Discovery of DNA

Since Mendel's laws of genetic re-discovered, it also raises the question: is the genetic material is not an entity? In order to solve the problem of what genes are, the people of nucleic acids and proteins.
As early as 1868, people have been found in nucleic acids. Chemists in Germany Hoppe Sailor's lab, a graduate of the Swiss(1844 - 1895), his lab near a hospital threw the bandage with blood of the very sense of Interest, because he knows that those blood to defend human health, germs and "combat" and was killed in action and kill white blood cells of the human body "remains." He carefully put a bandage on the blood collected and used for decomposition of pepsin, and found the bodies of most of the cells break down, but on the nuclear non-functional. He further on the nuclear material within an analysis and found that the nucleus contains a phosphorus and nitrogen-rich material. Hoppe sail with yeast experiments to prove that the material inside the nucleus of the Mitchell findings are correct. He would like to give this separate from the nuclear material is known as "nuclide", was later found that it was acidic, so to be called "nucleic acid." Since then, people have carried out a series of effective nucleic acid.
In the early 20th century, Germany Ke Saier (1853 - 1927) and two of his students Jones (1865 - 1935) and Levin (1869 - 1940) study, understand the basic chemical structure of nucleic acids, it Is composed of a number of nucleotide molecules. By nucleotide base pairs, consisting of phosphate and ribose. There are 4 kinds of bases in which (Yin cast a glance gland, Yin guanine, thymine and cytosine), there are two ribose (ribose, deoxyribose), the nucleic acids into RNA (RNA) and deoxyribonucleic acid (DNA) .
Levin made his rush to the results of research, mistakenly believe that 4 in the nucleic acid bases in the volume is equal, so as to derive the basic structure of nucleic acids by 4 with different nucleotide bases to connect into a four-nucleoside Acid as a basis for nucleic acid into a polymer, a "four-nucleotide hypothesis." This hypothesis wrong, understanding of the complex structure of nucleic acids from the considerable obstacles, to a certain extent affected the people's understanding of the functions of nucleic acids. It is believed that although the nucleic acid present in the structure of the important - nuclear, but its structure is too simple, it is hard to imagine in the process of genetic What role.
Protein nucleic acid than found as early as 30 years, has developed rapidly. Of the 20th century, composed of 20 amino acid protein has been found to be 12, 1940, the whole was found.
In 1902, a German chemist Xie Erti charges between amino acid peptide chain link and the theory of the formation of proteins, in 1917, he was synthesized by the glycine-15 leucine and 3 of the 18 components of long-chain . As a result, some scientists the idea, is likely to be genetic in the protein plays a major role. If the nucleic acids involved in genetic, protein and must be linked to the role of the protein. As a result, at that time generally tend to think that biological protein is the carrier of genetic information.
In 1928, American scientists Griffith (1877 - 1941) with a capsule, and a strong toxic-free capsule, low toxicity of the pneumococcus experiments on rats. To have He pods high temperature to kill bacteria with no along with pods of live bacteria were injected mice, he found that the incidence of death soon rats, mice at the same time he's in the blood of the isolated bacteria living there pod. This shows that even without passing bacteria from the dead bacteria in the pod have access to what material to make a risk-free bacteria into bacteria have a pod. Assuming that the right thing to do? Griffith in a test tube experiment and found the dead bacteria with the United States are living without passing on the bacteria test tube train at the same time, without passing all the bacteria have become a pod bacteria and found so that no bacteria long pod A protein of the scare is there a risk of dead bacteria in the shell left over from the nucleic acid (as in heating, the pod of nucleic acid has not been damaged). Griffith said the nucleic acid as a "conversion factor."
In 1944, the United States Avery bacteriologist (1877 - 1955) from the United States and bacteria have been isolated activity of the "conversion factor", and that such material did a test of the existence of protein test, the results were negative, and to prove "Conversion factor" is the DNA. But this has not been found in a wide range of recognition, it is not suspected at the time of the technology in addition to net protein, the protein residues into play.
German-American scientists Delbruck (1906 - 1981) of phage group has a firm belief that Avery's discovery. Because they observed under the electron microscope of the phage into the shape and growth of E. coli. Phage bacterial cell is a host for the virus, individual small, with only the electron microscope to see it. It is like a small tadpole, the external components of the protein by the end of the first film and the sheath, the head of the internal contain DNA, the end of the end of silk sheath there, the substrate and the small hook. When the phage infection of E. coli, the tail end of the first bar in the bacterial cell membrane, and then it will be all the body's DNA were injected into bacteria cells, the protein shell remain in the bacterial cell outside, not from what the role of the . After the bacteria enter the cells of the phage DNA, on the use of bacterial material and rapid synthesis of the phage DNA and proteins, so many copy of the original size of the display exactly the same shape of a new phage until the bacteria were completely disintegrated, leaving only those phage dead bacteria , And then infect other bacteria.
