Who discovered the structure of DNA. Inventions and discoveries
Penetrating deeper and deeper into the secrets of the universe, man tried to answer one of the main questions that were asked by the ancient sages: what is life, what is man himself? The mystery of the birth of living organisms interested scientists no less than the structure of stars. The discoveries in the field of biology made in the 20th century brought humanity to new frontiers and outlined truly fantastic prospects. Molecular biology is still one of the most promising sciences of our time.
Having developed the theory of the evolution of living organisms, Darwin could not answer the question of how the changes in the structure and functions of living organisms that arose in the process of this evolution are fixed in the offspring. But when his book was just out of print, Gregor Mendel was already setting up his experiments in the Czech Republic. His conclusions marked the beginning of the development of the science of heredity - genetics, which was destined to explain the most important mysteries of the universe. On the pea model, Mendel first established the existence of special "hereditary factors" (later called "genes"), transmitted from one generation to another, while transferring certain traits. However, for a long time the transmission mechanism itself was unknown to scientists.
At the same time, the zoologist August Weismann worked in Germany, who expressed and proved the correctness of the opinion that the transfer of parental properties to offspring depends on the direct transfer of some material substance by the parents, which, according to Weismann, was enclosed in chromosomes - cell organelles. The most important research for the development of genetics was later carried out by the American Thomas Morgan. Having put a lot of experiments on fruit flies, he and his colleagues came to conclusions about the material foundations of heredity, the linear localization of genes in chromosomes, the patterns of their mutational variability, the cytogenetic mechanism of their hereditary transmission, etc., which made it possible to finalize the basic principles chromosome theory heredity.
In 1869, the biochemist Misher isolated from cell nuclei a hitherto unknown substance with the properties weak acid. Later, the chemist Levin found that the composition of this acid includes the carbohydrate deoxyribose, which is why it was called deoxyribonucleic acid (DNA). In 1920, the same Levin identified four nitrogenous bases in DNA: adenine (A), guanine (G), cytosine (C) and thymidine (T). Thus, already in the 20s of the XX century. scientists knew what DNA was made of. This information was significantly supplemented in 1950 by the biochemist Chargaf, who discovered that in the DNA molecule the amount of A is equal to the amount of T, and the amount of G is equal to the amount of C.
However, regarding the role of DNA in storage and transmission hereditary information, then for a long time there were only guesses about this. In 1944, the microbiologists Avery, McCarthy and McLeod for the first time transferred certain properties from one microbe to another using DNA.
And on February 28, 1953, two young scientists from the University of Cambridge, James Watson and Francis Crick, announced their discovery of the structure of the DNA molecule. They found that this molecule is a helix consisting of two chains. Each chain, which has a phosphate-sugar backbone, contains nitrogenous bases. Hydrogen bonds between A and T, on the one hand, and G and C, on the other, determine the stability of the double-helix structure. Watson and Crick determined that the sequence of nitrogenous bases in the structure of double-stranded DNA is the "code" genetic information, which is transmitted when copying (doubling) the molecule. When two strands of DNA are separated, new nucleotides can be attached to them, and a new one is formed near each of the old strands, exactly corresponding to it (since the combination of nucleotides A - T, G - C is the only possible one).
An article by Watson and Crick entitled "The Molecular Structure of Nucleic Acids" was published on April 25, 1953 in the journal Nature. In the same issue, an article was published by London scientists R. Franklin and M. Wilkins, which described the results of an X-ray study of a DNA molecule, which showed that this molecule is indeed a double helix.
The discovery of Watson and Crick was recognized almost all over the world (only the USSR was late, where genetics was defeated thanks to the efforts of Academician Lysenko). Already in 1961, the American biologists Nirenberg and Ochoa established that individual sections of DNA encode, i.e., determine the structure of completely specific protein structures (“three adjacent nucleotides encode one specific amino acid”). These scientists identified the codons corresponding to each of the 20 amino acids.
Naturally, the discovery of Watson and Crick provided only a basis for subsequent research, but without this basis, genetics probably could not develop further. In 1962, both scientists received the Nobel Prize.
