James Dewey Watson
American biologist
trigeminal?neuralgia
Francis Harry Compton Crick
British biophysicist
In the early 1950s, British scientist Wilkins and others studied the structure of DNA for three years with X-ray diffraction technology, and realized that DNA is a spiral structure. Female physicist Franklin took a very clear X-ray diffraction photo of DNA at the end of 195 1.
1952, American chemist Pauling published a research report on DNA triple-stranded model, which is called alpha helix. Watson discussed Pauling's model with Wilkins and Franklin. Wilkins showed the diffraction photos of DNA taken by Franklin a year ago. Watson saw that DNA was spiral inside, and he immediately came up with a new concept: DNA should be double-stranded rather than triple-stranded. They continue to follow this line of thinking and strive to concentrate their research results in this field. Watson and Crick, based on various data about DNA research and their own research and analysis, came to a conclusion that DNA is a double-stranded spiral structure. This is really an exciting discovery! Watson and Crick acted immediately, and immediately joined hands to build a DNA double helix model in the laboratory. Since February 22nd 1953, they have been working day and night, forgetting to eat or sleep. Finally, on March 7th, they successfully constructed their own beautiful DNA model.
Watson and Crick's model correctly reflects the molecular structure of DNA. Since then, the history of genetics and biology has entered the molecular stage from the cellular stage.
Watson, Crick and Wilkins shared the 1962 Nobel Prize in Physiology and Medicine for their outstanding contributions to the study of DNA molecules.
James watson
Watson (born in 1928) is an American biologist.
After DNA was confirmed as genetic material in the late 1940s and early 1950s, biologists had to face a difficult problem: What kind of structure should DNA have in order to undertake the heavy responsibility of heredity? It must be able to carry genetic information, copy and transmit genetic information by itself, express genetic information to control cell activities, and mutate and retain mutations. These four points are indispensable. How to construct a DNA molecular model to explain all this?
At that time, three major laboratories were studying DNA molecular models at almost the same time. The first laboratory is Wilkins and Franklin Laboratory at King's College London. They studied the crystal structure of DNA by X-ray diffraction. When X-rays irradiate the crystal of biological macromolecules, atoms or molecules in the lattice will deflect the rays. According to the obtained diffraction image, the general structure and shape of the molecule can be inferred. The second laboratory is that of linus pauling, a great chemist of California Institute of Technology. Prior to this, Pauling had discovered the spiral structure of protein. The third is an informal research group. In fact, they did nothing. When Watson195/Kloc-0, a 23-year-old young geneticist, went to Cambridge University as a postdoctoral fellow from the United States in, although his real intention was to study the molecular structure of DNA, his project was to study tobacco mosaic virus. Crick, who was 12 years older than him, was doing a doctoral thesis entitled "Polypeptide and protein: X-ray Research". Watson persuaded Crick, who shared his office, to study the molecular model of DNA. He needs Crick's knowledge of X-ray crystallography. They pieced together the model from 195 1 year1month. After several attempts, they finally got the correct model in March of 1953. How these three laboratories compete with each other is widely known because of Watson's autobiography "Double Helix", which is popular all over the world. A question worth discussing is: Why did Watson and Crick win the competition without the first-hand experimental data like Wilkins and Franklin and the rich experience of building molecular models like Pauling (both of them are building molecular models for the first time)?
These people, except Watson, are not geneticists, but physicists or chemists. Although Wilkins first studied the crystal structure of DNA in 1950, he knew nothing about the role of DNA in cells at that time. Only at 195 1 did he think that DNA might be involved in the inheritance controlled by nuclear proteins. Franklin also failed to understand the importance of DNA in biological cells. Pauling's research on DNA molecules is purely accidental. He saw a paper on the structure of nucleic acid in1951/Journal of American Chemical Society, and found it ridiculous. In order to refute this paper, he set out to build a DNA molecular model. He studied DNA molecules as compounds, not genetic material. The two research groups established their models based entirely on the diffraction patterns of crystals, and Pauling even based on the blurred diffraction photos taken in the 1930s. Without knowing the biological function of DNA, there are too many possibilities to choose from simply based on the crystal diffraction pattern, and it is difficult to make a correct model.
