About DNA! !

DNADNA (abbreviation of English deoxyribonucleic acid), also known as deoxyribonucleic acid, is the main chemical component of chromosomes and is also composed of genes, sometimes called "genetic particles". DNA is a molecule that can form genetic instructions to guide biological development and life function. Its main function is long-term information storage, which can be compared to "blueprint" or "menu". The instructions contained therein require the construction of other compounds in cells, such as protein and RNA. DNA fragments with genetic information are called genes and other DNA sequences, some of which directly work with their own structures, while others participate in regulating the expression of genetic information.

Monomer deoxyribonucleic acid-polymer of deoxyribonucleic acid chain, also known as DNA. In the process of reproduction, parents copy a part of their DNA (usually half, that is, one of the DNA double strands) to their offspring, thus completing the spread of traits. Therefore, the chemical substance DNA will be called "genetic particle". Eukaryotic cell is a long DNA molecule. There are more than one chromosome in the nucleus of eukaryotic cells, and each chromosome contains one or two pieces of DNA. However, they are usually larger than DNA molecules in prokaryotic cells and bind to protein. The function of DNA molecules is to store all the genetic information of almost all protein and RNA molecules that determine species traits; Code and design all the procedures of orderly transcription of genes and expression of protein by biological organisms in a certain time and space, and complete directional development; The unique character and personality of the organism and all the stress reactions when interacting with the environment are preliminarily determined. In addition to chromosomal DNA, there are very few DNA with different structures in mitochondria and chloroplasts of eukaryotic cells. The genetic material of DNA virus is also DNA, and a few are RNA.

DNA is a long-chain polymer, its constituent unit is called nucleotide, and sugar and phosphoric acid molecules are connected through ester bonds to form its long-chain skeleton. Each sugar molecule is connected with one of the four bases, and the sequence formed by these bases arranged along the long chain of DNA can form a genetic code, which is the basis of protein's amino acid sequence synthesis. The process of reading the password is called transcription, which is to copy a nucleic acid molecule called RNA according to the DNA sequence. Most RNA carries the information of synthesizing protein, while others have their own special functions, such as rRNA, snRNA and siRNA.

Quadruplex DNA

When simulating the telomere DNA of 1 protozoan Echinococcus, Sundpuist and Klug synthesized the 1 DNA sequence artificially, and found that the simulated G-rich single-stranded DNA could form a quadruplex DNA structure under certain conditions. It is speculated that quadruplexes are also formed between single strands at the telomere tail of chromosomes. Kang et al. confirmed through experiments that G-rich DNA can also form quadruplex DNA structure in crystals and solutions respectively.

The basic structural unit of quadruplex DNA is G- quadruplex, that is, 1 pocket surrounded by four negatively charged carboxyl oxygen atoms in the center of quadruplex, and intramolecular or intermolecular dextral helices can be formed through the accumulation of G- quadruplex. Compared with DNA double helix structure, G- quadruplex helix has two remarkable characteristics: 1, and its stability depends on the cations bound in the pocket. 2. Its thermodynamic and kinetic properties are very stable.

Based on the analysis of DNA sequences of some organisms, it is known that most of the DNA sequences rich in guanine exist in some genome regions which are quite conservative in function and evolution. Many studies have shown that G-DNA, which is formed by guanine-rich DNA chains, may be one of the elements recognized by molecules and play some special roles in organism cells.

dna replication

DNA is the carrier of genetic information, so the parent DNA must be accurately copied into two parts with its own molecule as a template and distributed to two daughter cells in order to complete its mission of genetic information carrier. The double-stranded structure of DNA is very important for maintaining the stability and accuracy of this kind of genetic material.

Semi-conservative replication of DNA

Waston and Click studied the process of DNA replication when they proposed the model of DNA double helix structure. It was found that the hydrogen bond between bases was first broken (by helicase), the double helix structure was unwound and separated, and each chain was used as a template to synthesize new chains. Because one strand of each progeny DNA comes from the parent and the other strand is newly synthesized, it is called semi-conservative replication.