In the first half of the 1970s, hybrid DNA molecules (“DNA-DNA”) were obtained for the first time, capable of penetrating into cells of various origins and stimulating the synthesis of proteins unusual for these cells. This was the birth of a new discipline - genetic engineering, which was immediately brought under government control due to its potential use in the creation of biological weapons. In 1977, the first version of the “machine” method for determining nucleotide sequences in a DNA molecule was developed, which dramatically increased the number of uncovered (“read”) genomic regions and entire genes. In 1982, the first therapeutic agent of a new generation, genetically engineered insulin, was obtained. It is produced by bacterial cells into which DNA encoding the protein structure of insulin is introduced. In 1983, a method was developed to increase the number of DNA molecules using the polymerase enzyme, and in 1985, a method of individual molecular “fingerprinting” (that is, a kind of “fingerprinting”) of each original DNA sample was developed. This made it possible to compare different DNA samples with each other to determine their identity or, on the contrary, dissimilarity. These methods immediately began to be used in forensic medicine to identify biological "traces of the crime", as well as to establish paternity. New genetic engineering technology for the production of certain foods is expanding. In 2000, the human genome was almost completely deciphered. Science has come close to the possibility of predetermining the phenotype, abilities, pathologies of a person who is just about to be born. And not only to determine, but also to correct, replace "diseased genes" with "healthy ones".
From the history of the discovery of the structure of DNA
In 1910, it became clear that genes are located on chromosomes. But it was not clear what material genes are made of - protein or nucleic acid.
In 1928, F. Griffith began to study the role of nucleic acids in cell life in experiments on pneumococci.
There are two types of pneumococci. One couple bacterial cells surrounded by a capsule. The second type of cells is without a capsule. The capsule protects microbes from phagocytosis. If you introduce such mice, they die. Pneumococcus without a capsule does not infect mice and does not cause pneumonia.
Experience. Mice were infected with a mixture of cells from live pneumococci without capsules and dead pneumococci with capsules.
The mice were expected to remain healthy. But they died of pneumonia. Live bacteria isolated from mice had capsules. This is the phenomenon of cell transformation.
Experience. Microbiologists have speculated that some substance in dead pneumococci can cause living cells to form capsules. They showed it in experiments.
Pneumococci with capsules were killed, crushed, and a solution was prepared from the destroyed cells - this is an extract. An extract from dead cells with capsules was added to the culture medium, then live pneumococci without capsules were added to this medium.
Result: some of the cells without capsules transformed into cells with capsules; their descendants also possessed capsules and, when administered to mice, caused pneumonia.
It turned out that cells without capsules underwent a change - they began to have capsules and caused pneumonia. It is important that their descendants also formed capsules and caused pneumonia.
Conclusion: 1) the signs of pneumococci have changed, 2) this is caused rather by the fact that some component of the extract or it has become part of the pneumococcus.
F. Griffith's experiments were continued by American scientists - microbiologist
FROM. Avery (1877-1955) and his staff.
They wondered: what substance causes the transformation of one strain of pneumococcus into another? To do this, they repeated the experiments of F. Griffith, using an extract from them instead of microbes.
The extract in experiments with pneumococci retained its transforming activity when proteins and RNA were destroyed in it, but lost it when DNA was destroyed.
Conclusion: the transforming substance is DNA. Hence genes are built from DNA.
Transformation consists in the transfer of genes from dead pneumococci to living ones and their introduction into the host chromosome, i.e. into capsular pneumococci.
The role of DNA in the cell has been supplemented from the life of viruses containing DNA. They infect bacterial cells in order to carry out the reproduction cycle in them.
At the same time, the ability of the DNA of the virus to synthesize its copies and proteins was discovered.
It follows from everything that DNA controls the life of the cells containing it and is able to synthesize copies of its molecules. This process is called "self-doubling" or reproduction. DNA is the only molecule in nature that can replicate.
Academician's contribution N.K. Koltsova
In 1927, our scientist - acad. N.K. Koltsov (1872-1940) wrote that "one incredibly long molecule fits in one chromosome, and separate groups of atoms - genes - are located along it."
He also said for the first time that “during cell division, such molecules are not created anew from separate pieces, but first complete the exact copies on themselves, and then the original molecule and the copy will disperse together with the daughter chromosomes into newly formed cells.” This is the matrix principle of replicating genes and then chromosomes before a cell divides into two.
How DNA is duplicated before cell division has been a mystery to biologists for decades. Scientists guessed that in order to understand this, it was necessary to know: 1) the structure of DNA and 2) the ways in which nucleotides are arranged in a molecule.
By 1950, it was known that DNA is a molecule, which consists of thousands of molecules interconnected in a line of four different types- nucleotides.
E. Chargaff (1950) showed that in any DNA the amount of adenine is equal to the amount of thymine (A=T), and the amount of guanine is equal to the amount of cytosine (G=C). This indicated that in the DNA molecule they are in pairs: A-T; G-Ts.