In 1952, key members of the phage group Hershey (a 1908) and his students use the Chase advanced isotope labeling, so the E. coli bacteriophage experimental infection. He coli T2 phage DNA markers on 32P, the protein shell markings on 35S. Marking the first use of phage T2 E. coli infection, and then be separated from the results of the phage will be marked with 35S shell out to stay in E. coli, only the internal display with a 32P labeled nucleic acid were injected all the E. coli and E. coli within Phage successful breeding. The DNA test to prove there is transmission of genetic information of the functions of proteins and DNA by the synthesis of the directive. The result was immediately accepted by the academic community.
Almost at the same time, Austria biochemist Chargaff (1905 -) of the nucleic acid bases in 4 of the content of the outcome of the re-determination has been made. Avery in the work, if he thought the different species is due to the different DNA, the DNA structure must be very complicated, or difficult to adapt to biological diversity. As a result, he was out of the text "four nucleotide hypothesis," have had a doubt. In the 1948 - 1952 4 years, he made use of Levin times more than the precision of paper chromatography separation of 4 base pairs, with UV absorption spectra to do quantitative analysis, after repeated the experiment many times, and finally arrive at a different Levine. The results show that DNA molecules in purine and pyrimidine equal to the total number of elements, of which purine A gland and an equal number of T thymine, guanine and cytosine G Yin C equal to the number. Description of the DNA molecule A base with T, G and C is the existence of the match, which negates the "four nucleotide hypothesis", as well as to explore the molecular structure of DNA provides an important clue and based on.
April 25, 1953, the United Kingdom's "Nature" magazine published in the United States of Watson and Crick of the British University of Cambridge in cooperation with the results of research: DNA double helix model of the molecule, known as the outcome of the later 20 Century biology's greatest discoveries marked the birth of molecular biology.
Watson (1928 A) in middle school is an extremely intelligent children, 15-year-old when they entered the study at the University of Chicago. At that time, because of a person to allow an earlier study of the experimental sex education programs so that Watson had the opportunity to complete all aspects from the study of biological science courses. At the university, although Watson in genetics have little formal training, but since reading the Schrodinger's "What is life? - The physical appearance of living cells, "which prompted him to" find the genetic secrets. " He was good at brainstorming to win many long, good at using other people's ideas to enrich themselves. As long as there are convenient, do not have to force yourself to a whole new field of study, can be required knowledge. 22-year-old Watson made a doctorate, and then was sent to Europe to pursue post-doctoral researcher. In order to fully understand a gene's chemical structure of the virus, he went to study chemical laboratory in Copenhagen, Denmark. On one occasion he went to Naples, Italy, tutor to take part in a meeting of biological macromolecules, have the opportunity to listen to the British biologist physical Wilkins (1916 -) speech, Wilkins saw the DNAX-ray diffraction photograph. Since then, to find the key to unlock the structure of DNA in Watson's idea in the minds of the return. What can learn X-ray diffraction analysis of this map? So he went to Britain to study at the University of Cambridge Cavendish Laboratory, during which Watson understanding of the creek.
Crick (1916-2004) when high school passion for science, and in 1937 graduated from the University of London. In 1946, he read "What is life? - The physical appearance of living cells ", is determined to use the knowledge of physics to the study of biology, from biology to the interest. In 1947 he re-started the post-graduate study, in 1949, he Perutz used in conjunction with the X-ray study of the technical structure of the protein molecule, so this has been met with Watson. Watson, Crick was more than 12-year-old major, has not yet obtained a doctoral degree. However, very speculative to talk about them, Watson here are actually able to find how a protein is more important than DNA, is Sanshengyouxing. At the same time, Watson was in contact with his people, the creek is one of the most intelligent. They talked every day for at least a few hours to discuss academic issues. The two were complementary with each other to criticize each other, as well as stimulate each other's inspiration. They do not think the answer is to open the molecular structure of DNA genetic key to the mystery. With only the precise X-ray diffraction data in order to more quickly identify the structure of DNA. In order to get DNAX-ray diffraction, Crick invited Wilkins to come to Cambridge for the weekend. In the conversation Wilkins accepted the spiral structure of DNA point of view, but also his partner Franklin (1920-1958, F), as well as lab scientists also have been thinking very hard with the problem of DNA structure model . From from November 1951 to April 1953 for 18 months, Watson, Crick and Wilkins and Franklin are among several important academic exchanges.
