structure of DNA

DNA is composed of many deoxynucleotidyl residues with each other by a certain order of 3 ', 5'-phosphate ester bond linked to a long chain. Most of DNA containing two such long-chain, and some DNA for single-chain, such as E. coli phage φ X174, G4, M13, and so on. Some DNA for the ring, some for the linear DNA. Mainly with adenine, guanine, thymine and cytosine four kinds of bases. In some types of DNA, 5 - cytosine-to a certain extent can replace the CD, wheat germ DNA of 5 - methyl cytosine particularly rich, up 6 percent Moore. In some phage, 5 - hydroxymethyl cytosine replaced the CD. The late 1940s, Chargaff (E. Chargaff) found that different species of DNA base pairs of different, but the number of adenine equivalent to the number of its thymine (A = T), guanine cytosine equal to the number of (G = C), and thus the number of purine equivalent to the number of and pyrimidine. General painted with several levels of DNA structure. A structure of DNA in a structure that is its base sequence. Gene is a fragment of DNA, the genetic information stored in its genetic sequence of. 1975 U.S. Gilbert (W. Gilbert) and the United Kingdom Sanger (F. Sanger) respectively, created the structure of DNA a rapid determination of their total for the year 1980 Nobel Prize in Chemistry. Since then, determination and constantly improved, many of the DNA structure of an established. If people ring of mitochondrial DNA contains 16,569 base pairs, λ phage containing 48,502 DNA base pairs, rice chloroplast genome of 134,525 base pairs, tobacco chloroplast genome of 155,844 base pairs, and so on. Now the U.S. has plans to 10-15 years in all human DNA molecule of about 3 billion nucleotide pairs out of sequence. Secondary structure in 1953, Watson (Watson) and Crick (Crick) to the basic structure of DNA fibers is the double helix structure, but this model, the scientists acknowledged, and to explain reproduction, transcription and other important life process. After in-depth study and found that because of humidity and the base sequence of different conditions, DNA double helix can have many types, mainly divided into A, B and Z three categories. Is generally believed that, B configuration of the nearest cell in the DNA conformation, it is the double helix model is very similar. A-DNA and RNA molecules in the double helix, as well as the formation of transcription, DNA-RNA hybrid molecular conformation close. Z-DNA nucleotide dimer as a unit to the left to the winding, its main chain was serrated (Z) form, Gu Ming. This configuration of the chain for more than purine nucleotide pyrimidine alternate area. 1989, U.S. scientists used scanning tunneling electron microscope method to directly observe the DNA double helix DNA double helix: in 1952, Austria-American biochemists Chargaff (E.chargaff, 1905 -) of the DNA base pairs in the four kinds of Content found gland fat methotrexate and equal to the number of thymine, cytosine bird fat methotrexate and the number of the same. This makes Watson, Crick immediately think of four kinds of bases exists between the corresponding relations between February 2 and formed a gland fat methotrexate and thymine pairs, the birds fat methotrexate cytosine pairs with the concept

