DNA molecules are extremely large (generally, the molecular weight is at least one million), and the main components are adenine deoxynucleotide, guanine deoxynucleotide, cytosine deoxynucleotide and thymine deoxynucleotide. DNA exists in the nucleus, mitochondria and chloroplasts, and can also exist in the cytoplasm of some cells in a free state. Most known phages, some animal viruses and some plant viruses also contain DNA.
Except RNA and phage, DNA is the genetic material basis of all living things. The similarity and heredity between parents and children of organisms, that is, the so-called genetic information, are stored in DNA molecules. In 1953, james watson and francis crick described the structure of DNA: a pair of polynucleotide chains are twisted together to form a double helix. To this end, they shared the 1962 Nobel Prize in Physiology or Medicine with Frederic Wilkins, a physicist from National Institute of Technology in London.
The hero who discovered the double helix structure of DNA 50 years ago
Xinhuanet (2003-04-2316: 34: 41) Source: Beijing Daily.
1953 At noon on February 28th, two young scientists from Cambridge University, francis crick and james watson, walked into the Eagle Bar and announced their discovery: DNA is a double helix composed of two nucleotide chains.
This famous bar is located diagonally opposite King's College, Cambridge University. The symbol of the bar is an eagle spreading its wings, and its English name is Eagle Pub. Now there is a sign in front of the bar that introduces this history. At that time, Watson and Crick were both ordinary and even a little frustrated at Cambridge University. Watson is only 25 years old and Crick is only 37 years old. They even have one
It is difficult to find a formal occasion to announce the results. It always gives people a funny feeling to announce such an important discovery in a bar. Fortunately, Cambridge people were of high quality, and no one denounced them as crazy at that time. When Watson and Crick became famous, they received a grand reception when they came out to speak, but what they explained and announced was not as important as the discovery of DNA double helix structure.
Physicists' pamphlet "What is Life" has opened up a broad field of life science research.
The discovery of DNA double helix structure benefited from a popular science booklet "What is Life", written by Austrian physicist Schrodinger, one of the founders of quantum mechanics (1887-196 1).
For a long time, it has been found from many preliminary experiments that the heritability between organisms is determined by one factor, but it has never been known what determines this phenomenon. In the first half of the 20th century, many physicists turned their attention to the phenomenon of life, hoping to reveal the mystery of life from the material level. 1944, Schrodinger published a pamphlet "What is life", which expounded the importance of studying life phenomena from a new viewpoint of physics in popular language. He extended many new topics from the existing research results of biology, such as how to encode genetic information, and thought that it would be solved by physical and chemical methods in the end.
The publication of what is life has had a great influence on young scientists, and it is known as a pamphlet to arouse the biological revolution ideologically. Crick, who is studying for a Ph.D. in physics at Cambridge University, has read this pamphlet deeply and learned that physicists need to participate in the development of this vast field of biology. He was convinced that his knowledge of physics would contribute to the study of biology, so he resolutely turned to biology. Coincidentally. Watson (1928-), a young American scholar, was also influenced by What is Life. From the book, he realized that the key factor between atoms, molecules and the essence of life is genes, and predicted that people who can unlock the chemical and physical codes of genes carrying genetic information will become outstanding scientists.
At that time, biologists began to use the word gene freely to express the concept of the smallest unit of genetic information, but they still didn't know what a gene was. 195 1 In autumn, Watson first met Crick at Cambridge University. The two hit it off, met for a long time, and immediately began to cooperate, determined to find out what DNA is. At the beginning of 1953, Watson and Crick were inspired by the achievements of scientists at King's College London. Watson recalled: "Suddenly, my pulse quickened and my thoughts flooded. There is a picture in front of us: the structure of DNA is much simpler than many people think, and it should be spiral. "
However, the discovery of DNA double helix structure has not attracted much public attention. 1953 On April 25th, the British magazine Nature published this achievement. Twenty days later, Sir lawrence bragg, director of the Cavendish Research Office of Cambridge University, mentioned this discovery in a speech, which was reported by the media and aroused public concern. On the occasion of the 50th anniversary of this achievement, many countries are holding various commemorative activities, and the media also take this opportunity to carry out popular science work.
However, there is still debate about whether the birthday of this achievement is February 28th or April 25th of 1953. According to international academic practice, an achievement can only be officially published in academic magazines after peer review, so as to prevent confusion caused by someone taking advantage of loopholes to announce a major achievement casually. Therefore, although Watson and Crick announced this achievement in Eagle Bar on February 28th, many organizations, including British official organizations, celebrated the 50th anniversary of the discovery of DNA double helix structure on April 25th this year.
The mother of the double helix structure is rosalind franklin, a female scientist who didn't win the Nobel Prize.