(2) DNA replication process

1.unwinding of DNA double helix

(1) single-stranded DNA binding protein (SSB DNA protein).

(2)DNA helicase

(3)DNA melting

2. Okazaki fragment and semi-discontinuous replication

3. Initiation and termination of replication

(3) Telomere and telomerase

194 1 year, the American Indian Mc Clintock put forward the telomere hypothesis, and thought that there must be a special structure at the end of chromosome-telomere. At present, it is known that chromosome telomeres have at least two functions: ① to protect chromosome ends from damage and maintain chromosome stability; ② It is connected with the nuclear fiber layer, so that the chromosome can be located.

[Edit this paragraph] Physical and chemical properties of ]DNA

DNA is a polymer, and DNA solution is a high viscosity polymer solution. DNA can absorb ultraviolet rays, and when nucleic acid denatures, the absorption value increases. After renaturation of denatured nucleic acid, the absorbance value will return to the original level. Temperature, organic solvents, pH, urea, amide and other reagents can all cause DNA molecular denaturation, even if the hydrogen bond between DNA double bonds breaks and the double helix structure is unbound.

DNA (deoxyribonucleic acid) refers to the polymer of deoxyribonucleic acid (a component of chromosomes and genes) and is the main component of chromosomes. Most genetic information is stored in DNA molecules.

[Edit this paragraph] Enzymatic catalytic activity of ]DNA

In the 1990s, Cuenoud and others discovered that DNA also has enzymatic activity. They designed and synthesized a single-stranded DNA composed of 47 nucleotides according to the sequence of * * *, which can catalyze the connection between two substrate DNA fragments. The bifunctional nature of DNA challenges the evolutionary view of "RNA world".

[Edit this paragraph] Distribution and function

The chromosome of prokaryotic cell is a long DNA molecule. There are more than one chromosome in the nucleus of eukaryotic cells, and each chromosome contains only one DNA molecule. However, they are usually larger than DNA molecules in prokaryotic cells and bind to protein. The function of DNA molecule is to store all the genetic information that determines the structure of protein and RNA. Planning the time and space for organisms to synthesize cells and tissue components in an orderly manner; It determines the activities of the organism from beginning to end in the life cycle and determines the personality of the organism. In addition to chromosomal DNA, there are very few DNA with different structures in mitochondria and chloroplasts of eukaryotic cells. The genetic material of DNA virus is also DNA.

The discovery of DNA

Since Mendel's genetic law was rediscovered, people have raised another question: Are genetic factors material entities? In order to solve the problem of what genes are, people began to study nucleic acids and protein.

Mendel, the founder of genetics, discovered nucleic acid as early as 1868. In the laboratory of German chemist Hope Sailor, there is a Swiss graduate student named Michel (1844- 1895). He is very interested in the bandages with purulent blood thrown by a hospital near the laboratory, because he knows that purulent blood is the "remains" of white blood cells and human cells that died in the "battle" with germs in order to protect human health. So he carefully collected the purulent blood on the bandage and decomposed it with pepsin. As a result, he found that most of the cell debris was decomposed, but it had no effect on the nucleus. He further analyzed the substances in the nucleus and found that the nucleus contained a substance rich in phosphorus and nitrogen. Hope Sailor experimented with yeast, which proved that Michelle found the substance in the nucleus correct. So he named this substance separated from the nucleus "nuclide", and later found that it was acidic, so it was renamed "nucleic acid". Since then, people have carried out a series of fruitful research on nucleic acid.

At the beginning of the 20th century, the German pirate ship (1853- 1927) and his two students, Jones (1865- 1935) and Levin (1869-1. Nucleotides are composed of bases, ribose and phosphoric acid. There are four kinds of bases (adenine, guanine, thymine and cytosine) and two kinds of ribose (ribose and deoxyribose), so nucleic acids are divided into ribonucleic acid (RNA) and deoxyribonucleic acid (DNA).