DNA is the carrier of genetic information

DNA is the carrier of genetic information, the parent must take their own DNA molecule as a template accurate reproduction into two copies, and assigned to the two daughter cells, go to complete its mission of the carrier of genetic information. And the double-stranded DNA structure of this type of genetic material for the maintenance of the stability and the accuracy of reproduction are extremely important. (A) DNA copy of the semi-reservation Click Waston and raised in the DNA double helix structure on the model of DNA replication during the process of the study, they speculate, DNA base pairs in the process of copying the hydrogen bonds between the first fracture, double helix of the Rotary separately, were linked to each template Synthesis of the new chain, each offspring of a DNA chain from the pro-generation, and the other is a new synthesis, so as to retain a half-copy (semiconservative replication). (B) DNA replication 1. DNA double helix of the rotation (1) single chain DNA-binding protein (single-stranded DNA binding protein, ssbDNA protein) (2) DNA helicase (DNA helicase) (3) DNA of the chain 2. Okazaki fragments and a half does not copy a row 3. Copy the trigger and termination (C) telomeres and telomerase 1941-American Indians McClintock (Mc Clintock) raised a telomere (telomere) of the hypothesis that the chromosome ends must exist a special structure - the telomere. Telomere now known at least two roles: ① chromosome end protection from damage to chromosomes remained stable; ② and nuclear fiber-connected so that the chromosome can be targeted. [DNA of the physical and chemical properties -- [Edit this paragraph] DNA is macromolecular polymers, DNA solution for the polymer solution, with very high viscosity. DNA on the role of ultraviolet radiation is absorbed, when the nucleic acid degeneration, the absorption value increased when the degeneration of the nucleic acid can be complex, absorption values will be restored to the original level. Temperature, organic solvents, acidity, urea, amide, and other reagents DNA molecules can cause degeneration, even in the DNA double bond between the hydrogen bond breaking double helix structure untied. DNA (deoxyribonucleic acid) that DNA (genes and chromosomes an integral part of) deoxynucleotidyl the polymer, is the major components of chromosomes. The vast majority of genetic information stored in the DNA molecule. [Distribution and function -- [Edit this paragraph] Prokaryotic cell chromosome is a long DNA molecule. Eukaryotic cells in more than one chromosome, each chromosome containing only a DNA molecule. But their general than the original cells in the DNA molecule and protein and the combination. DNA molecule's function is the storage of all species decision RNA structure of the protein and all the genetic information; orderly planning of cells and tissue components of the time and space; identified throughout the life cycle of biological activity and identify biological personality. In addition to chromosomal DNA, a very small amount of the different structure of DNA found in eukaryotic cells in the mitochondria and chloroplasts. DNA of the virus genetic material is DNA. [The discovery of DNA -- [Edit this paragraph] Since the genetic Mendel's law was re-discovered, the people also raised a question: genetic factor is not a material entity » In order to solve the problem of what is, people began to DNA and protein research. As early as 1868, people have discovered DNA. German chemist in the laboratory Huopei Siler, a Swiss post-graduate名叫米歇尔(1844 - 1895), his lab near a hospital threw the bandage with a sense of Nongxue Interest, because he knows that those Nongxue to defend human health, germs and "combat" and died in the WBC and was killed in human cells, "body." So he carefully the bandage on the Nongxue collected and used pepsin decomposition, and found the bodies of most of the cell decomposition, but the nuclear non-functional. He further material within the nucleus of an analysis and found that cells containing a phosphorus and nitrogen-rich material. Huopei Siler experiments with yeast, that the nucleus Michel substances found to be correct. So he would give such a separation from the nucleus of the material named "nuclide", and later it was discovered that it was acidic, so to call "DNA." From then on the people of nucleic acid carried out a series of fruitful research. The early 20th century, Germany Ke Saier (1853 - 1927) and two of his students Jones (1865 - 1935) and Levin (1869 - 1940) study, understand the basic chemical structure of nucleic acid, that it Nucleotide is composed of many macromolecules. Nucleotide base pairs from, ribose and phosphate posed. Of which there are four kinds of bases (gland Piao Yin, the birds allopurinol-Yin, thymine and cytosine), there are two ribose (ribose, deoxyribose), the DNA into RNA (RNA) and deoxyribonucleic acid (DNA) . Levin eager to present his research results, the misconception that four kinds of bases in DNA, are equivalent to the volume, which is derived from the basic structure of DNA by four with different nucleotide base pairs of connecting the four-nucleoside Acid, as the basis for a nucleic acid polymer, proposed a "four nucleotide hypothesis." This hypothesis wrong, the understanding of the complex structure of nucleic acids from the considerable obstacles, also, to a certain extent, affected the people's understanding of the function of DNA. It was felt that although the DNA structure exists in the important - the nucleus, but its structure is too simple, it is difficult to envisage it in the process of genetic what role. Protein than the discovery of DNA as early as 30, have developed rapidly. The beginning of the 20th century, composed of 20 kinds of protein has 12 kinds of amino acids were found to 1940, all were found. 1902, a German chemist for Xie Erti between amino acid peptide chain connected to the formation of protein theory, in 1917 he was synthesized by the glycine 15 leucine and three of the 18 components of long-chain peptide . Thus, some scientists envisaged, it's likely that the genetic protein plays a major role. If the participation of genetic DNA, and protein is also bound together the nucleoprotein at work. Therefore, when biological protein is generally inclined to think that the carrier of genetic information. 1928, U.S. scientists Griffith (1877 - 1941) have used a capsule, and a toxic-free capsule, toxic weak Streptococcus pneumoniae experiments on rats. He used a high temperature to kill bacteria pod after pod with no live bacteria inject people with mice, rats and he soon found that the incidence death, and he's in the blood of rats from isolated the bacteria live in a pod. This shows that even without passing bacteria from the dead of a pod of what was in the material, so that no dioxin into a pod of bacteria. This assumption is correct? » Griffith also in the test tube experiments and found to have died in the U.S. with live bacteria without passing on the bacteria at the same time in test-tube culture, without passing all of a pod into a bacteria, and found that no pod of long Protein to dioxins is dead in a pod of shell left over from the nucleic acid (as in the heating, dioxin in the nucleic acid has not been damaged). Griffith said the DNA for "transforming factor." 1944, the United States Xijunxuejia Avery (1877 - 1955) from the United States have isolated the activity of the "conversion factor", and this kind of material to the test whether there is the protein test results were negative, and proved "Conversion factor" is the DNA. However, this discovery has not been widely recognized, people suspected of technology at that time can not be a net addition of protein, a protein residue into the role. American scientists德尔布吕克Germany (1906 - 1981) of the phage group firmly believe that the discovery of Avery inalienable. Because they are under the electron microscope to observe the shape of the phage into E. coli and the growth process. Phage bacterial cell is a host for the virus, individual and small, with only electron microscope to see it. It is like a small tadpole, the external is composed of protein from the first film and the tail sheath, the head of the internal containing DNA, on the tail end of silk sheath, the substrate and small hook. When the phage infection Escherichia coli, the first扎in the tail end of the cell membrane of bacteria, then it would inject all of the DNA in human cells to the bacteria, protein shell of bacteria cells remain on the outside, no longer what role the . After the bacteria enter the cells of the phage DNA, the use of bacterial material and rapid synthesis of DNA and protein phage, which many copy and the original shape of the same size phage new phage, until the bacteria was completely disintegrated, these phage did not leave the dead bacteria , Go the other bacterial infection. In 1952, key members of phage group Heer Xi (1908) and his students Chase isotope tag with advanced technology, do phage infection of the E. coli experiments. He E. coli T2 phage DNA markers on 32 P, protein shell markings on the 35 S. To use the T2 tag phage infection of the E. coli, and then be separated, the phage will be marked with 35 S shell to stay outside in E. coli, only within a 32 P phage DNA markers were all Note Escherichia coli, E. coli, and Phage the successful conduct of breeding. This experiment proved that a DNA transfer of genetic information, which is the protein from the DNA of the directive. This result was immediately accepted by the academic community. Almost at the same time, Austria biochemists Chargaff (1905 -) in the four kinds of nucleic acid bases in the re-determination have been fruitful. In Avery's work under the influence, he considered that if the different species is due to the different DNA, the DNA structure must be very complicated, or difficult to adapt to biological diversity. Therefore, he set out on the text of the "four nucleotide hypothesis" had a doubt.

DNA Correction

Gene therapy is integrated with the normal gene into the cells, to correction and replacement of a disease gene therapy. Currently in broad terms, some will be transferred to the genetic material of cells, in its role to achieve the objective method of treatment of disease, but also that of gene therapy. At present gene therapy, the method used can basically be divided into the following: 1  DNA Correction DNA correction that will be linked pathogenic DNA base pairs to correct the anomaly, and normal part be retained. 2. DNA replacement DNA replacement is to use the normal DNA in DNA by homologous recombination, in situ lesions replacement cells pathogen DNA, the DNA within the cell to fully return to normal conditions. 3. The addition of DNA DNA will be added to that purpose DNA into cells or other cell disease, removing abnormal DNA, but through DNA purpose of the non-targeting, the expression of compensation to the function of DNA defects or the original function has been strengthened. At present DNA for use of such methods. This approach is the addition of the more dominant DNA for the treatment of recessive disease. 4. DNA inactivation Early generally refers to anti-sense DNA technology. It is the specific anti-RNA, including antisense RNA, antisense and ribozymes DNA into cells, transcription and translation in blocking the abnormal expression of certain genes. In recent years another anti-gene strategy, peptide nucleic acid, DNA and RNA interference removal. [DNA is the genetic material of all biological basis: DNA (deoxyribonucleic acid) is a nucleic acid category, because of the presence of deoxyribose named. DNA molecules very large (at least in general molecular weight over 1 million), the main component is deoxynucleotidyl adenine, guanine deoxynucleotidyl, thymine and cytosine deoxynucleotidyl deoxynucleotidyl. DNA exists in the nucleus, mitochondria, chloroplasts, can also be free to exist in some state of the cell cytoplasm. Most of the known phage, part of a small number of plant and animal virus also contain the virus in the DNA. In addition to RNA (ribonucleic acid) and the phage, DNA is the genetic material of all biological basis. Parent-child organisms and the similarity between the so-called inheritance of genetic information, are stored in the DNA molecule. 1953,詹姆斯沃森and Francis Crick describe the structure of DNA: from one-to-many linked nucleotide composition of each other coiled double helix. They and London's National Institute of Technology physicist Frederick Ke Wei Er Jinsi shared the 1962 Nobel Prize in Physiology or Medicine. [Obesity gene -- The Royal London Hospital scientists found that obesity in the body, there is a unique function of the gene, the gene of the three members of the body of the chromosome. As the obesity gene existed only in the body, so scientists call it "fat gene." The study found that obesity gene can promote the body to create a transport fat in the blood protein - "APO-D" gene. The gene, the more fat the more fluent of blood transmission, the accumulation of body fat also the more people will be obese. Below scientists did an interesting experiment: Let a pair of carrying the obesity gene mice mating, the results of each roll and future generations of wandering round melon, which is tantamount to meat ball, and did not allow a mouse obesity gene for mating, birth The less fat in mice, each are very thin. Genetic scientists in accordance with this model, can also produce the body of fat at 20 to 50 percent of the Feishou different degrees of mice. Further found that the genetic obesity and the situation is slightly different from rodents, a generational genetic. That is, people can observe, in a considerable number of families, fat grandmother would not normally be obese gene passed on to their children, but passed on to her grandchildren. Scientists also found that obesity-related genes more than one. For example, New York, a Rockefeller University research team recently announced that they After eight years of long study, found that a control appetite and energy metabolism genes. It is said that this gene to the brain can send a signal to stop eating, so that the masters of the brain weakened appetite timely, in order to avoid excess energy if the gene variation, the owner will be increased appetite, Tanzui eat, and eventually become A big fat man. Further research revealed that the gene from the 4500 base component, part of which can produce from 167 amino acids of the protein. If this normal protein synthesis, will be sent to the brain's signal to stop eating if the protein coding the amino acid composition of coding the first 105 amino acid residues of the unusual base, the signal will stop eating failure, leading t