In November 1951, after listening to Franklin Watson on the structure of the DNA of a more detailed report, inspired by a certain knowledge of the crystal structure analysis of Watson and Crick realized that in order to quickly establish the structure of DNA model, only Be able to use other people's analysis of the data. They quickly made a three-helical structure of DNA idea. By the end of 1951, they invited Wilkins and Franklin to discuss this model, Franklin pointed out that the water content of their DNA to less than half do so for the first time to set up the model failed.
One day, Watson went to King's College laboratory Wilkins, Wilkins Franklin recently beat out a system of "B-" DNA of the X-ray diffraction photograph. Watson saw pictures of them at once exciting, heart rate has accelerated, such as images than ever before to be the "A" is much more simple, as long as a little look at the "B-" X-ray diffraction photograph, and then by a simple calculation, Will be able to determine the number of DNA molecules in the number of nucleotide chains.
Please help Crick mathematician calculated results show that the source has attracted Yin Fu. According to their results from the Chargaff and got the two nucleic acid purine and pyrimidine two 22 equal As a result, the formation of the concept of base pairs.
They desperately to think of the 4 base sequence, time and again drawing on paper-base structure, playing with the model, repeatedly made the assumption that time and again to overthrow their own assumptions.
Watson (left) and there is a creek, according to Watson in the idea of playing with their own model, he shifted base to search for the removal of all kinds of matching. Suddenly, he found two hydrogen bonds linking the gland Yin-fat thymine and went so far as to the hydrogen bond of 3-connected guanine cytosine-Yin of have the same shape, so it boosted the spirit. Because the number of purine and pyrimidine why the number should be exactly the same as the mystery solved. Chargaff all of a sudden it became the law of DNA double helix structure of the inevitable result of the. As a result, how the chain as a template synthesis of another complementary sequence of bases is not hard to imagine the chain. In that case, the skeleton of the two chains must have the opposite direction.
After Watson and Crick tension in a row, quickly completed a metal model of DNA assembly. From this model to see, DNA from the two components of nucleotide chains, which along with the central axis of intertwined with each other in the opposite direction, much like a spiral staircase handrails on both sides is more than 2 nucleotide chains P-glycoprotein gene combined with the turn of the skeleton, and the pedal base is right. In the absence of accurate information on X-ray, they dare not conclude that the model is entirely correct.
Franklin Wilkins is the next step of the scientific method to predict based on the model of the X-ray diffraction pattern with the experimental data to make a serious comparison. They called once again invited Wilkins. Less than two days of work, Wilkins and Franklin used X-ray analysis of the data confirmed the double helix structure of the model is correct, and has written two experiments at the same time the report published in the UK "Nature" magazine. In 1962, Watson, Crick and Wilkins received the Nobel Prize for Physiology and Medicine, and Franklin died of cancer death in 1958 have not been awarded the prize.
In the late 1930s, the Swedish scientists on the DNA to prove it is asymmetrical. After the Second World War, with the electron microscope determination of DNA's molecular diameter of about 2nm.
Double helix structure of DNA was discovered, greatly shocked the academic community, inspired by the people's minds. From then on, people immediately in order to carry out genetics as the center of a large number of molecular biology research. First of all, around the base of 4 how to encode permutation and combination can show 20 kinds of amino acids for the Center for Experimental Research. In 1967, were cracking the genetic code, DNA in the genes so as to the molecular level to be a new concept. It shows: gene DNA molecules is actually a fragment, biological control is a trait of the genetic material of the functions and structure of the units units. The unit in a number of nucleotide fragments on the order is not arbitrary, but there are implications of the order of the password. A certain structure of the DNA, can control the structure of the corresponding protein synthesis. Protein is an important component of the composition of the organisms, the organisms are the main characters to reflect the adoption of the protein. As a result, the genetic traits of control through DNA control of protein synthesis to be achieved. On this basis, one after another have had a genetic engineering, enzyme engineering, fermentation engineering, protein engineering, the development of biotechnology is bound to make use of the law for the benefit of mankind. The development of modern biology, the more it will show up to take the lead for the subjects.