R. Franklin (1920-1958) in the laboratory of M. Wilkins obtained by X-ray crystallography "the now famous image of the picture of the structure of DNA."
However, from this knowledge it was not clear: how does this molecule work or what does it look like? No one knew how chemical units line up - A, T, G, C, in order to carry information about the plan of the structure and reproduction of living things.
DNA molecule model
D. Watson and F. Crick began to create a model of the DNA molecule, like L. Pauling - to study the spatial structure of the protein. It would help to understand the details of the structure and possible functions of DNA.
After doing the calculations, they were busy creating a model for 18 months and created a DNA model. But they were not sure about the correctness of this model.
Head R. Franklin - M. Wilkins allowed D. Watson to get acquainted with the X-ray image of the DNA molecule, without saying anything about it to R. Franklin. When D. Watson saw the image received by R. Franklin, he realized: "he and F. Crick were not mistaken." In this picture, they clearly saw signs spirals and immediately went to the laboratory to check "everything on a three-dimensional model."
Due to the lack of plates, D. Watson cut out four types of nucleotide models from cardboard: adenine (A), Thymine (T), guanine (G) and cytosine (C) and began to lay them out on the table.
He immediately discovered that adenine combines with thymine, and guanine with cytosine according to the “key-lock” principle, forming pairs. This is how the two strands of the DNA molecule are held together.
The sequence of these pairs in a molecule can vary infinitely. This serves as a cipher or code that encrypts information that determines the type of protein synthesized by a given cell (Fig. 1).
Rice. one.
Bases connected hydrogen bonds.
The DNA molecule has two functions: 1) to transmit information to offspring, i.e. daughter cells and 2) to realize the information inside the cell.
From the structure of the double helix, one can immediately see direct consequence– replication, i.e. reproduction of DNA. Method: the divergence of two complementary chains and the construction of a new, complementary chain for each of them. So from one DNA molecule, two are formed, which is required for cell division into two. Errors during replication, i.e. mutations are the reason for the transformation of a normal cell into a defective one (Fig. 2 and 3).
So, the matrix principle of DNA replication before division was proved
Cells, predicted by the great scientist, acad. N.K. Koltsov. Two parts of the molecule are separated from each other, and a new half of the molecule is synthesized from each of them. The order of the bases is in the role of a matrix or a model for completing the molecules.
DNA is the repository of genetic information
Information about the synthesis of each type of protein is embedded in DNA in the form of a certain linear sequence of bases.
In 1961, F. Crick proved that each group of three bases forms a codon. One codon codes for one amino acid of the 20 major amino acids.
To transfer information about the structure of the protein from the cell nucleus, there is mRNA. It is a copy from a fragment of the coding template DNA strand. It contains uracil instead of thymine.
According to mRNA in the ribosome with the help of transfer RNA, a protein will be synthesized - the final link in the implementation of genetic information. Since DNA serves as a repository of genetic information, it is called the molecule of life.
Before the work of D. Watson and F. Crick on the structure of DNA, much was already known.
R. Franklin in 1951 for the first time obtained the first unique X-ray diffraction pattern of the DNA molecule, which shows that this molecule has the shape of a double helix, very similar to a spiral staircase. Her photographs played a decisive role in the discovery of D. Watson and F. Crick. As a sign of this, R. Franklin is called the "pioneer" of molecular biology.
D. Watson, F. Crick and M. Wilkins were awarded the Nobel Prize in 1962 for the discovery of the structure of DNA and its functions. R. Franklin did not live. She died of cancer in 1958.
Revolution in the world of science
The discovery of the spatial structure of DNA became the basis for a number of new discoveries.
In the 60s. 20th century The mechanism of DNA replication was confirmed, an enzyme was found - DNA polymerase, which catalyzes this process.
The genetic code has been discovered, i.e. code for how proteins are synthesized in the cell.
In the 70s. 20th century two more methods were created: sequencing and obtaining recombinant DNA.
Obtaining recombinant DNA or molecular cloning method. The essence of this method is to insert a fragment containing a specific gene into a DNA molecule.
For example, they introduce it into a bacterium, and it synthesizes its product - a protein that a person needs.
In the 80s. 20th century developed polymerase chain reaction(PCR). This technology is necessary for the rapid "propagation" of the desired DNA fragment.
Using PCR, it is possible to carry out early diagnosis of bacterial and viral infections, as well as the first cancer cells in the patient's body by their marker genes.