Gene therapy

Gene therapy is integrated with the normal gene into the cells, to correction and replacement of a disease gene therapy. Currently in broad terms, some will be transferred to the genetic material of cells, in its role to achieve the objective method of treatment of disease, but also that of gene therapy. At present gene therapy, the method used can basically be divided into the following: 1  DNA Correction DNA correction that will be linked pathogenic DNA base pairs to correct the anomaly, and normal part be retained. 2. DNA replacement DNA replacement is to use the normal DNA in DNA by homologous recombination, in situ lesions replacement cells pathogen DNA, the DNA within the cell to fully return to normal conditions. 3. The addition of DNA DNA will be added to that purpose DNA into cells or other cell disease, removing abnormal DNA, but through DNA purpose of the non-targeting, the expression of compensation to the function of DNA defects or the original function has been strengthened. At present DNA for use of such methods. This approach is the addition of the more dominant DNA for the treatment of recessive disease. 4. DNA inactivation Early generally refers to anti-sense DNA technology. It is the specific anti-RNA, including antisense RNA, antisense and ribozymes DNA into cells, transcription and translation in blocking the abnormal expression of certain genes. In recent years another anti-gene strategy, peptide nucleic acid, DNA and RNA interference removal. [DNA is the genetic material of all biological basis: DNA (deoxyribonucleic acid) is a nucleic acid category, because of the presence of deoxyribose named. DNA molecules very large (at least in general molecular weight over 1 million), the main component is deoxynucleotidyl adenine, guanine deoxynucleotidyl, thymine and cytosine deoxynucleotidyl deoxynucleotidyl. DNA exists in the nucleus, mitochondria, chloroplasts, can also be free to exist in some state of the cell cytoplasm. Most of the known phage, part of a small number of plant and animal virus also contain the virus in the DNA. In addition to RNA (ribonucleic acid) and the phage, DNA is the genetic material of all biological basis. Parent-child organisms and the similarity between the so-called inheritance of genetic information, are stored in the DNA molecule. 1953,詹姆斯沃森and Francis Crick describe the structure of DNA: from one-to-many linked nucleotide composition of each other coiled double helix. They and London's National Institute of Technology physicist Frederick Ke Wei Er Jinsi shared the 1962 Nobel Prize in Physiology or Medicine. [Obesity gene -- The Royal London Hospital scientists found that obesity in the body, there is a unique function of the gene, the gene of the three members of the body of the chromosome. As the obesity gene existed only in the body, so scientists call it "fat gene." The study found that obesity gene can promote the body to create a transport fat in the blood protein - "APO-D" gene. The gene, the more fat the more fluent of blood transmission, the accumulation of body fat also the more people will be obese. Below scientists did an interesting experiment: Let a pair of carrying the obesity gene mice mating, the results of each roll and future generations of wandering round melon, which is tantamount to meat ball, and did not allow a mouse obesity gene for mating, birth The less fat in mice, each are very thin. Genetic scientists in accordance with this model, can also produce the body of fat at 20 to 50 percent of the Feishou different degrees of mice. Further found that the genetic obesity and the situation is slightly different from rodents, a generational genetic. That is, people can observe, in a considerable number of families, fat grandmother would not normally be obese gene passed on to their children, but passed on to her grandchildren. Scientists also found that obesity-related genes more than one. For example, New York, a Rockefeller University research team recently announced that they After eight years of long study, found that a control appetite and energy metabolism genes. It is said that this gene to the brain can send a signal to stop eating, so that the masters of the brain weakened appetite timely, in order to avoid excess energy if the gene variation, the owner will be increased appetite, Tanzui eat, and eventually become A big fat man. Further research revealed that the gene from the 4500 base component, part of which can produce from 167 amino acids of the protein. If this normal protein synthesis, will be sent to the brain's signal to stop eating if the protein coding the amino acid composition of coding the first 105 amino acid residues of the unusual base, the signal will stop eating failure, leadi