Levin, who was eager to publish his own research results, mistakenly thought that the amount of four bases in nucleic acid was equal, and thus deduced that the basic structure of nucleic acid was four nucleotides connected by four different bases, which were polymerized into nucleic acid, and put forward the "four-nucleotide hypothesis". This false assumption greatly hinders the understanding of complex nucleic acid structure, and also affects people's understanding of nucleic acid function to some extent. It is believed that although nucleic acid exists in an important structure-the nucleus, its structure is too simple to imagine what role it can play in the genetic process.

American geneticist Morgan protein discovered nucleic acid 30 years earlier and developed rapidly. In the 20th century, 12 of the 20 amino acids that make up protein have been discovered, and all of them were discovered by 1940.

1902, the German chemist Fischer put forward the theory that amino acids are linked by peptide chains to form protein. 19 17 years, he synthesized a 18 peptide chain consisting of 15 glycines and 3 leucines. Therefore, some scientists think that protein may play a major role in heredity. If heredity involves nucleic acid, it must be a nucleoprotein linked with protein. So at that time, the biological community generally tended to think that protein was the carrier of genetic information.

1928, American scientist Griffith (1877- 194 1) experimented on mice with a highly toxic pneumococcus with an envelope and an attenuated pneumococcus without an envelope. He killed pod bacteria with high temperature and injected them into human mice with live bacteria without pods. As a result, he found that the mouse soon became ill and died, and at the same time, he isolated live pod bacteria from the blood of the mouse. This shows that Agabi actually got something from the dead Agabi and turned Agabi into Agabi. Is this assumption correct? Griffith did another experiment in the test tube, and found that when dead bacteria and living bacteria without pods were cultured in the test tube at the same time, all bacteria without pods became pods, and found that it was the residual nucleic acid in the shell of dead bacteria with pods that made bacteria without pods grow protein pods (because the nucleic acid in pods was not destroyed during heating). Griffith called nucleic acids "transforming factors".

1944, American bacteriologist Avery (1877- 1955) isolated an active "transforming factor" from American bacteria, made a test to check the existence of protein, and the result was negative, which proved that the "transforming factor" was DNA. However, this discovery has not been widely recognized. People suspect that the technology at that time could not remove protein, and the residual protein played a role in transformation.

The phage group of German-American scientist delbruck (1906- 198 1) firmly believes Avery's discovery. Because they observed the morphology of phage and the growth process of entering Escherichia coli under electron microscope. Phage is a virus that takes bacterial cells as its host. It is so small that it can only be seen with an electron microscope. It is like a tadpole, with a head membrane and a tail sheath composed of protein. The head contains DNA, and the tail sheath has tail silk, substrate and small hook. When phage infects Escherichia coli, the tail end is first tied to the bacterial cell membrane, and then all the DNA inside is injected into the bacterial cell. Protein's empty shell is left outside the bacterial cells, which has no effect. After phage DNA enters bacterial cells, phage DNA and protein are rapidly synthesized by using substances in bacteria, thus many new phages with the same size and shape as the original ones are replicated. It was not until the bacteria completely disintegrated that these phages left the dead bacteria and infected other bacteria.

1952, Hershey (1908 I), the main member of phage group, and his student Chase used advanced isotope labeling technology to do the experiment of phage infecting Escherichia coli. He labeled the nucleic acid of E.coli T2 phage with 32P and the protein shell with 35S. Escherichia coli was infected with T2 phage, and then it was isolated. Results Phage left an empty shell with 35S label outside E.coli, only the nucleic acid with 32P label inside the phage was injected into E.coli, and the phage successfully propagated in E.coli.. This experiment proves that DNA has the function of transmitting genetic information, and protein is synthesized by the instructions of DNA. This result was immediately accepted by the academic community.