For example, fragments of cancer cell marker genes can be detected in the patient's blood plasma. If the fragment is in a small amount or the only one, it is propagated using PCR and then easily identified.
The discovery of the structure of DNA enabled scientists to decipher the genome of humans and many other organisms. This discovery made it possible to move on to gene therapy for any disease, including cancer.
The cancer cell is "poorly recognized by the patient's immune system, because it arises from a normal host cell.”
Therefore, in order to destroy cancer cells with the help of gene therapy, it is necessary first to make cancer cells "foreign" for the immune system.
There are many ways to do this. It is possible to isolate cancer cells from the material of a cancer biopsy, introduce a "foreign" gene into them, and then introduce these cancer cells back into the patient's body. In this case, the immune system by the protein of this gene will recognize cancer cells as “foreign” and destroy them.
In experiments on animals, this method of influencing the DNA of cancer cells gave encouraging positive results. But for the treatment of cancer patients, a similar method is still at the stage of clinical trials.
(E.D. Sverdlov, 2003).
To the era of "live technologies"
And quite unusually - the beginning of a new era of "live technologies". Scientists in a number of countries say they are almost ready to create "artificial life", i.e. abiogenesis.
While there is no single definition of the living, it is characterized by three features; 1) the presence of a container, i.e. membrane containing the contents of the cell;
2) metabolism - the ability to convert basic nutrients in the working mechanisms of the cell; 3) the presence of genes - chemical structures necessary for building a cell, which can be transmitted to offspring and change along with changes in the environment.
Each of these three elements has already been reproduced in laboratories, scientists are ready to start trying to combine all this “into one working unit”, i.e. cell.
If successful, it will be "a world of ultra-small living machines: special cells will heal the human body and fight pollutants." environment substances."
Scientists consider the creation of an "artificial cell" capable of self-reproduction and producing unique chemical substances, including drugs that have not yet been synthesized.
"Artificial life" will be under the complete control of man, for example, "feeding" it with elements that are not found in nature in its pure form.
Synthesis of viruses and the beginning of cell synthesis
1. Prof. E. Wimmer (E. Wimmer) and his group from New York in 2002 for the first time since the birth of "living" on Earth, created the polio virus from non-living matter.
Scientists argue: are viruses living beings or inanimate objects?
MIND. Stanley, a Nobel laureate, believes that “in the cell, the virus behaves like a living being, but outside the cell it is as dead as a stone.”
G. Nadson, our microbiologist, says this: “A virus is either a substance that has the properties of a creature, or a creature with the properties of a substance.”
Acad. V.A. Engelhardt, our scientist, wrote: “Many viruses consist of only protein and nucleic acid. They can be attributed to chemical compounds - nucleoproteins.
The genome of the polio virus has been completely deciphered. On this basis, scientists have collected the exact sequence of nucleotides corresponding to a natural sample.
This genetic material was placed in a solution similar to cytoplasm. In it, according to the information embedded in DNA, the necessary proteins were synthesized.
Prof. E. Wimmer reports that as soon as all the genetic components were placed in the test tube, the virus immediately “self-assembled”. In other words,
"life, or at least its semblance, started up half a turn."
The created virus looked just like its natural sample. To prove the activity of the virus, scientists infected mice with it. The animals died with classic symptoms of polio.
On the assembly of the genome of the poliomyelitis virus prof. It took E. Wimmer three years.
In the same laboratory, J. Craig Venter synthesized the virus in 14 days.
2. Synthesis of artificial virus phi-X174. This bacteriophage exists in nature, safe for humans and animals.
K. Venter and his team took several sections of DNA and connected them, creating a complete genome of the virus, containing eleven genes. This mixture was placed in a test tube, where it self-assembled into a genetic chain identical to the phi-X174 genome. After that, the assembled genome was implanted into a living cell, which began to produce copies of the virus.
3. American scientists will create a form of life unknown in nature. Scientists from the Rockville laboratory announced their intention to create with the help of genetic engineering new form life - 21.11.2002.
The purpose of the project is to study the fundamental mechanisms of the origin and development of organic life. The main participants are the geneticist K. Venter and Nobel Laureate H. Smith.
The purpose of the experiment is to create a single cell, which is the base for the formation of an organism with a minimum set of genes to sustain life.
If the experiment is successful, then the grown cell will grow and divide, thus creating a whole cellular structure that does not exist in nature. It will be a "minimalist" organism.