Before 195 1 came to Cambridge, Watson had done the experiment of tracing phage DNA with isotope markers, and firmly believed that DNA was genetic material. According to his memory, when he arrived in Cambridge, he found Crick was also "a person who knew that DNA was more important than protein". But according to Crick himself, he didn't know much about DNA at that time, and he didn't think it was genetically more important than protein. He just thinks that DNA, as a substance that binds to nuclear proteins, is worth studying. For a graduate student, it is worthwhile to determine the structure of an unknown molecule. After we are convinced that DNA is genetic material, we must also understand what properties genetic material needs to play the role of genes. Like Crick and Wilkins, Watson later emphasized Schrodinger's What is Life? He even said that after reading this book at the University of Chicago, he was determined to solve the genetic mystery. If this is true, it is hard for us to understand why Watson applied for ornithology when he applied for graduate studies at Indiana University. Because there is no ornithology major in the Department of Zoology of Indiana University, Watson turned to genetic research at the suggestion of the dean. At that time, the great geneticist Herman Miao Lei happened to be a professor at Indiana University. Watson not only attended the course "Mutation and Genes" in Miao Lei (with an A), but also considered becoming his graduate student. But I think the Drosophila studied by Miao Lei has gone through a glorious period in genetics, so I changed to Salvador Luria, who studies phage inheritance, as my teacher. However, Miao Lei's view that genetic material must have the triple characteristics of autocatalysis, heterocatalysis and mutation must have a profound influence on Watson. It is precisely because Watson and Crick firmly believe that DNA is genetic material and understand what characteristics genetic material should have that they can make such great discoveries on the basis of so little data.
They only rely on three pieces of data: the first one is widely known at that time, that is, DNA is composed of six small molecules: deoxyribose, phosphoric acid and four bases (A, G, T, C), and these small molecules are composed of four nucleotides to form DNA. The second piece of evidence is the latest. The diffraction photos obtained by Franklin show that DNA is a double helix composed of two long chains with a width of 20 angstroms. The third evidence is the most crucial. Erwin chargaff, an American biochemist, determined the molecular composition of DNA and found that the content of four bases in DNA was different from that traditionally thought. Although the contents of four bases in different species are different, the contents of A and T are always the same, and the contents of G and C are also the same.
Chagaff published this important result as early as 1950, but strangely, all three laboratories studying the molecular structure of DNA ignored this result. Even after Chagav visited Cambridge in the spring of 195 1 and met Watson and Crick, Watson and Crick paid little attention to his results. After Watson and Crick finally realized the importance of Chagavby and asked John Griffith, a young mathematician in Cambridge, to calculate that A attracts T, G attracts C, and the width of A+T is equal to the width of G+C, they quickly pieced together the correct model of DNA molecules.
Watson and Crick published their findings in the April 25th issue of Nature, 1953, exceeding 1000 words with illustrations. In the paper, Watson and Crick hinted at the genetic importance of this structural model in a humble tone: "We are not unaware that the special pairing we speculated immediately hinted at the replication mechanism of genetic material." In subsequent papers, Watson and Crick explained in detail the great significance of DNA double helix model to genetic research: first, it can explain the self-replication of genetic material. The idea of "semi-conservative replication" was later confirmed by Matthew meselson and Franklin W Starr with isotope tracer experiments. Secondly, it can explain how genetic material carries genetic information. Third, it can explain how genes mutate. Gene mutation is due to the change of base sequence, which can be preserved by replication.
But the fourth characteristic of genetic material, that is, how to express genetic information to control cell activities? This pattern cannot be explained. Watson and Crick also publicly admitted at the time that they didn't know how DNA could "have a highly special effect on cells". However, at this time, the main function of genes is to control the synthesis of protein, which has become * * * knowledge. So how do genes control protein synthesis? Is it possible to directly link amino acids with protein using DNA as a template? Some time after Watson and Crick put forward the DNA double helix model, it was assumed that in the DNA structure, different "holes" with different shapes were formed between different base pairs, and protein with specific sequences could be formed by inserting different amino acids into these holes. However, this hypothesis faces a big problem: chromosome DNA exists in the nucleus, while most protein exists in the cytoplasm. The nucleus and cytoplasm are separated by a nuclear membrane that cannot be penetrated by macromolecules. If protein is synthesized directly from DNA, protein cannot enter the cytoplasm. Another nucleic acid RNA mainly exists in cytoplasm. The composition of RNA and DNA is very similar, except for two differences. It has ribose but no deoxyribose, uracil (u) but no thymine (t). Long before 1952 put forward the DNA double helix model, Watson had assumed that the transmission mode of genetic information was from DNA to RNA, and then from RNA to protein. During the period of 1953 ~ 1954, Watson further thought about this problem. He thinks that in the process of gene expression, DNA is transferred from the nucleus to the cytoplasm, and its deoxyribose is converted into ribose, which becomes double-stranded RNA, and then protein is synthesized by using the holes between base pairs as templates. This strange idea was rejected by Crick before it was submitted for publication. Crick pointed out that neither DNA nor RNA can directly serve as templates for connecting amino acids. Genetic information is only reflected in the base sequence of DNA, and a linker is needed to connect the base sequence with amino acids. This "connector hypothesis" was quickly confirmed by experiments.