Almost at the same time, Austrian biochemist Chagav (1905-) re-determined the content of four bases in nucleic acid, and achieved results. Under the influence of Avery's work, he thinks that if different biological species are due to different DNA, then the structure of DNA must be very complicated, otherwise it will be difficult to adapt to the diversity of the biological world. Therefore, he doubted Levin's "Tetranucleotide Hypothesis". During the four years of 1948- 1952, he used paper chromatography which was more accurate than that of Levin's time, separated the four bases and made quantitative analysis by ultraviolet absorption spectrum. After repeated experiments, he finally got a different result from Levin. The experimental results show that the total number of purines and pyrimidines in DNA macromolecules is equal, among which the number of adenine A and thymine T is equal, and the number of guanine G and cytosine C is equal. It shows that the bases A and T, G and C in DNA molecules exist in pairs, thus denying the "tetranucleotide hypothesis" and providing important clues and basis for exploring the molecular structure of DNA.

1On April 25th, 953, the British magazine Nature published the research results of Watson and Crick in Cambridge University: the molecular model of DNA double helix structure, which was later hailed as the greatest discovery of biology since the 20th century, marking the birth of molecular biology.

Watson (1928 I) was an extremely clever boy in middle school. He entered the University of Chicago at the age of 15. At that time, because of an experimental education plan that allowed early study, Watson had the opportunity to study the biological science course in all aspects. During his college years, Watson had little formal training in genetics, but since reading Schrodinger's What is Life? -the physical appearance of living cells ",prompted him to" discover the secret of genes ". He is good at brainstorming, learning from others and enriching himself with other people's ideas. As long as there are convenient conditions, you can get the knowledge you need without forcing yourself to learn the whole new field. Watson received his doctorate at the age of 22 and was sent to Europe for postdoctoral research. In order to fully understand the chemical structure of a virus gene, he went to the laboratory in Copenhagen, Denmark to study chemistry. Once he and his tutor attended a biomacromolecule conference in Naples, Italy, and had the opportunity to listen to a lecture by British physical biologist Wilkins (19 16-), and saw the DNAX-ray diffraction photos of Wilkins. Since then, the idea of finding the key to unlock the DNA structure has been retrieved in Watson's mind. Where can I learn to analyze X-ray diffraction patterns? So he went to the Cavendish laboratory of Cambridge University in England to study, during which Watson met Crick.

Crick (19 16-2004) was enthusiastic about science when he was in middle school, and 1937 graduated from London University. In 1946, what does he read about life? -the physical appearance of living cells, determined to apply physical knowledge to the study of biology, and became interested in biology from then on. 1947, repeat graduate student. 1949, he and Peruz used X-ray technology to study the molecular structure of protein, so they met Watson here. At that time, Crick was older than Watson 12 years old, and had not yet obtained his doctorate. But they talked very speculatively, and Watson felt lucky to find someone here who knew that DNA was more important than protein. At the same time, Watson thinks Crick is the smartest person he has ever met. They talk for at least a few hours every day to discuss academic issues. Two people complement each other, criticize each other and inspire each other. They believe that solving the molecular structure of DNA is the key to solving the genetic mystery. Only with accurate X-ray diffraction data can we find out the structure of DNA more quickly. In order to get the data of DNAX-ray diffraction, Crick invited Wilkins to Cambridge for the weekend. In the conversation, Wilkins accepted the view that DNA structure is spiral, and also talked about his collaborator Franklin (1920- 1958, female) and the scientists in the laboratory, who were also thinking hard about the problem of DNA structure model. From 195 1 year1month to1April, 9531August, Watson and Crick had several important academic exchanges with Wilkins and Franklin.