In the late 1990s of the XX century. K. Venter - at that time the head of the Institute for Genomic Research in Rockville (USA), - published a list of genes necessary for the existence unicellular organism, are mycoplasmas. According to his calculations, this inhabitant of the human genital tract can get by with 300 of its 517 genes, which in this microbe form one chromosome.
The project is based on the same bacterium for 3 years. Scientists intend to extract all the genetic material from her cell, then assemble an artificial chain of genes from its “pieces”, i.e. chromosome. It will include only those bacterial genes that are “absolutely necessary” to maintain the life of a new organism. At the final stage, the assembled chain of genes will be incorporated into a cell devoid of genetic material.
Then “the most interesting thing should happen, that for which the experiment was conceived” - the revival of the bacterium. Next will be observations of such a semi-natural organism: how it lives and reproduces.
“We are interested in whether it is possible to arrive at a molecular definition of life, and our main goal is a fundamental understanding of the constituents of the most elementary living cell.”
In order to avoid the creation of a pathogenic agent, K. Venter and H. Smith will deprive the new “mycoplasma” of the genes responsible for its attachment to cells in the human body, then those genes that allow it to survive in adverse conditions. The result is "a rather fragile creature, absolutely dependent on its creators."
The task of research is also to learn how to artificially create various genes. “This is truly basic science,” says K. Venter. - Even
While we have discovered all the genes in the human genome, we still have not been able to figure out the mystery of the simplest cell. That is what we want to do now.”
K. Venter and H. Smith and their groups have another option for creating a living cell: artificially synthesize these basic genes in the laboratory, assemble them in a chain, and then introduce them into the same bacterium, from which all its genetic material will be preliminarily removed.
What does K. Venter put into his task - to give a "molecular definition of life"?
Any cell is built of molecules, like the body as a whole. Their structure and composition, as well as interaction, are laid down in the genes. In the process of evolution, each molecule is tailored to its function in the cell. A cell is not a chaotic accumulation of molecules, but "their orderliness", i.e. organization, since it is built by genes through products - proteins. Destroy it, although these cell molecules will remain in the form of a mixture, it will already be dead, since it is destroyed molecular organization cells. And it was created in the process of evolution of "living".
Hence: K. Venter strives with a minimum of genes to obtain such an organization of non-living molecules, which will turn into "living". This will be abiogenesis.
MOSCOW, April 25 - RIA Novosti, Tatyana Pichugina. Exactly 65 years ago, British scientists James Watson and Francis Crick published an article on deciphering the structure of DNA, laying the foundations of a new science - molecular biology. This discovery changed a lot in the life of mankind. RIA Novosti talks about the properties of the DNA molecule and why it is so important.
In the second half of the 19th century, biology was a very young science. Scientists were just beginning to study the cell, and the concept of heredity, although already formulated by Gregor Mendel, was not widely accepted.
In the spring of 1868, a young Swiss doctor, Friedrich Miescher, came to the University of Tübingen (Germany) to study scientific work. He intended to find out what substances the cell consists of. For experiments, I chose leukocytes, which are easy to obtain from pus.
Separating the nucleus from protoplasm, proteins and fats, Misher discovered a compound with a high content of phosphorus. He called this molecule nuclein ("nucleus" in Latin - nucleus).
This compound exhibited acidic properties, hence the term " nucleic acid". Its prefix "deoxyribo" means that the molecule contains H-groups and sugars. Then it turned out that it was actually a salt, but they did not change the name.
At the beginning of the 20th century, scientists already knew that nuclein is a polymer (that is, a very long, flexible molecule of repeating units), the units are composed of four nitrogenous bases (adenine, thymine, guanine and cytosine), and nuclein is contained in chromosomes - compact structures that occur in dividing cells. Their ability to transmit hereditary traits was demonstrated by the American geneticist Thomas Morgan in experiments on Drosophila.
The model that explained genes
But what deoxyribonucleic acid, abbreviated DNA, does in the cell nucleus, was not understood for a long time. It was believed that it plays some structural role in the chromosomes. The units of heredity - genes - were attributed to the protein nature. The breakthrough was made by American researcher Oswald Avery, who experimentally proved that genetic material is transmitted from bacterium to bacterium through DNA.
It became clear that DNA needed to be studied. But how? At that time, only X-rays were available to scientists. To shine through biological molecules, they had to be crystallized, which is difficult. Deciphering the structure of protein molecules from X-ray patterns was carried out at the Cavendish Laboratory (Cambridge, UK). Young researchers working there, James Watson and Francis Crick, did not have their own experimental data on DNA, so they used x-rays of colleagues at King's College Maurice Wilkins and Rosalind Franklin.