discovered DNA

When the gene and found that the link between DNA, people still like to know how this DNA is a kind of things, it is also what specific approach to the lives of so many information to the new successor does » First of all people want to know what DNA is composed of human love is always asked at the end of this shaver. The results have a called Levin of scientists through research, found that DNA from four of the smaller things, these four things name is the total nucleotide, like four brothers, all of them named nucleotide, But names are different, are adenine (A), guanine (G), cytosine (C) and thymine (T), the four names to remember, but remember that as long as the DNA is from four Nucleotide only casually together, and they have no connection to each other laws, but later nucleotides in fact not the same, and their mutual combination of the ever-changing methods of great mystery. Now, people have basically learned about the genetic How did it happen. The 20th century biological research found that: the human body is composed of cells, cell by cell, composed of the nucleus and cytoplasm. Known in the nucleus of a substance called chromosomes, it is called by some major deoxyribonucleic acid (DNA) of the material composition. Of the genetic material exists in all cells, this kind of material called DNA. DNA from the nucleotide polymerization. And each nucleotide phosphate, ribose and a base. There are five bases, respectively, adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U). Each contains only the five nucleotide base pairs in one. Even a single nucleotide into a chain, linked by two nucleotide a certain order, and then twisted into a "Serratula" kind, a deoxyribonucleic acid (DNA) of the molecular structure. In this structure, every three bases can form a genetic "password" and a DNA base pairs on as many as several million, so each DNA is a significant genetic code books, the inside of the genetic information In countless more, this DNA molecule found in the nucleus on the chromosome. They will pass with cell division genetic code. The genetic traits from the password to pass. Probably have 25,000 genes, and each gene is determined by the password. The same gene in both parts have different parts. Different parts of the difference between people decided that human diversity. A total of 3 billion DNA genetic code, are composed of about 25,000 genes. [Structure] [Edit this paragraph] DNA is composed of many deoxynucleotidyl residues with each other by a certain order of 3 ', 5'-phosphate ester bond linked to a long chain. Most of DNA containing two such long-chain, and some DNA for single-chain, such as E. coli phage φ X174, G4, M13, and so on. Some DNA for the ring, some for the linear DNA. Mainly with adenine, guanine, thymine and cytosine four kinds of bases. In some types of DNA, 5 - cytosine-to a certain extent can replace the CD, wheat germ DNA of 5 - methyl cytosine particularly rich, up 6 percent Moore. In some phage, 5 - hydroxymethyl cytosine replaced the CD. The late 1940s, Chargaff (E. Chargaff) found that different species of DNA base pairs of different, but the number of adenine equivalent to the number of its thymine (A = T), guanine cytosine equal to the number of (G = C), and thus the number of purine equivalent to the number of and pyrimidine. General painted with several levels of DNA structure. A structure of DNA in a structure that is its base sequence. Gene is a fragment of DNA, the genetic information stored in its genetic sequence of. 1975 U.S. Gilbert (W. Gilbert) and the United Kingdom Sanger (F. Sanger) respectively, created the structure of DNA a rapid determination of their total for the year 1980 Nobel Prize in Chemistry. Since then, determination and constantly improved, many of the DNA structure of an established. If people ring of mitochondrial DNA contains 16,569 base pairs, λ phage containing 48,502 DNA base pairs, rice chloroplast genome of 134,525 base pairs, tobacco chloroplast genome of 155,844 base pairs, and so on. Now the U.S. has plans to 10-15 years in all human DNA molecule of about 3 billion nucleotide pairs out of sequence. Secondary structure in 1953, Watson (Watson) and Crick (Crick) to the basic structure of DNA fibers is the double helix structure, but this model, the scientists acknowledged, and to explain reproduction, transcription and other important life process. After in-depth study and found that because of humidity and the base sequence of different conditions, DNA double helix can have many types, mainly divided into A, B and Z three categories. Is generally believed that, B configuration of the nearest cell in the DNA conformation, it is the double helix model is very similar. A-DNA and RNA molecules in the double helix, as well as the formation of transcription, DNA-RNA hybrid molecular conformation close. Z-DNA nucleotide dimer as a unit to the left to the winding, its main chain was serrated (Z) form, Gu Ming. This configuration of the chain for more than purine nucleotide pyrimidine alternate area. 1989, U.S. scientists used scanning tunneling electron microscope method to directly observe the DNA double helix DNA double helix: in 1952, Austria-American biochemists Chargaff (E.chargaff, 1905 -) of the DNA base pairs in the four kinds of Content found gland fat methotrexate and equal to the number of thymine, cytosine bird fat methotrexate and the number of the same. This makes Watson, Crick immediately think of four kinds of bases exists between the corresponding relations between February 2 and formed a gland fat methotrexate and thymine pairs, the birds fat methotrexate cytosine pairs with the concept. DNA replication [Edit this paragraph] DNA is the carrier of genetic information, the parent must take their own DNA molecule as a template accurate reproduction into two copies, and assigned to the two daughter cells, go to complete its mission of the carrier of genetic information. And the double-stranded DNA structure of this type of genetic material for the maintenance of the stability and the accuracy of reproduction are extremely important. (A) DNA copy of the semi-reservation Click Waston and raised in the DNA double helix structure on the model of DNA replication during the process of the study, they speculate, DNA base pairs in the process of copying the hydrogen bonds between the first fracture, double helix of the Rotary separately, were linked to each template Synthesis of the new chain, each offspring of a DNA chain from the pro-generation, and the other is a new synthesis, so as to retain a half-copy (semiconservative replication). (B) DNA replication 1. DNA double helix of the rotation (1) single chain DNA-binding protein (single-stranded DNA binding protein, ssbDNA protein) (2) DNA helicase (DNA helicase) (3) DNA of the chain 2. Okazaki fragments and a half does not copy a row 3. Copy the trigger and termination (C) telomeres and telomerase 1941-American Indians McClintock (Mc Clintock) raised a telomere (telomere) of the hypothesis that the chromosome ends must exist a special structure - the telomere. Telomere now known at least two roles: ① chromosome end protection from damage to chromosomes remained stable; ② and nuclear fiber-connected so that the chromosome can be targeted. [DNA of the physical and chemical properties -- [Edit this paragraph] DNA is macromolecular polymers, DNA solution for the polymer solution, with very high viscosity. DNA on the role of ultraviolet radiation is absorbed, when the nucleic acid degeneration, the absorption value increased when the degeneration of the nucleic acid can be complex, absorption values will be restored to the original level. Temperature, organic solvents, acidity, urea, amide, and other reagents DNA molecules can cause degeneration, even in the DNA double bond between the hydrogen bond breaking double helix structure untied. DNA (deoxyribonucleic acid) that DNA (genes and chromosomes an integral part of) deoxynucleotidyl the polymer, is the major components of chromosomes. The vast majority of genetic information stored in the DNA molecule. [Distribution and function -- [Edit this paragraph] Prokaryotic cell chromosome is a long DNA molecule. Eukaryotic cells in more than one chromosome, each chromosome containing only a DNA molecule. But their general than the original cells in the DNA molecule and protein and the combination. DNA molecule's function is the storage of all species decision RNA structure of the protein and all the genetic information; orderly planning of cells and tissue components of the time and space; identified throughout the life cycle of biological activity and identify biological personality. In addition to chromosomal DNA, a very small amount of the different structure of DNA found in eukaryotic cells in the mitochondria and chloroplasts. DNA of the virus genetic material is DNA. [The discovery of DNA -- [Edit this paragraph] Since the genetic Mendel's law was re-discovered, the people also raised a question: genetic factor is not a material entity » In order to solve the problem of what is, people began to DNA and protein research. As early as 1868, people have discovered DNA. German chemist in the laboratory Huopei Siler, a Swiss post-graduate名叫米歇尔(1844 - 1895), his lab near a hospital threw the bandage with a sense of Nongxue Interest, because he knows that those Nongxue to defend human health, germs and "combat" and died in the WBC and was killed in human cells, "body." So he carefully the bandage on the Nongxue collected and used pepsin decomposition, and found the bodies of most of the cell decomposition, but the nuclear non-functional. He further material within the nucleus of an analysis and found that cells containing a phosphorus and nitrogen-rich material. Huopei Siler experiments with yeast, that the nucleus Michel substances found to be correct. So he would give such a separation from the nucleus of the material named "nuclide", and later it was discovered that it was acidic, so to call "DNA." From then on the people of nucleic acid carried out a series of fruitful research.

telomere gradual

British scientists discovered that telomere gradual depletion of the pathogenesis of heart disease may play a key role. They conducted a new study shows that often the author's heart telomere than healthy people much shorter. Telomere-end cell chromosome is the centromere. Human cells each split time, will be shortened telomeres, when the telomere short得不could short-term, you can not split the cells died. In the process of cell division, telomeres extent of the depletion vary from person to person. Elderly, children shorter than telomere length, it is because of the elderly after several separatist, more because of telomere attrition. According to "New Scientist" magazine reported that the British University of Leicester and Glasgow University researchers used five years of follow-up survey in 1542, aged 45 and 64 men between the ages of 5-year period 484 people suffering from heart disease . Comparative study found that people with shorter telomeres risk of heart disease is double the others. The study also found that the effectiveness of cholesterol-lowering statin drugs can reduce it seems that telomere attrition, not even the telomere degradation. Responsible for the study of Leicester University cardiologist Naier Shen Sa Mani said that his team has already begun laboratory studies, analysis of how these drugs have an effect on the telomere.