1962, Watson and Crick, together with maurice wilkins, won the Nobel Prize for discovering the double helix structure of DNA. Wilkins' contribution is to provide experimental evidence for Watson and Crick's discovery. However, when I attended an event at King's College, Cambridge in March this year, a press officer of the British Council, the organizer, made a formal speech. When introducing the 50th anniversary of the discovery of DNA double helix structure, she got excited and said loudly: "We can't forget Rosie, who made great contributions in the process of discovering DNA double helix structure and should win the Nobel Prize!"
Female scientist rosalind franklin
This is a famous case in the history of science. Rosie is a female scientist at King's College, University of London, UK. Her full name is rosalind franklin (1920-1958). In the process of discovering the double helix structure of DNA, Watson said that the most critical inspiration was based on Franklin's achievements.
Franklin was an excellent experimental scientist. She got the image by X-ray diffraction of DNA crystal, so that she could distinguish the size, angle and shape of this molecule. She found that DNA is a spiral structure with at least two strands, and its chemical information faces inward. This is very close to the truth. However, Franklin was very individual and often criticized people bluntly. Watson and Crick were also tortured by her. In addition, in the 1950s, the xenophobia in British academic circles was serious, so Franklin, as a Jew and a woman, had a straightforward temper, which was naturally not tolerated by academic circles. So in 1962, when Watson and Crick won the Nobel Prize, she was not mentioned at all. The honor that should have belonged to her fell to her rival Wilkins at King's College London.
In the book "Double Helix" published by 1968, Watson revealed that Wilkins had secretly copied Franklin's research results and provided them to him, including the now-known X-ray images of her spiral structure. Without Franklin's X-ray achievements, it is almost impossible to determine the spiral structure of DNA.
Due to the long-term influence of X-rays, Franklin died of ovarian cancer on 1958 at the age of 37. The real reason why Watson and Crick didn't admit her contribution to DNA earlier is that they didn't tell her that they used her research results at all. Watson finally wrote with emotion: "Now it is necessary to explain what she has achieved ... Crick and I admire her integrity and generosity very much. It was many years before we gradually got to know this talented woman. She has been fighting for recognition from the scientific community for a long time, and the world often only regards women as a pastime after research work. When she realized that her life was dying, she didn't sigh or complain. Until a few weeks before her death, she spared no effort to work at the top. Franklin's brave spirit and noble quality are worth learning. "
Watson said today that genetic privacy and genetic discrimination are two serious problems in gene research and application.
Watson and Crick rarely show up now. At noon on April 14 this year, Dr. Francis Collins, head of the National Human Genome Research Program of the United States, solemnly announced that the human genome sequence map was successfully drawn and all the goals of the Human Genome Program were achieved. When james watson, one of the discoverers of DNA double helix structure, came to the Washington conference site, the gray-haired senior scientist immediately attracted the attention and welcome of the participants. Watson reviewed the history of gene research at the press conference and pointed out that gene privacy and gene discrimination are two serious problems in the field of gene research and application.
Looking back at history, we can see that the discovery of DNA double helix structure gave birth to molecular biology. In the past 50 years, life science and biotechnology have developed rapidly, and the human genome map and rice genome map have been successfully drawn. After Dolly 1996, a variety of cloned animals were born one after another, and some transgenic animals and plants have also entered the homes of ordinary people. This series of great achievements is a generous gift to the new century, marking another step in life science. It will promote the application of genome sequencing, functional gene research and gene technology, thus promoting the development of the whole biotechnology, and will also have a far-reaching impact on the development of science and technology, economic development and the whole society. In addition, life science research, including human itself, shows a bright future for human beings. While welcoming the new breakthroughs in life science, how to fully consider the possible negative effects of these breakthroughs and make them benefit mankind to the greatest extent has become an urgent task before us at the beginning of the new century.
A new milestone in life science: the discovery of DNA double helix structure
Xinhuanet (2003-04-23 16:43:30) Source: Science and Technology Daily.
Colorful and fascinating life phenomena have always been one of the most concerned topics. In the long history of exploring the mysteries of biology, groups of biologists struggled and devoted themselves to it, and raised the sail of "breaking the waves" of biology with outstanding contributions. Today, when we turn a page in the history of biological starry sky, we have to pay special attention to the outstanding contributions of Kim Watson and F Crick. Fifty years ago, it was these two great scientists who put forward the amazing discovery of DNA double helix structure model, which opened a new chapter in molecular biology. If Darwin's theory of evolution in the19th century is a milestone in revealing the law of biological evolution and promoting biological development, then the proposal of DNA double helix structure model is another milestone in opening a new stage of life science. As a result, mankind began to enter the journey of transforming and designing life.