Watson and Crick proposed a model of the structure of DNA that exactly matches X-ray patterns: two parallel strands are twisted into a right-handed helix. Each chain is made up of an arbitrary set of nitrogenous bases strung on a backbone of their sugars and phosphates, and held together by hydrogen bonds stretched between the bases. Moreover, adenine combines only with thymine, and guanine with cytosine. This rule is called the principle of complementarity.
The Watson and Crick model explained the four main functions of DNA: the replication of genetic material, its specificity, the storage of information in a molecule, and its ability to mutate.
The scientists published their discovery in the journal Nature on April 25, 1953. Ten years later, together with Maurice Wilkins, they were awarded the Nobel Prize in Biology (Rosalind Franklin died in 1958 from cancer at the age of 37).
"Now, more than half a century later, it can be stated that the discovery of the structure of DNA played the same role in the development of biology as in physics - the discovery atomic nucleus. The elucidation of the structure of the atom led to the birth of a new, quantum physics, and the discovery of the structure of DNA led to the birth of a new, molecular biology,” writes Maxim Frank-Kamenetsky, an outstanding geneticist, DNA researcher, author of the book “The Most Important Molecule”.
Genetic code
Now it remained to find out how this molecule works. DNA was known to contain instructions for the synthesis of cellular proteins that do all the work in the cell. Proteins are polymers made up of repeating sets (sequences) of amino acids. Moreover, there are only twenty amino acids. Animal species differ from each other in the set of proteins in the cells, that is, in different sequences of amino acids. Genetics argued that these sequences are set by genes, which, as it was then believed, serve as the first building blocks of life. But what genes are, no one really knew.
Clarity was made by the author of the theory big bang physicist Georgy Gamov, employee of George Washington University (USA). Based on Watson and Crick's double-stranded DNA helix model, he suggested that a gene is a section of DNA, that is, a certain sequence of links - nucleotides. Since each nucleotide is one of the four nitrogenous bases, it's just a matter of finding out how four elements code for twenty. This was the idea behind the genetic code.
By the early 1960s, it was established that proteins are synthesized from amino acids in ribosomes - a kind of "factory" inside the cell. To start protein synthesis, an enzyme approaches DNA, recognizes a certain area at the beginning of the gene, synthesizes a copy of the gene in the form of a small RNA (it is called matrix), then a protein is grown from amino acids in the ribosome.
They also found out that the genetic code is three-letter. This means that three nucleotides correspond to one amino acid. The unit of code is called a codon. In the ribosome, information from mRNA is read codon by codon, sequentially. And each of them corresponds to several amino acids. What does the cipher look like?
This question was answered by Marshall Nirenberg and Heinrich Mattei from the USA. In 1961, they first reported their results at a biochemical congress in Moscow. By 1967, the genetic code had been completely deciphered. It turned out to be universal for all cells of all organisms, which had far-reaching consequences for science.
The discovery of the structure of DNA and the genetic code has completely reoriented biological research. The fact that each individual has a unique DNA sequence has dramatically changed forensic science. The deciphering of the human genome has given anthropologists a whole new way to study the evolution of our species. The recently invented CRISPR-Cas DNA editor has greatly advanced genetic engineering. Apparently, this molecule contains the solution to the most pressing problems of mankind: cancer, genetic diseases, aging.
V. Ivanov, Doctor of Physical and Mathematical Sciences
Sixty years ago a remarkable thing was done scientific discovery. On April 25, 1953, an article was published on how the most mysterious molecule, the deoxyribonucleic acid molecule, works. It is called DNA for short. This molecule is found in all living cells of all living organisms. Scientists discovered it more than a hundred years ago. But then no one knew how this molecule is arranged and what role it plays in the life of living beings.
The English physicist Francis Crick and the American biologist James Watson managed to finally solve the mystery. Their discovery was very important. And not only for biologists, who finally found out how the molecule works, which controls all the properties of a living organism. One of the largest discoveries of mankind was made in such a way that it is absolutely impossible to say what science this discovery belongs to - chemistry, physics and biology are so closely merged in it. This fusion of sciences is the most striking feature of the discovery of Crick and Watson.
ONE MOLECULE CAN BE LOOKED DIFFERENTLY
Scientists have long been interested in the secret of the main property of all living organisms - reproduction. Why do children - whether we are talking about people, bears, viruses - look like their parents, grandparents? In order to discover the secret, biologists have examined a variety of organisms.