195 1 year1month, Watson was deeply inspired after listening to Franklin's detailed report on DNA structure. Watson and Crick, who have a certain understanding of crystal structure analysis, realize that if they want to build a DNA structure model quickly, they can only use other people's analysis data. They quickly put forward the idea of triple helix DNA structure. 195 1 At the end, they invited Wilkins and Franklin to discuss this model. Franklin pointed out that they underestimated the water content of DNA by half, so the first model failed.

One day, Watson went to Wilkins Laboratory at King's College, and Wilkins took out a recent X-ray diffraction photograph of "B-type" DNA taken by Franklin. Watson immediately got excited when he saw the photo, and his heart beat faster, because this image was much simpler than the previous "A type". Just look at the "B-type" X-ray diffraction photos and simply calculate, you can determine the number of polynucleotide chains in DNA molecules.

Crick asked a mathematician to help him calculate, and the results showed that Yuanyin had a tendency to attract pyrimidine. According to this result and the result that two purines and two pyrimidines of nucleic acid obtained from Chagaff are equal to each other, they formed the concept of base pairing.

They think hard about the sequence of four bases, draw the base structure on paper again and again, fiddle with the model, put forward assumptions again and again, and overthrow their own assumptions again and again.

Watson (left) and Crick Watson once again fiddled with the model according to their own ideas. He moved bases to look for various pairing possibilities. Suddenly, he found that a thymine pair connected by two hydrogen bonds had the same shape as a cytosine pair connected by three hydrogen bonds, so his spirit was greatly uplifted. Because the mystery of why the number of songs of purine is exactly the same as that of pyrimidine is about to be solved. Chagaff's law suddenly became the inevitable result of DNA double helix structure. Therefore, it is not difficult to imagine how to use one strand as a template to synthesize another strand with complementary base sequences. Then, the skeletons of the two chains must be in opposite directions.

After intense and continuous work by Watson and Crick, the DNA metal model was quickly assembled. From this model, we can see that DNA is composed of two nucleotide chains, which are intertwined in opposite directions along the central axis, much like a spiral staircase. The armrests on both sides are the skeleton of alternating combination of sugar and phosphorus genes of two polynucleotide chains, and the pedals are base pairs. Due to the lack of accurate X-ray data, they dare not conclude that this model is completely correct.

Wilkins

Franklin's next scientific method is to carefully compare the diffraction pattern predicted by this model with the experimental data of X-ray. They called Wilkins again. In less than two days, Wilkins and Franklin confirmed the correctness of the double helix structure model with X-ray data analysis, and wrote two experimental reports, which were published in the British journal Nature. 1962, Watson, Crick and Wilkins won the Nobel Prize in Medicine and Physiology, while Franklin died of cancer in 1958, and did not win the prize.

In the late 1930s, Swedish scientists proved that DNA was asymmetric. After World War II, the diameter of DNA molecule measured by electron microscope was about 2 nm.

After the discovery of DNA double helix structure, it greatly shocked the academic circles and inspired people's thoughts. Since then, people have immediately carried out a lot of molecular biology research centered on genetics. Firstly, an experimental study was carried out on how to arrange and combine four bases to encode and express 20 amino acids. 1967, the genetic code was completely cracked, and the gene got a new concept at the molecular level of DNA. It shows that gene is actually a fragment of DNA macromolecule, and it is the functional unit and structural unit of genetic material that controls biological traits. Many nucleotides in this unit fragment are not randomly arranged, but arranged in a meaningful password order. A certain structure of DNA can control the synthesis of protein of the corresponding structure. Protein is an important component of organisms, and the characteristics of organisms are mainly reflected by protein. Therefore, the control of genes on traits is realized by DNA controlling the synthesis of protein. On this basis, genetic engineering, enzyme engineering, fermentation engineering, protein engineering and so on have appeared one after another. The development of these biotechnology will surely make people use biological laws to benefit mankind. With the development of modern biology, it is becoming more and more obvious that it will become a leading discipline.