It is true that every breakthrough in biological science is the product of its own development to a certain stage, and the result of mutual infiltration and integration of new theories and technologies in different disciplines, but there is no doubt that it is the precious crystallization of individual creative work of scientists first. Today, understanding the background and conditions of DNA double helix structure model and its positive influence on biological development is of great benefit for us to deeply understand the scientific value of this great discovery and correctly grasp the law and direction of modern life science development. It is based on this understanding that the author wrote this essay to commemorate the 50th anniversary of the DNA double helix structure model.
Although the complicated creatures vary widely, no matter what you throw. What if the young plutonium "conspires" with the local chain to steal water? Hey? Have you lost yourself? Badger's tip garden is inflamed, and the drought-stricken people are rushing to Huai? Pregnant? Hey? What about chlorine? 芤芩 shape? Cyst? So dear? Hey? Hey? What's the matter with you? Crowbar? ヒ Bohuan? His theft? Dad, is it bad luck? Is the ditch dry? Throw cherry blossoms? What happened? What's the matter with you? Is the machine irritable or even? ⑽? Iridium? Glutinous? 1. Huh? War? What's wrong with sheen? Α?
At the end of 17, some people put forward the view of "pre-formation theory", arguing that the main reason why organisms can pass on their own traits to their offspring is that the sex cells (sperm or egg cells) contain a tiny new individual embryo in advance. Purists believe that this "microorganism" exists in sperm; Oogonists believe that this "microorganism" exists in eggs. But this view was quickly overturned by facts. Because, no matter in sperm or eggs, people simply can't see this "embryonic form". On the contrary, German embryologist Wolff put forward the "evolution theory". He believes that any tissues and organs of living things are gradually formed in the process of individual development. But what is the manipulator of genetic variation? Remains a mystery.
It was not until 1865 that Austrian geneticist Mendel put forward the concept of "genetic factor" (later called gene) for the first time when expounding the separation rule and free combination rule he discovered, thinking that it exists in cells and is the material basis for determining genetic traits.
1909, Danish botanist Johnson replaced Mendel's "genetic factor" with the word "gene". Since then, genes have been regarded as the decisive factor of biological traits and the basic unit of the structure and function of biological genetic variation.
1926, American geneticist Morgan published the famous "Gene Theory". He and other scholars used a lot of experiments to prove that genes are the genetic units that make up chromosomes. It occupies a certain position and space on the chromosome and is arranged in a straight line. In this way, Mendel's hypothesis about genetic factors falls on the specific genetic material-gene, which lays a theoretical foundation for further study on the structure and function of gene.
Nevertheless, people didn't know what kind of substance genes were at that time. It was not until the 1940s that scientists made it clear that nucleic acids, especially deoxyribonucleic acid (DNA for short), were the genetic material of all living things that the word gene had an exact content.
195 1 year, scientists got DNA crystals in the laboratory;
X-ray diffraction pattern of DNA was obtained in 1952, and it was found that virus DNA could replicate virus particles after entering bacterial cells. ...
During this period, two things about the double helix structure of DNA were discovered, which played a direct role in "promoting". First, Professor Sanger of the University of California discovered the spiral structure of protein molecules, which gave people important enlightenment; First of all, X-ray diffraction technology has been effectively applied to the study of the structure of biological macromolecules, providing a decisive experimental basis.
It is under such scientific background and research conditions that American scientist Watson came to Cambridge University in England to work with British scientist Crick to study the structure of DNA. Through the analysis and research of a large number of X-ray diffraction materials, they put forward the double helix structure model of DNA, which was officially published in the British magazine Discovery on April 25th, 1953, and thus established the genetic code and template theory.
After that, scientists continued to study the structure and function of DNA and made a series of significant progress. 196 1 year, they successfully cracked the genetic code, and confirmed the correctness of the double helix structure of DNA with irrefutable scientific basis, so that Wolin, Crick and Wilkins won the 1962 Nobel Prize in Medical Physiology.
Modern biological research has made it clear that nucleic acid is a biomacromolecule composed of many nucleotides. There are four main types of nucleotides, which are arranged in different orders to form nucleic acid molecules containing various genetic information. Genes are nucleotide fragments containing specific information in nucleic acid molecules (mainly DNA).
At the same time, a large number of life phenomena in nature and many experimental results in experiments also give biologists useful enlightenment.