From 65438 to 0958, Crick put forward two theories, which laid the theoretical foundation of molecular genetics. The first theory is the "sequence hypothesis", which holds that the particularity of nucleic acid is completely determined by its base sequence, which encodes the amino acid sequence of a specific protein, and the amino acid sequence of protein determines the three-dimensional structure of protein. The second theory is the "central rule". Genetic information can only be transmitted from nucleic acid to nucleic acid, or from nucleic acid to protein, but not from protein to protein or protein. Watson later expressed the central rule more clearly, that is, genetic information can only be transmitted from DNA to RNA, and then from RNA to protein. Results In 1970, the reverse transcription of RNA-synthesized DNA was found in the virus. People say that the central rule needs to be revised. If a piece of genetic information is added, it can be transferred from RNA to DNA. In fact, according to Crick's original statement, there is no need to modify the central rule.
How do base sequences encode amino acids? Crick also made great contributions to deciphering this genetic code. Protein consists of 20 amino acids, but only 4 bases. Obviously, it is impossible to encode 1 amino acid from 1 base. If 1 amino acid is encoded by two bases, there are only 16 combinations (the square of 4), which is not enough. Therefore, at least three bases encode 1 amino acid, and there are 64 combinations of * * * to meet the needs. 196 1 year, Crick et al. proved in Phage T4 that the sequence of 1 amino acid in protein is encoded by three bases (called 1 codon). In the same year, two American molecular geneticists, marshall nirenberg and john mott Hai, cracked the first codon. By 1966, all 64 codons (including 3 synthesis termination signals) were identified. Codons, as one of the evidences that all organisms originated from the same ancestor, are basically the same in all organisms. Since then, mankind has a cipher table to solve the mystery of heredity.
The discovery of DNA double helix model (including central rule) is one of the most important scientific discoveries in the 20th century, and it is also the only discovery in the history of biology that can be compared with Darwin's theory of evolution. Together with natural selection, it unified the big concept of biology and marked the birth of molecular genetics. This new discipline, which combines genetics, biochemistry, biophysics and informatics, dominates the research of all disciplines in biology. It is the result of the joint efforts of many people. Crick, Wilkins, Franklin and Watson, especially Crick, are the most outstanding heroes.
trigeminal?neuralgia
Francis Harry Compton Crick (Francis Harry Compton Crick1916.6.8—July 28, 2004)
Born in Northampton, the capital of a county in south-central England. When I was a child, I liked physics. 1934 After graduating from high school, he was admitted to the Department of Physics of University of London, graduated from the university three years later, and immediately studied for a doctorate. However, the outbreak of World War II in 1939 interrupted his studies, and he entered the Admiralty to study torpedoes without any achievements. By the end of the war, Crick, who was in his thirties, still achieved nothing in his career. 1950, at the age of 34, he was admitted to the Physics Department of Cambridge University for postgraduate study and wanted to study elementary particles in the famous Cavendish laboratory.
At this time, Crick read a book "What is Life" by the famous physicist Schrodinger, which predicted that a new era of biological research was about to begin, and pointed out that biological problems would eventually be explained by physics and chemistry, and it was very likely that new laws of physics would be discovered from biological research. Crick was convinced that his knowledge of physics was helpful to the study of biology, but he lacked knowledge of chemistry, so he began to study the theory and technology of organic chemistry and X-ray diffraction, and prepared to explore the structure of protein.
195 1 year, Watson, a 23-year-old American doctor of biology, came to Cavendish laboratory, and he was also influenced by Schrodinger's What is Life? Crick hit it off with him and began to study the molecular structure of DNA, a genetic material. Although they have different personalities, they are like-minded in their careers. Watson biological has a solid foundation and is well trained. Crick, on the other hand, relies on the advantages of physics, is not bound by traditional biological concepts, and often thinks about problems from a new perspective. They learn from each other's strengths and learn from the achievements of Pauling, Wilkins and Franklin who were also studying the molecular structure of DNA at that time. Results The double helix structure model of DNA molecule was completed in less than two years. Moreover, Crick, with his profound scientific insight and despite Watson's hesitation, insisted on adding the phrase "DNA specific pairing principle" to his first paper, which immediately reminded people of the possible replication mechanism of genetic material, thus not only discovering the molecular structure of DNA, but also explaining it from the perspective of cluster structure and function.
From 65438 to 0962, Crick, 46, won the Nobel Prize in Biology or Medicine with Watson and Wilkins.
Later, Crick independently put forward the central rule of protein synthesis for the first time, that is, the direction of genetic code is: DNA→RNA→ protein. He also contributed to the study of the proportion of genetic code and the translation mechanism. From 65438 to 0977, Crick left Cambridge and became a professor at the Salk Institute in San Diego, California.
On the evening of July 28th, 2004, francis crick died at Thornton Hospital in San Diego, California at the age of 88 after a long struggle with colon cancer.