earthquake-stricken

Yesterday afternoon, including Hu Shengli, the backbone of the province's 50 forensic investigators and the build-up in Hangzhou. If there are no special circumstances, forensic today will be sent to the earthquake-stricken area to participate in disaster relief. To the disaster areas, in addition to rescue the injured, the forensic will mainly engage in individual identification of the victims, and to identify the unclaimed bodies of the victims, archive classified, and extract DNA samples from the victims, so that the pro-people Find casualties personnel information. 50 forensic ready-to Dongyang City Public Security Bureau, Hu Shengli is a forensic, good physique, rich work experience. After careful selection, the council decided to send him to the disaster areas in Sichuan disaster relief support. 17:00 yesterday, a reporter Hu Shengli phone calls. Hu Shengli said that they had just opened in Hangzhou End mobilization of the General Assembly, is still in its standby status. The province has assembled a 50 forensic, now in final preparations to receive the higher level once notified, immediately left for the earthquake-stricken area. Heard that the neighbouring Sichuan and Yunnan, Guizhou provinces such as forensic, has entered the disaster area to work. For the forthcoming to the destination, forensic who is not aware of, such as higher-level public security departments need to coordinate. "Each of the forensic team, have counterparts in the affected region. But no matter where assigned, we will do our best to complete the task." Hu Shengli said. 50 a day to deal with the remains After entering the disaster areas, will mainly engage in forensic identification of individual work. Records of the victims of the old features, the players kept their goods, for DNA extraction, for the future of information officers to find casualties, leaving the final file, reflects the respect for the deceased. To the implementation of the difficulty of this task, Hu Shengli said frankly that is still difficult to predict. "The first is not familiar with the environment in disaster areas, the earthquake occurred a few days, the situation certainly more complicated, but also to ease the mental stress, after all, to direct the face of so many victims." Hu Shengli said. Hu Shengli said that the disaster-Jin, the workload will be very large, many times more than usual. Judging from the current available information, a forensic daily average of nearly 50 to deal with the victims remains, but so many days have passed, and must be tested as soon as possible, the completion of individual identification, time is also very tight. Full support for pro-people Hu Shengli said that the daily news broadcast in the disaster areas any way, we all know, the aftershocks still occur from time to time, food, water also quite tense, dangerous certainly exist. "But my family went to the Sichuan disaster relief, are very supportive of. Disaster areas can do that, they feel glorious. In addition to biscuits, dry food, such as Su Bing, Hu Shengli's father last night also a group of night, a bag of speculation Meigan Cai, urged his son to put on. "In fact, they are very worried about my safety, but in the face of disaster, everyone has to small home care for everyone." Hu Sheng

gene

When the gene and found that the link between DNA, people still like to know how this DNA is a kind of things, it is also what specific approach to the lives of so many information to the new successor does » First of all people want to know what DNA is composed of human love is always asked at the end of this shaver. The results have a called Levin of scientists through research, found that DNA from four of the smaller things, these four things name is the total nucleotide, like four brothers, all of them named nucleotide, But names are different, are adenine (A), guanine (G), cytosine (C) and thymine (T), the four names to remember, but remember that as long as the DNA is from four Nucleotide only casually together, and they have no connection to each other laws, but later nucleotides in fact not the same, and their mutual combination of the ever-changing methods of great mystery. Now, people have basically learned about the genetic How did it happen. The 20th century biological research found that: the human body is composed of cells, cell by cell, composed of the nucleus and cytoplasm. Known in the nucleus of a substance called chromosomes, it is called by some major deoxyribonucleic acid (DNA) of the material composition. Of the genetic material exists in all cells, this kind of material called DNA. DNA from the nucleotide polymerization. And each nucleotide phosphate, ribose and a base. There are five bases, respectively, adenine (A), guanine (G), cytosine (C), thymine (T) and uracil (U). Each contains only the five nucleotide base pairs in one. Even a single nucleotide into a chain, linked by two nucleotide a certain order, and then twisted into a "Serratula" kind, a deoxyribonucleic acid (DNA) of the molecular structure. In this structure, every three bases can form a genetic "password" and a DNA base pairs on as many as several million, so each DNA is a significant genetic code books, the inside of the genetic information In countless more, this DNA molecule found in the nucleus on the chromosome. They will pass with cell division genetic code. The genetic traits from the password to pass. Probably have 25,000 genes, and each gene is determined by the password. The same gene in both parts have different parts. Different parts of the difference between people decided that human diversity. A total of 3 billion DNA genetic code, are composed of about 25,000 genes. [Structure] [Edit this paragraph] DNA is composed of many deoxynucleotidyl residues with each other by a certain order of 3 ', 5'-phosphate ester bond linked to a long chain. Most of DNA containing two such long-chain, and some DNA for single-chain, such as E. coli phage φ X174, G4, M13, and so on. Some DNA for the ring, some for the linear DNA. Mainly with adenine, guanine, thymine and cytosine four kinds of bases. In some types of DNA, 5 - cytosine-to a certain extent can replace the CD, wheat germ DNA of 5 - methyl cytosine particularly rich, up 6 percent Moore. In some phage, 5 - hydroxymethyl cytosine replaced the CD. The late 1940s, Chargaff (E. Chargaff) found that different species of DNA base pairs of different, but the number of adenine equivalent to the number of its thymine (A = T), guanine cytosine equal to the number of (G = C), and thus the number of purine equivalent to the number of and pyrimidine. General painted with several levels of DNA structure. A structure of DNA in a structure that is its base sequence. Gene is a fragment of DNA, the genetic information stored in its genetic sequence of. 1975 U.S. Gilbert (W. Gilbert) and the United Kingdom Sanger (F. Sanger) respectively, created the structure of DNA a rapid determination of their total for the year 1980 Nobel Prize in Chemistry. Since then, determination and constantly improved, many of the DNA structure of an established. If people ring of mitochondrial DNA contains 16,569 base pairs, λ phage containing 48,502 DNA base pairs, rice chloroplast genome of 134,525 base pairs, tobacco chloroplast genome of 155,844 base pairs, and so on. Now the U.S. has plans to 10-15 years in all human DNA molecule of about 3 billion nucleotide pairs out of sequence. Secondary structure in 1953, Watson (Watson) and Crick (Crick) to the basic structure of DNA fibers is the double helix structure, but this model, the scientists acknowledged, and to explain reproduction, transcription and other important life process. After in-depth study and found that because of humidity and the base sequence of different conditions, DNA double helix can have many types, mainly divided into A, B and Z three categories. Is generally believed that, B configuration of the nearest cell in the DNA conformation, it is the double helix model is very similar. A-DNA and RNA molecules in the double helix, as well as the formation of transcription, DNA-RNA hybrid molecular conformation close. Z-DNA nucleotide dimer as a unit to the left to the winding, its main chain was serrated (Z) form, Gu Ming. This configuration of the chain for more than purine nucleotide pyrimidine alternate area. 1989, U.S. scientists used scanning tunneling electron microscope method to directly observe the DNA double helix DNA double helix: in 1952, Austria-American biochemists Chargaff (E.chargaff, 1905 -) of the DNA base pairs in the four kinds of Content found gland fat methotrexate and equal to the number of thymine, cytosine bird fat methotrexate and the number of the same. This makes Watson, Crick immediately think of four kinds of bases exists between the corresponding relations between February 2 and formed a gland fat methotrexate and thymine pairs, the birds fat methotrexate cytosine pairs with the conc