And scientists have found that special particles of a living cell - chromosomes - are responsible for the similarity of children and parents. They are like small sticks. Small sections of the rod-chromosome are called genes. There are a lot of genes, and each is responsible for some sign of the future organism. If we talk about a person, then one gene determines the color of the eyes, the other determines the shape of the nose ... But what the gene consists of and how it works, scientists did not know this. True, it was already known: chromosomes contain DNA and DNA has something to do with genes.
Different scientists wanted to unravel the mystery of the gene: each looked at this mystery from the point of view of his science. But in order to find out how a gene, a small particle of DNA, is arranged, it was necessary to find out how the molecule itself is arranged and what it consists of.
Chemists who research chemical composition substances, studied the chemical composition of the DNA molecule. Physicists began to scan DNA with X-rays, as they usually do with crystals, to find out how these crystals are arranged. And they found out that DNA is like a helix.
Biologists were interested in the mystery of the gene, of course, more than anyone else. And Watson decided to tackle the problem of the gene. In order to learn from advanced biochemists and learn more about the nature of the gene, he traveled from America to Europe.
At that time, Watson and Crick did not yet know each other. Watson, after working for some time in Europe, made no significant progress in elucidating the nature of the gene.
But on one of scientific conferences he learned that physicists study the structure of the DNA molecule using their own physical methods. Upon learning this, Watson realized that physicists would help him discover the secret of the gene, and went to England, where he got a job in a physical laboratory in which biological molecules were studied. It was here that Watson and Crick met.
HOW THE PHYSICIST KRICK GOT INTERESTED IN BIOLOGY
Crick had no interest in biology at all. Until he came across a book by the famous physicist Schrödinger "What is life from the point of view of physics?".
In this book, the author suggested that the chromosome is like a crystal. Schrödinger noticed that the "reproduction" of genes resembles the growth of a crystal, and suggested that scientists consider a gene a crystal. This proposal interested Crick and other physicists. That's why.
A crystal is a very simple physical body in structure: the same group of atoms repeats in it all the time. And the device of the gene was considered very complicated, since there are so many of them and they are all different. If genes are made up of the substance of DNA, and the DNA molecule is arranged in the same way as a crystal, then it turns out that it is both complex and simple. How so? Watson and Crick realized that physicists and biologists knew too little about the DNA molecule. True, something was known about DNA to chemists.
HOW WATSON HELPED THE CHEMISTS AND THE CHEMISTS HELPED THE SCREAM
Chemists knew that the DNA molecule contained four chemical compounds: adenine, thymine, guanine, and cytosine. They were designated by the first letters - A, T, G, C. Moreover, there was as much adenine as thymine, and guanine as much as cytosine. Why? Chemists could not understand this.
They guessed: it had something to do with the structure of the molecule. But how, they did not know. The biologist Watson helped the chemists.
Watson was accustomed to the fact that in wildlife many things occur in pairs: a pair of eyes, a pair of arms, a pair of legs, there are, for example, two sexes: male and female ... It seemed to him that a DNA molecule could also consist of two chains. But if DNA is like a helix, as X-ray physicists have found out, then how do two strands in this helix hold each other? Watson suggested that with the help of A, G, C and T, which, like hands, are stretched out to each other. Having cut out the contours of these chemical compounds, Watson applied them this way and that for a long time, until he suddenly saw: adenine combines perfectly with thymine, and guanine with cytosine.
Watson told Crick about it. He quickly figured out how the double helix should actually look - in space, and not in the picture.
Both scientists began to build a model of DNA.
How is it to "build"? That's how. From a molecular constructor that resembles a children's toy constructor. In the molecular designer, the parts are balls-atoms, which are fastened to each other with buttons in the order in which the atoms are located in the substance. 
The molecular designer was invented by another scientist, the chemist Pauling. He built models of protein molecules and found out that they must have sections that look like spirals. Very soon this was confirmed by the physicists of the laboratory where Crick worked. An important biological problem was solved theoretically.
Crick liked Pauling's method so much that he suggested that Watson build a model of DNA using a molecular constructor. This is how the model of the famous DNA Double Helix was created, which you can see in the picture.
And what is remarkable: due to the fact that A in one chain can only "stick together" with T in another, and G - only with C, the "chemical" rule is automatically fulfilled, according to which the amount of A is equal to the amount of T, and the amount of G is the number of Cs. But the most important thing is that, looking at the Double Helix of DNA, it is immediately clear how to solve the riddle of gene reproduction. It is enough to "unwind" the DNA pigtail, and each chain will be able to complete a new one on itself so that A sticks together with T, and G - with C: there was one gene - there are two. Due to the fact that the dimensions steam A-T and G-C are the same, the DNA molecule actually resembles a crystal in structure, as physicists assumed.
