order to be made into DNAX-ray diffraction data, Crick invited Wilkins to Cambridge for the weekend. In conversation Wilkins accepted the spiral structure of DNA is the view also talked about his collaborators Franklin (1920 - 1958, female) as well as laboratory scientists, but also hard thinking model of the structure of DNA problems. From November 1951 to April 1953 18 months, Watson, Crick and Wilkins, Franklin and had several important academic exchanges.

In November 1951, after listening to Franklin Watson on the structure of DNA more detailed report, inspired by a certain knowledge of the crystal structure of Watson and Crick realized that in order to quickly establish DNA structure model only others use the analysis of data. They soon put forward a three helix structure of DNA envisaged. By the end of 1951, they invited Wilkins and Franklin to discuss this model, Franklin pointed out that the DNA in their calculations half less water content, so the establishment of the first model ended in failure.

One day, Watson and Wilkins to the laboratory at King's College, Franklin Wilkins recent shoot out a system of "B" DNA X-ray diffraction photos. Watson see photo, immediately excited, and also speed up the heartbeat, because this image than in the past been "A" much simpler, as long as a little look at the "B" of the X-ray diffraction photos, then by simple calculation, DNA molecules can be identified with more than the number of nucleotide chains.

Please help mathematicians Kerik, the results showed that the source of Yin attractive pyrimidine trend. According to the results of their investigations from Colombo and got the DNA of the two purine and pyrimidine 2 February 2 equal results, and formed a base pairing concept.

They hard to think of the four kinds of bases order, again and again in the base structure-paper painting, playing with model assumptions made time and time again, and again, to overthrow their own assumptions.

On one occasion, Watson also playing with the idea on its own model, he shifted base to remove the possibility of looking for a variety of matching. All of a sudden, he found that two hydrogen bonds connect the gland fat-yin, and even for a thymidine by three hydrogen bonds linking the birds allopurinol Ridge on a cytosine have the same shape, it was the spirit of his colleagues. Because of the number of purine and pyrimidine why the number was identical to this mystery solved. Mrs. investigation of all of a sudden it became DNA double helix structure of the inevitable result. Therefore, how a chain as a separate template synthesis of the complementary base sequence is not hard to imagine the chain. Well, two of the skeleton chain must be in the opposite direction.

After Watson and Crick continuous tension, quickly completed DNA metal model assembly. From this model that linked DNA from two nucleotide composition, along the central axis them to the opposite direction entwined each other, much like a spiral staircases, handrails on both sides is more than two nucleotide chain P gene sugar alternately with a skeleton, and pedal base is right. In the absence of accurate information on the X-ray, they also concluded that model is not entirely correct.

The next step is the scientific method to predict the basis of this model of the X-ray diffraction pattern with the experimental data for some serious comparison. They called once again invited Wilkins. Less than two days of work, Wilkins and Franklin used X-ray data analysis confirmed the double helix structure of the model is correct, and wrote a report also published two experiments in the United Kingdom "Nature" magazine. 1962, Watson, Crick and Wilkins received the Nobel Prize in Physiology and Medicine, and Franklin died of cancer death in 1958 and had not been granted the award.

Towards the late 1930s, Sweden's scientists to prove that DNA is symmetrical. After World War II, using electron microscopy of the DNA molecule is about 2 nm in diameter.

The double helix structure of DNA was discovered, greatly shocked the academia, inspiring people's minds. Since then, people immediately genetics for the Centre carried out a large number of molecular biology research. The first is around the four kinds of bases to encode what permutations and combinations can be expressed as 20 kinds of amino acids centres studied. 1967, the genetic code was cracked all the genes in the DNA molecular level so as to achieve new concept. It shows that: DNA gene is actually a fragment of macromolecules is controlling biological traits of the functional units of genetic material and structural units. In this unit on a number of nucleotide fragment is not arbitrary arrangement, but so as to the meaning of the password order. Some of the DNA structure can be controlled synthesis of the corresponding proteins. Protein is an important component of organisms, the organisms is mainly through the characters to reflect the protein. Therefore, the control of gene traits through DNA control protein synthesis. On this basis, have had a genetic engineering, enzyme engineering, fermentation engineering, protein engineering, biotechnology development will make use of the people of the benefit of mankind. The development of modern biology, more shows will lead to increased discipline for the trend.