DNA Workshop Activity

An embryonic cell divides again and again. Where there was one cell there are two, then four, then eight,... Each holds all the genetic information needed to create a human being. How, exactly, do these cells make copies of themselves?
Hair grows from your head, nonstop, day in and day out. The cells of your hair follicles somehow generate all of the protein that make up this hair. How is this protein created?
The answers to these questions are DNA replication and protein synthesis.
Knowledge of the structure of DNA began with the discovery of nucleic acids in 1869. That genes control the synthesis of enzymes was understood in the 1940s. In 1953, an accurate model of the DNA molecule was presented, thanks to the work of Rosalind Franklin, James Watson, and Francis Crick.
The activity in this section places you within the cell, involving you with the processes of DNA replication and protein synthesis.

DNA test Ancestry

The Haplogroup A lineage has been subdivided into several subgroups A1 to A5. Most Native Americans that are Haplogroup A, fall into the sub group A2 which has the DNA motif 16111T, 16223T, 16290T, 16319A, 16362C. Sub group A3 carries the Beringian-specific 16192T. Haplogroup A4 is very widely spread in Asia, representing about 10% of Chinese. Haplogroup A5 appears to be isolated to the Japanese and Koreans.
The Ice Maiden belonged to Haplogroup A. She was a12-14 year old girl who was apparently sacrificed by Inca priests 500 years ago. She was a frozen and well preserved mummy, discovered in September 1995 on Mt. Ampato in the Peruvian Andes by anthropologist Johan Reinhard and Miguel Zarate. Her mtDNA was analyzed at The Institute for Genomic Research in Rockville, Maryland. Some mtDNA from a heart sample was analyzed and scientists concluded that the Ice Maiden belonged to the native American Indian Haplogroup A. Scientists concluded that she was slender in build, had not suffered any illness, had perfect teeth and strong bones, and had a well balanced diet. She appeared to have fasted one day before sacrifice and had a fissure to the skull.
3. His Common Male DNA Test results showed that his paternal lineage traced back to a man who belonged to Haplogroup O. His Common Male Certificate had the following DNA test results:

DNA test Ancestry

The Haplogroup A lineage has been subdivided into several subgroups A1 to A5. Most Native Americans that are Haplogroup A, fall into the sub group A2 which has the DNA motif 16111T, 16223T, 16290T, 16319A, 16362C. Sub group A3 carries the Beringian-specific 16192T. Haplogroup A4 is very widely spread in Asia, representing about 10% of Chinese. Haplogroup A5 appears to be isolated to the Japanese and Koreans.
The Ice Maiden belonged to Haplogroup A. She was a12-14 year old girl who was apparently sacrificed by Inca priests 500 years ago. She was a frozen and well preserved mummy, discovered in September 1995 on Mt. Ampato in the Peruvian Andes by anthropologist Johan Reinhard and Miguel Zarate. Her mtDNA was analyzed at The Institute for Genomic Research in Rockville, Maryland. Some mtDNA from a heart sample was analyzed and scientists concluded that the Ice Maiden belonged to the native American Indian Haplogroup A. Scientists concluded that she was slender in build, had not suffered any illness, had perfect teeth and strong bones, and had a well balanced diet. She appeared to have fasted one day before sacrifice and had a fissure to the skull.
3. His Common Male DNA Test results showed that his paternal lineage traced back to a man who belonged to Haplogroup O. His Common Male Certificate had the following DNA test results:

PCR EXPLAINED IN EASY TERMS

RFLP has been almost entirely replaced by PCR-based testing. The following description of RFLP is included here primarily for historic reasons (more current formats see below).
RFLP DNA testing has four basic steps:
1. The DNA from crime-scene evidence or from a reference sample is cut with something called a restriction enzyme. enzyme recognizes a particular short sequence such as AATT that occurs many times in a given cell's DNA. One enzyme commonly used is called Hae III (pronounced: Hay Three) but the choice of enzyme varies. For RFLP to work, the analyst needs thousands of cells. If thousands of a single individual, they will all be cut in same place along their DNA by the enzyme because each cells DNA is identical to every other cell of that person.
2. The cut DNA pieces are now sorted according to size by a device called a gel. The DNA is placed at one end of a slab of gelatin and it is drawn through the gel by an electric current. The gel acts like a sieve allowing small DNA fragments to move more rapidly than larger ones.
3. After the gel has separated the DNA pieces according to size, a blot or replica of the gel is made to trap the DNA in the positions that up in, with small DNA fragments near one end of the blot and large ones near the other end. The blot is now treated with a piece of DNA called a probe. The probe is simply a piece of DNA that binds to the DNA on the blot in the position were a similar sequence (the target sequence) is located.
4. The size or sizes of the target DNA fragments recognized by the probe are measured. Using the same probe and enzyme, the test lab will perform these same steps for many people. These sizes and how they distribute among large groups of a database. From the database a rough idea of how common a given DNA size measured by a given probe is found. The commonness of a given size of DNA fragment is called a population frequency.

The restriction enzyme cuts the DNA into thousands of fragments of nearly all possible sizes. The sample is then electrophoretically separated. The DNA at this point is invisible in the gel unless the DNA is stained with a dye. A replica of the gel's DNA something called a blot (also called a Southern blot) or membrane. The blot is then probed (mixed with) a special preparation of DNA that DNA sequence or locus. Often, the probe is a radioactively labeled DNA sequence (represented by * labeled object in the figure above). Excess probe is washed off the blot, then the blot is la onto X-ray film. Development reveals bands indicating the sizes of the alleles for the locus within each sample. The film is now called an "autorad." The band sizes are measured by comparing them with a "ladder" of known DNA sizes that is run next to the sample. A match may be declared if two samples have RFLP band sizes that are all within 5% of one another in size.