Development of DNA recombination technology

In 1950s, the double helix structure of DNA was clarified, which opened a new chapter in life science and initiated a new era of science and technology. Subsequently, the molecular mechanism of heredity-DNA replication, genetic code, the central rule of genetic information transmission, gene as the basic unit of heredity and the blueprint of cell engineering, and the regulation of gene expression have been recognized one after another. At this point, people have fully realized that DNA and its genes are the things that control the fate of all living things. The difference between biological evolution process and life process is caused by the different trajectories of DNA and genes.

Knowing the great role and value of DNA, life scientists first thought of whether it is possible to break the iron law of natural inheritance in some aspects closely related to human interests, so as to make patients' genes turn from evil to right to achieve the purpose of treating diseases and "graft" gene fragments from different sources to produce new varieties and new qualities ... So, an attractive scientific fantasy miraculously became a reality. This happened in the early 1970s.

The scientific and technological means to realize this scientific miracle is DNA recombination technology. 1972, American scientist Paul? Berg successfully recombined the first batch of DNA molecules in the world for the first time, which indicates that the DNA recombination technology-genetic engineering, as the foundation of modern bioengineering, has become the foundation and core of modern biotechnology and life science.

The specific content of DNA recombination technology is to recombine DNA fragments containing a specific gene from different sources by artificial means, so as to change the biological gene type and obtain a specific gene product.

In the middle and late 1970s, due to the emergence of engineering bacteria and the engineering nature of DNA recombination and post-processing, genetic engineering or genetic engineering was widely used as a synonym for DNA recombination technology. Now, genetic engineering also includes genome modification, nucleic acid sequence analysis, molecular evolution analysis, molecular immunology, gene cloning, gene diagnosis and gene therapy. It can be said that the fruitful achievements of DNA recombination technology in the past 30 years have brought people into an incredible and fantastic scientific world, giving them the golden key to unlock the mysteries of life and prevent and treat diseases.

At present, the achievements of DNA recombination technology are various. By the end of the 20th century, the biggest application field of DNA recombination technology was in the medical field, including the production of active peptides, protein and vaccines, the pathogenesis, diagnosis and treatment of diseases, the isolation of new genes and environmental monitoring and purification.

Many active peptides and protein have the functions of treating and preventing diseases, and they are all produced by corresponding genes. However, because the yield in tissues and cells is extremely small, it is difficult to obtain enough yield for clinical application by conventional methods.

Genetic engineering has broken through this limitation, and this kind of polypeptide and protein can be produced in large quantities. Up to now, more than 65,438+000 products have been successfully produced, such as insulin for treating diabetes and schizophrenia, interferon for treating hematological tumors and some solid tumors, human growth hormone for treating dwarfism, and growth hormone release inhibitors for treating acromegaly and acute pancreatitis.

Genetic engineering can also introduce antigen-related DNA into living microorganisms, so that they can grow in the host after immune stress to produce attenuated live vaccine, which has the advantages of large dose and long duration of antigen stimulation. At present, there are dozens of genetically engineered vaccines under development, including vaccines against leprosy, whooping cough, gonococcus and meningococcus. There are vaccines against hepatitis A, hepatitis B, cytomegalovirus, herpes simplex, influenza and human immunodeficiency virus. There are as many as 120 million hepatitis B virus carriers and patients in China, which prompted China scientists to independently develop hepatitis B vaccine and achieved great social and economic benefits.

Antibody is one of the main weapons for human immune system to prevent and treat diseases. Although the monoclonal antibody technology founded in 1970s has played an important role in the prevention and treatment of diseases, its clinical application is limited because it is difficult to obtain human monoclonal antibodies. In order to solve this problem, in recent years, scientists have obtained human antibodies by using DNA recombination technology, which can not only ensure their specificity and affinity for antigen binding, but also ensure their normal function. At present, a variety of such antibodies have been clinically tested. For example, humanized anti-HER-2 monoclonal antibody has entered the third phase of breast cancer trial, and humanized anti-IGE monoclonal antibody has entered the second phase of asthma trial.