For example, Escherichia coli is a large family with many strains and tens of thousands of different types. Some strains lack genes to guide the synthesis of some special nutrients, and they must take these nutrients directly from the culture medium to survive. These Escherichia coli are called auxotrophs. For example, E.coli K cannot synthesize threonine (T) and leucine (L); However, its other strain does not have the ability to synthesize biotin (b) and methionine (m). Neither of these two kinds of Escherichia coli can grow alone in the medium lacking TLBM. However, when these two kinds of E.coli are mixed together and put on the medium lacking the above four substances, new colonies miraculously grow. What is the reason? As mentioned earlier, E.coli K lacks T and L genes, but contains B and M genes. On the other hand, the DNA of another strain contains two genes, T and L, which K lacks, although it does not have B and M genes. When they are co-cultured in large quantities, the DNA in the cells of the former strain may enter the cells of the latter strain through the cell membrane, so that the two types of DNA can be recombined to form a new type of Escherichia coli containing four BMTL genes at the same time. In fact, the above-mentioned phenomenon of hybridization between bacteria can not only be carried out in the nutrition deficiency experiment specially designed by biologists, but also exist in many bacteria in natural state, but the number is too small to be easily found.
The above-mentioned DNA transfer is mainly achieved through the contact between cells, without the help of external forces. However, there is another situation in which the transfer and recombination of DNA is completed with the intervention of a third party. Such as phage transduction is a typical example.
Phage is a virus that infects bacteria and actinomycetes. It is small in size and simple in structure. In addition to the hexagonal head containing DNA, it is covered with a protective shell and a tadpole-shaped tail. When infected with bacteria, lysozyme is secreted from its own tail to dissolve the cell wall somewhere inside the bacteria, and then the DNA from the head is sent into the bacteria through this gap. There are two types of processes in which bacteriophages infect bacteria. One is called severe infection, that is, the phage DNA of invading bacteria immediately replicates itself, producing new DNA and protein shell, and then secreting lysozyme to rupture the cell wall of bacteria and release new phage; The other is mild infection, that is, phage DNA does not replicate itself immediately after entering bacterial cells, but is inserted into the chromosomes of infected bacterial cells to lurk. Bacterial chromosomes are replicating themselves at the same time, and quietly enter daughter cells with chromosomes. However, when exposed to external stimuli such as ultraviolet rays, the DNA of temperate bacteriophages will immediately break away from bacterial chromosomes and replicate rapidly, thus cracking bacteria and releasing new bacteriophages. Biologists infect Salmonella flagellatus with mild phage, promote the rapid replication of phage DNA invading bacteria through ultraviolet irradiation, release mature phage, and then infect Salmonella flagellatus with it to produce flagellate bacteria. The reason is that when temperate bacteriophage infects Salmonella flagellae and replicates itself, it mistakenly wraps the DNA fragment that determines flagella characteristics in bacterial cells in its protein shell. When they infect Salmonella flagellae again, it brings this DNA fragment that determines flagella characteristics into Salmonella flagellae, which leads to a strange thing, that is, flagella bacteria grow flagella. This phenomenon is called "transduction phenomenon". This experiment not only proves once again that DNA in biological cells can be transferred from one cell to another, but also shows that phage is an ideal carrier in the process of realizing this transfer.
Since DNA is the main genetic material that determines biological characteristics, DNA transfer and recombination exist in nature, and vectors of genes such as bacteriophages exist, can we try to isolate DNA molecules from different biological cells and cut them in vitro to obtain some specific genes we need? Or artificially synthesize some gene fragments, then recombine the genes according to the pre-designed scheme, and send the recombinant weight back to the cells of the organism through certain means of transportation, and express its function, so as to break through the barriers of distant hybridization, transform the organism and create new varieties according to human will?
As mentioned above, Escherichia coli is one of the most common microorganisms. The plasmid in the cytoplasm of Escherichia coli is a kind of circular DNA, which is easy to enter and leave the cell. In addition, it is simple in structure, fast in reproduction and easy to cultivate, so Escherichia coli naturally becomes the object of genetic engineering research and an ideal operating tool. 1969, American biologist Shapiro and others first artificially isolated genes from plasmid circular DNA fragments of Escherichia coli by biological methods. Three years later, American scientist Cohen isolated two plasmids of E.coli from cells for the first time, recombined the DNA molecules in the plasmids in vitro, and then sent them back to E.coli for successful expression, thus realizing gene manipulation for the first time.
Since then, genetic engineering has developed in full swing and made exciting breakthroughs, just like a magnificent star Ran Ran rising above science, which is fascinating. Today, we can use genetic manipulation to break through interspecific barriers and realize the recombination of various biological genetic traits. Genetic engineering has become the core technology of biotechnology, which is widely used in medical and health care and various industrial fields. Looking forward to the future, its role in benefiting mankind is infinite. The prospect is attractive and there is a long way to go. Let's work hard for it! (Xu Jiuwu)