DNA test

To investigate the reliability and feasibility of human papillomavirus (HPV) DNA test in cervical scraping smears with polymerase chain reaction (PCR), 131 cases of cervical scraping specimens were collected, and the positive rates and accuracy of HPV infection were determined in normal subjects and cervical cancer patients. GP5+/GP6+ and E7 primer pairs designed for detecting HPV L1 and HPV type 16 E7 were tested in this study. Our results showed that positive rates of HPV DNA in normal population and cervical cancer patients were 32.99 ％ and 73.53 ％ respectively and there was significant difference between them (P＜0. 001). In normal subjects, detection rates of HPV DNA with GP5+/GP6+ and E7 primer pairs were 27.84 ％ and 16.49 ％ respectively, with statistically significant difference between them (P＞0.05). However the detection rates in cervical cancer patients were 38.24 ％ and 67.65 ％ for the two markers, with a significant difference found between them (P＜0.05). It is concluded that HPV DNA test with PCR for cervical scraping smears was feasible. GP5+/GP6+ primer pairs may be a useful probe to screen HPV infection in normal population, but they are not sensitive enough in cervical cancer patients. It is suggested that high risk type HPV DNA test was very useful in population with high risk of cervical cancer.
Michael Lohan is having a DNA test to determine if he is the father of a 13-year-old girl. Lindsay Lohan's dad is alleged to have had a year-long romance with Kristi Kaufmann, who claims he fathered her daughter Ashley while he was estranged from Lindsay's mom Dina. She said: "We were in love

Structure of DNA

in a nucleotide, the atoms of the organic base are numbered 1, 2, ... and the atoms of the sugar, wether it is a deoxyribose like in DNA or a ribose like in RNA, are numbered 1', 2', 5'. Atoms in the sugar component of a nucleotide provide the link between the base and the phosphate group. The 1' carbon is attached to the 9 nitrogen of a purine, or the 1 nitrogen of a pyrimidine. The OH (hydroxyl) group on the 5' carbon is replaced by a bond to the phosphate group (ester bond).
DNA consists of two associated polynucleotide strands that wind together in a helical fashion. It is often described as a double helix.
Each polynucleotide is a linear polymer in which the monomers (deoxynucleotides), are linked together by means of phosphodiester bridges , or bonds. These bonds link the 3' carbon in the ribose of one deoxynucleotide to the 5' carbon in the ribose of the adjacent deoxynucleotide. This is illustrated in Figure The structure of DNA is illustrated by a right handed double helix, with about 10 nucleotide pairs per helical turn. Each spiral strand, composed of a sugar phosphate backbone and attached bases, is connected to a complementary strand by hydrogen bonding (non- covalent) between paired bases, adenine (A) with thymine (T) and guanine (G) with cytosine (C). Adenine and thymine are connected by two hydrogen bonds (non