And at the same time, this "crystal" can contain a variety of combinations of A, T, C, G, and therefore all genes are different.
The solution of the gene problem by Watson and Crick led to the fact that literally in 2–3 years a whole new area of natural science was formed, which was called molecular biology. Often it is called physico-chemical biology.
HOW "PHYSICISTS" AND "LYRICS" STOP ARGUING
Other examples of mutual penetration of different sciences into each other can be cited. Mathematics, for example, is widely used in astronomy, physics, and even in ... linguistics, the science of the structure of language.
Mathematical Methods, for example, allow you to identify the true author of unknown manuscripts. We found an unknown poem in the archives, and who is its author? Scientists suggest that the famous poet wrote. But how can this assumption be tested? Mathematicians count how many times a certain word occurs in this work, or, say, in what sequence words occur in a text. The same calculations are made in famous work alleged author. The results are compared. If they match, then the original manuscript has been found. This is how mathematicians return to us, the readers, the works of famous writers and poets stolen by time.
Or, for example, physics and music... What can an exact science have in common with art? It turns out there is something in common.
On stringed instruments - violin, cello - the musician himself chooses the desired pitch. The violinist does not like how, for example, the note “do” sounds, it seems to him that it should sound a little higher or, on the contrary, a little lower - he himself will select the exact sound on the string. The pianist cannot do this. On the keyboard, each key is a specific note. No matter how many times you press it, it will sound the same. This means that for the exact performance of a piece of music, the piano must be very precisely tuned. Physicists have calculated the frequency of sound oscillations, according to which musical keyboard instruments can be tuned most accurately. As you can see, it would be difficult for musicians and linguists without physicists and mathematicians.
Modern man you need to have a wide variety of knowledge. This is especially important for today's scientist. In our time, many compound sciences have appeared: physical chemistry and chemical physics, even, as you now know, physico-chemical biology. What does all this have to do with you? The most direct.
At school, I didn’t even think that someday I would study biology. I was more interested in exact sciences. And now I'm doing biology.
Wrong to divide school items the ones you need and the ones you don't. Who knows what might come in handy later?
In 1952, the English biophysicist Rosalind Franklin discovered that deoxyribonucleic acid (DNA) resembles a spiral staircase in its structure. However, the glory of this discovery, which laid the foundation for modern research genes, subsequently assigned to Maurice I Wilkins, as well as Francis Crick and James Watson.
The structure of heredity I Rosalind Franklin proceeded from the assumption that DNA of enormous length - a polymer molecule of nucleotides - must consist of repeating blocks. To test this hypothesis, the English researcher could not simply resort to a microscope. Such submicroscopic phenomena can only be captured by X-ray diffraction. Therefore, the researcher exposed DNA molecules to X-rays and, as a result of long, painstaking work, found that their structure is a double helix. So for the first time it was possible to imagine the structure of the main component of human life.
A discovery left in the shadows
Franklin did not immediately publish the results of her study. She wanted first to get confirmation of her observations from her colleagues. In 1953, Maurice Wilkins, Franklin's manager, without her knowledge, gave the results provided to him to his collaborator Crick and the biochemist Watson. By that time, these scientists already knew the chemical composition of DNA: sugar, deoxyribose, phosphate, and the nitrogen-containing bases adenine, cytosine, guanine, and thymine, and they instantly appreciated the significance of Franklin's data.
The Nobel Prize is not awarded posthumously.
Crick and Watson, having made some additions and changes to the work, published it under proper names. The famous article "The molecular structure of nucleic acids: the structure of deoxyribonucleic acid", which appeared in the journal Nature in 1954, aroused great enthusiasm in the scientific world. Watson and Crick created a logically invulnerable model that became the basis for further research. Meanwhile, Rosalind Franklin died in 1958 of cancer at the age of 37. Nobel Prize in Medicine for the discovery of the structure of DNA was awarded in 1962 to Crick, Watson and Wilkins.
- 1865: Gregor Johann Medel established the laws of inheritance of genetic principles.
- 1970: Hamilton O. Smith and Daniel Nathane laid the foundations of genetic engineering.
- 1973: The first genetically modified bacterium is created in the United States.
- 1976: Indian biophysicist Har Gobind Korana synthesizes the first complete gene.