Antibiotics play an important role in the treatment of diseases. With the increase of the number of antibiotics, the probability of finding new antibiotics by traditional methods is getting lower and lower. In order to obtain more new antibiotics, DNA recombination technology has become one of the important means. At present, people have obtained dozens of genetically engineered "hybrid" antibiotics, which has opened up a new therapeutic approach for clinical application.

It is worth pointing out that the genetic engineering peptide, protein, vaccine, antibiotics and other preventive and therapeutic drugs are not only effective in controlling diseases, but also superior to similar drugs produced by traditional methods in avoiding toxic and side effects, so they are more favored by people.

Human diseases are directly or indirectly related to genes. Diagnosing and treating diseases at the gene level can not only achieve the accuracy and originality of etiological diagnosis, but also make the diagnosis and treatment specific, sensitive, simple and rapid. Diagnosis and treatment at the gene level are professionally called gene diagnosis and gene therapy. At present, as the fourth generation clinical diagnosis technology, gene diagnosis has been widely used in the diagnosis of genetic diseases, tumors, cardiovascular and cerebrovascular diseases, viral and bacterial parasitic diseases and occupational diseases. The goal of gene therapy is to create gene recombinants with specific functions through DNA recombination technology to compensate the functions of genes that have lost their functions, or to add some functions to help correct or eliminate abnormal cells.

Theoretically, gene therapy is a radical method without any side effects. However, although there are more than 100 gene therapy schemes in clinical trials, there are still some theoretical and technical difficulties in gene therapy, which still makes this treatment method far from being widely used. Whether it is to determine the genetic cause, implement gene diagnosis, gene therapy, or study the pathogenesis of diseases, the key prerequisite is to understand the genes related to specific diseases. With the completion of the "Human Genome Project", scientists will fully understand all human genes, which creates conditions for using gene recombination technology to force human health.

However, although genetic technology has shown its wonderful "magician" charm to human beings, a large number of scientists have expressed great concern about the impact of the development of this technology on human ethics and the natural laws of ecological evolution. Theoretically, one extreme of the development of this technology is to enable human beings to create any life form or creature that has never existed before. Can people imagine what the result will be?

Scientists have found new codes in DNA besides genetic codes.

According to media reports in Taiwan Province Province, American and Israeli scientists believe that they have found a second code in DNA besides the genetic code. The newly discovered password is responsible for determining the position of the nuclear body, that is, the miniature protein axis surrounding DNA. These spools simultaneously protect and control access to the DNA itself.

This discovery, if confirmed, may open up new knowledge about the mechanism of controlling higher genes. For example, every kind of human cell can activate the genes it needs, but it can't touch the genes used by other kinds of cells. This is a key and mysterious process.

In this issue of Nature, seguer of Weizmann Institute, Wilton of Northwestern University and their colleagues described this new DNA code.

There are about 30 million nucleosomes in each human cell. The reason why so many nucleosomes are needed is that DNA strands cover each nucleosome only 165 times, each DNA helix contains 147 units, and the length of DNA molecules in a single chromosome may be as high as 225 million units.

Biologists have suspected for many years that some positions on DNA, especially those positions where DNA is most easily bent, may be more conducive to the existence of nucleosomes than others, but the overall pattern is not obvious. Now, Dr. seguer and Dr. Wheaton have analyzed the sequence of about 200 positions in the yeast gene, where nucleosomes are known to interweave with each other, and they found that there are indeed hidden patterns.

By understanding this model, they successfully predicted the location of about 50 nucleation bodies in other organisms. This pattern is a combination of two sequences, which can make DNA easier to bend and tightly wrap checker. However, in this model, the entanglement position of each nucleus only needs several sequences, so it is not obvious. Because of its loose formation conditions, it does not conflict with the genetic code.