DNA replication

The hydrogen bonds between the strands of the double helix are weak enough that they can be easily separated by enzymes. Enzymes known as helicases unwind the strands to facilitate the advance of sequence-reading enzymes such as DNA polymerase. The unwinding requires that helicases chemically cleave the phosphate backbone of one of the strands so that it can swivel around the other. The stands can also be separated by gentle heating, as used in PCR, provided they have fewer than about 10,000 base pairs (10 kilobase pairs, or 10 kbp). The intertwining of the DNA strands makes long segments difficult to separate.
When the ends of a piece of double-helical DNA are joined so that it forms a circle, as in plasmid DNA, the strands are topologically knotted. This means they cannot be separated by gentle heating or by any process that does not involve breaking a strand. The task of unknotting topologically linked strands of DNA falls to enzymes known as topoisomerases. Some of these enzymes unknot circular DNA by cleaving two strands so that another double-stranded segment can pass through. Unknotting is required for the replication of circular DNA as well as for various types of recombination in linear DNA.
Space-filling model of a section of DNA molecule
The DNA helix can assume one of three slightly different geometries, of which the "B" form described by James D. Watson and Francis Crick is believed to predominate in cells. It is 2 nanometers wide and extends 3.4 nanometers per 10 bp of sequence. This is also the approximate length of sequence in which the helix makes one complete turn about its axis. This frequency of twist (known as the helical pitch) depends largely on stacking forces that each base exerts on its neighbors in the chain.
The narrow breadth of the double helix makes it impossible to detect by conventional electron microscopy, except by heavy staining. At the same time, the DNA found in many cells can be macroscopic in length -- approximately 5 centimeters long for strands in a human chromosome. Consequently, cells must compact or "package" DNA to carry it within them. This is one of the functions of the chromosomes, which contain spool-like proteins known as histones, around which DNA winds. The B form of the DNA helix twists 360° per 10.6 bp in the absence of strain. But many molecular biological processes can induce strain. A DNA segment with excess or insufficient helical twisting is referred to, respectively, as positively or negatively "supercoiled". DNA in vivo is typically negatively supercoiled, which facilitates the unwinding of the double-helix required for RNA transcription.
The two other known double-helical forms of DNA, called A and Z, differ modestly in their geometry and dimensions. The A form appears likely to occur only in dehydrated samples of DNA, such those used in crystallography experiments, and possibly in hybrid pairings of DNA and RNA strands. Segments of DNA that cells have methylated for regulatory purposes may adopt the Z geometry, in which the strands turn about the helical axis like a mirror image of the B form.
DNA sequence reading
The asymmetric shape and linkage of nucleotides means that a DNA strand always has a discernable orientation or directionality. Because of this directionality, close inspection of a double helix reveals that, although the nucleotides along one strand are heading one way (e.g. the "ascending strand") the others are heading the other (e.g. the "descending strand"). This arrangement of the strands is called antiparallel.
For reasons of chemical nomenclature, people who work with DNA refer to the asymmetric termini of each strand as the 5' and 3' ends (pronounced "five prime" and "three prime"). DNA workers and enzymes alike always read nucleotide sequences in the "5' to 3' direction". In a vertically oriented double helix, the 3' strand is said to be ascending while the 5' strand is said to be descending.
As a result of their antiparallel arrangement and the sequence-reading preferences of enzymes, even if both strands carried identical instead of complementary sequences, cells could properly translate only one of them. The other strand a cell can only read backwards. Molecular biologists call a sequence "sense" if it is translated or translatable, and they call its complement "antisense". It follows then, somewhat paradoxically, that the template for transcription is the antisense strand. The resulting transcript is an RNA replica of the sense strand and is itself sense.
Some viruses blur the distinction between sense and antisense, because certain sequences of their genomes do double duty, encoding one protein when read 5' to 3' along one strand, and a second protein when read in the opposite direction along the other strand. As a result, the genomes of these viruses are unusually compact for the number of genes they contain, which biologists view as an adaptation. Topologists like to note that the juxtaposition of the 3' end of one DNA strand beside the 5' end of the other at both termini of a double-helical segment makes the arrangement a "crab canon".
Single-stranded DNA (ssDNA) and repair of mutations
In some viruses DNA appears in a non-helical, single-stranded form. Because many of the DNA repair mechanisms of cells work only on paired bases, viruses that carry single-stranded DNA genomes mutate more frequently than they would otherwise. As a result, such species may adapt more rapidly to avoid extinction. The result would not be so favorable in more complicated and more slowly replicating organisms, however, which may explain why only viruses carry single-stranded DNA. These viruses presumably also benefit from the lower cost of replicating one strand versus two.
The discovery of DNA and the double helix
Working in the 19th century, biochemists initially isolated DNA and RNA (mixed together) from cell nuclei. They were relatively quick to appreciate the polymeric nature of their "nucleic acid" isolates, but realized only later that nucleotides were of two types--one containing ribose and the other deoxyribose. It was this subsequent discovery that led to the identification and naming of DNA as a substance distinct from RNA.
Friederich Miescher (1844-1895) discovered a substance he called "nuclein" in 1869. Somewhat later he isolated a pure sample of the material now known as DNA from the sperm of salmon, and in 1889 his pupil, Richard Altmann, named it "nucleic acid". This substance was found to exist only in the chromosomes. Max Delbrück, Nikolai V. Timofeeff-Ressovsky, and Karl G. Zimmer published results in 1935 suggesting that chromosomes are very large molecules the structure of which can be changed by treatment with X-rays, and that by so changing their structure it was possible to change the heritable characteristics governed by those chromosomes. (Delbrück and Salvador Luria were awarded the Nobel Prize in 1969 for their work on the genetic structure of viruses.) In 1943, Oswald Theodore Avery discovered that traits proper to the "smooth" form of the Pneumococcus could be transferred to the "rough" form of the same bacteria merely by making the killed "smooth" (S) form available to the live "rough" (R) form. Quite unexpectedly, the living R Pneumococcus bacteria were transformed into a new strain of the S form, and the transferred S characteristics turned out to be heritable.
In 1944, the renowned physicist, Erwin Schrödinger, published a brief book entitled What is Life?, in which he maintained that chromosomes contained what he called the "hereditary code-script" of life. He added: "But the term code-script is, of course, too narrow. The chromosome structures are at the same time instrumental in bringing about the development they foreshadow. They are law-code and executive power -- or, to use another simile, they are architect's plan and builder's craft -- in one." He conceived of these dual functional elements as being woven into the molecular structure of chromosomes. By understanding the exact molecular structure of the chromosomes one could hope to understand both the "architect's plan" and also how that plan was carried out through the "builder's craft." Francis Crick, James Watson, Maurice Wilkins, Seymour Benzer, et al., took up the physicist's challenge to work out the structure of the chromosomes and the question of how the segments of the chromosomes that were conceived to relate to specific traits could possibly do their jobs.
Just how the presence of specific features in the molecular structure of chromosomes could produce traits and behaviors in living organisms was unimaginable at the time. Because chemical dissection of DNA samples always yielded the same four nucleotides, the chemical composition of DNA appeared simple, perhaps even uniform. Organisms, on the other hand, are fantastically complex individually and widely diverse collectively. Geneticists did not speak of genes as conveyors of "information" in such words, but if they had, they would not have hesitated to quantify the amount of information that genes need to convey as vast. The idea that information might reside in a chemical in the same way that it exists in text--as a finite alphabet of letters arranged in a sequence of unlimited length--had not yet been conceived. It would emerge upon the discovery of DNA's structure, but few researchers imagined that DNA's structure had much to say about genetics.
In the 1950s, only a few groups made it their goal to determine the structure of DNA. These included an American group led by Linus Pauling, and two groups in Britain. At Cambridge University, Crick and Watson were building physical models using metal rods and balls, in which they incorporated the known chemical structures of the nucleotides, as well as the known position of the linkages joining one nucleotide to the next along the polymer. At King's College, London, Maurice Wilkins and Rosalind Franklin were examining x-ray diffraction patterns of DNA fibers.
A key inspiration in the work of all of these teams was the discovery in 1948 by Pauling that many proteins included helical (see alpha helix) shapes. Pauling had deduced this structure from x-ray patterns. Even in the initial crude diffraction data from DNA, it was evident that the structure involved helices. But this insight was only a beginning. There remained the questions of how many strands came together, whether this number was the same for every helix, whether the bases pointed toward the helical axis or away, and ultimately what were the explicit angles and coordinates of all the bonds and atoms. Such questions motivated the modeling efforts of Watson and Crick.
In their modeling, Watson and Crick restricted themselves to what they saw as chemically and biologically reasonable. Still, the breadth of possibilities was very wide. A breakthrough occurred in 1952, when Erwin Chargaff visited Cambridge and inspired Crick with a description of experiments Chargaff had published in 1947. Chargaff had observed that the proportions of the four nucleotides vary between one DNA sample and the next, but that for particular pairs of nucleotides -- adenine and thymine, guanine and cytosine -- the two nucleotides are always present in equal proportions.
Watson and Crick had begun to contemplate double helical arrangements, and they saw that by reversing the directionality of one strand with respect to the other, they could provide an explanation for Chargaff's puzzling finding. This explanation was the complementary pairing of the bases, which also had the effect of ensuring that the distance between the phosphate chains did not vary along a sequence. Watson and Crick were able to discern that this distance was constant and to measure its exact value of 2 nanometers from an X-ray pattern obtained by Franklin. The same pattern also gave them the 3.4 nanometer-per-10 bp "pitch" of the helix. The pair quickly converged upon a model, which they announced before Franklin herself published any of her work.
The great assistance Watson and Crick derived from Franklin's data has become a subject of controversy, and it has angered people who believe Franklin has not received the credit due to her. The most controversial aspect is that Franklin's critical X-ray pattern was shown to Watson and Crick without Franklin's knowledge or permission. Wilkins showed it to them at his lab while Franklin was away.
Watson and Crick's model attracted great interest immediately upon its presentation. Arriving at their conclusion on February 21, 1953, Watson and Crick made their first announcement on February 28. Their paper 'A Structure for Deoxyribose Nucleic Acid' was published on April 25. In an influential presentation in 1957, Crick laid out the "Central Dogma", which foretold the relationship between DNA, RNA, and proteins, and articulated the "sequence hypothesis." A critical confirmation of the replication mechanism that was implied by the double-helical structure followed in 1958 in the form of the Meselson-Stahl experiment. Work by Crick and coworkers deciphered the genetic code not long afterward. These findings represent the birth of molecular biology. Watson, Crick, and Wilkins were awarded a Nobel Prize in 1962, by which time Franklin had d
Deoxyribonucleic acid (DNA) is the primary chemical component of chromosomes and is the material of which genes are made. It is sometimes called the "molecule of heredity," because parents transmit copied portions of their own DNA to offspring during reproduction, and because they propagate their traits by doing so.
In bacteria and other simple or prokaryotic cell organisms, DNA is distributed more or less throughout the cell. In the complex or eukaryotic cells that make up plants, animals and in other multi-celled organisms, most of the DNA resides in the cell nucleus. The energy-generating organelles known as chloroplasts and mitochondria also carry DNA, as do many viruses.
Overview of molecular structure
Although sometimes called "the molecule of heredity," pieces of DNA as people typically think of them are not single molecules. Rather, they are pairs of molecules, which entwine like vines to form a double helix (top half of the illustration at the right).
Each vine-like molecule is a strand of DNA: a chemically linked chain of nucleotides, each of which consists of a sugar, a phosphate and one of four kinds of aromatic "bases". Because DNA strands are composed of these nucleotide subunits, they are polymers
Because pairing causes the nucleotide bases to face the helical axis, the sugar and phosphate groups of the nucleotides run along the outside, and the two chains they form are sometimes called the "backbones" of the helix. In fact, it is chemical bonds between the phosphates and the sugars that link one nucleotide to the next in the DNA strand