Deoxyribonucleic acid: DNA, History about DNA
Deoxyribonucleic acid
Location of DNA within a cell.
Deoxyribonucleic acid, often abbreviated as DNA is a type of nucleic acid, a macromolecule that is part of all cells. Contains information genetics used in the development and functioning of living organisms known and some virus, responsible for transmitting hereditary.
From the standpoint of chemical, DNA is a polymer of nucleotides, ie a polynucleotide. A polymer is a compound consisting of many interconnected simple units, like a long train of wagons formed. In DNA, each coach is a nucleotide and each nucleotide, in turn, consists of a sugar (deoxyribose), a nitrogenous base (either adenine → A, thymine → T, cytosine → C or guanine → G ) and a group phosphate which acts as a hook of each carriage to the next. What distinguishes a wagon (nucleotide) of another, then, is the nitrogenous base, and therefore the DNA sequence is specified by naming only the sequence of bases. The sequential arrangement of these four bases along the chain (the ordering of the four types of cars along the entire train) is the one that encodes genetic information, eg a DNA sequence can be ATGCTAGATCGC .. . In living organisms, DNA is like a double chain of nucleotides, in which two strands are bound together by a connection called hydrogen bonds.
For the information contained in DNA can be used by the cellular machinery, must be copied first in a train of nucleotides, shorter and with a few different units, called RNA. The molecules of RNA, DNA is copied exactly by a process called transcription. Once processed in the cell nucleus, RNA molecules may leave the cytoplasm for subsequent use. The information contained in the RNA is interpreted using the genetic code, which specifies the sequence of amino acids in proteins, according to a correspondence one triplet of nucleotides (codon) for each amino acid. That is, the genetic information (essentially: what proteins are produced in every moment of the life cycle of a cell) has been encoded in the nucleotide sequences of DNA must be translated to be used. Such translation is performed using the genetic code as a dictionary. The dictionary "nucleotide sequence of the amino acid sequence allows the assembly of long chains of amino acids (proteins) in the cytoplasm of the cell. For example, in the case of the DNA sequence shown above (ATGCTAGATCGC. ..), RNA polymerase used as template the complementary strand of the DNA sequence (which would TAC-GAT-CTA-GCG-...) to transcribed mRNA molecule is read-GAU-CUA AUG-CGC-..., the resulting mRNA, using the genetic code, translates as the amino acid methionine - leucine - aspartic acid - arginine -...
The DNA sequences that constitute the fundamental unity of the physical and functional inheritance are called genes. Each gene contains a part that is transcribed into RNA and another that is responsible for defining when and where they express. The information contained in genes (genetic) is used to generate RNA and proteins, which are the building blocks of cells, the building blocks used for the construction of cellular organelles, among other functions.
Within cells, DNA is organized into structures called chromosomes that during the cell cycle is duplicated before the cell divides. The eukaryotic organisms (eg animals, plants, and fungi) store the vast majority of its DNA into the cell nucleus and a small part in the cellular components called mitochondria, and in the plastids, should have them; the prokaryotes ( bacteria and archaea) is stored in the cytoplasm of the cell, and finally, the DNA viruses do so within the capsid protein in nature. There are many proteins such as histones and transcription factors that bind to DNA by giving it a three-dimensional structure determined and regulating its expression. The transcription factors recognize DNA regulatory sequences and specify the pattern of gene transcription. The complete genetic material of a chromosome is called the genome and, with minor variations, is characteristic of each species.
History
Friedrich Miescher, Swiss physician who died in 1895.
DNA was first isolated during the winter of 1869 by the physician Swiss Friedrich Miescher while working at the University of Tubingen. Miescher conducted experiments on the chemical composition of pus from bandages surgical discarded when he noticed a precipitate of an unknown substance that chemically characterized later. He called it "nuclein" because it had extracted from the nuclei phones. It took almost 70 years of research to identify the components and structure of nucleic acids.
In 1919 Phoebus Levene identified as a nucleotide consists of a base, a sugar and a phosphate. Levene suggested that DNA formed a structure shaped solenoid (spring) nucleotide units linked by phosphate groups. In 1930 Levene and his master Albrecht Kossel nuclein proved that Miescher is a deoxyribonucleic acid (DNA) formed by four nitrogen bases (cytosine (C), thymine (T), adenine (A) and guanine (G)), sugar deoxyribose and a phosphate group, and that in its structure base, the nucleotide comprises a sugar attached to the base and phosphate. However, Levene thought the chain was short and the bases repeated in a fixed order. In 1937 William Astbury produced the first pattern of X-ray diffraction which showed that DNA had a regular structure.
Maclyn McCarty with Francis Crick and James D Watson.
The biological function of DNA began to be elucidated in 1928 with a basic set of modern genetics experiments conducted by Frederick Griffith, who was working with strains of "smooth" (S) or "rough" (R) of the bacterium Pneumococcus (which causes of pneumonia), according to the presence (S) or not (R) of a sugar capsule that is conferred virulence (see also Griffith's experiment). The injection of living S pneumococci in mice leads to death of them, and Griffith observed that mice injected with live R pneumococci or with heat-killed S pneumococci, the mice did not die. However, if injected with R pneumococci both living and dead S pneumococci, the mice died, and her blood could isolate living S pneumococci. As dead bacteria could not have multiplied inside the mouse, Griffith argued that it should have some form of change or transformation of a bacterial type to another by means of a transfer of an active substance, which he called "transforming principle". This substance provides the ability to produce R pneumococci sugar capsule and thus becoming virulent. Over the next 15 years, these initial experiments were duplicated by mixing different types of bacteria killed by heat with other live, both in mice (in vivo) and in test tubes (in vitro). The search of factor Transforming "that was capable of virulent strains that were not initially continued until 1944, in which Oswald Avery, Colin MacLeod and Maclyn McCarty performed a now classic experiment.
These researchers extracted the active moiety (the transforming factor) and by chemical analysis, enzymatic and serological, found that it contained protein and lipid unbound or active polysaccharides, but consisted mainly of "a thick form of deoxyribonucleic acid highly cured ", ie DNA. The DNA extracted from bacterial strains by heat killed S mixed it in vitro with living R strains: the result was that formed bacterial colonies S and therefore unequivocally concluded that the factor or transforming principle was DNA. Although the identification of DNA as transforming principle still took several years to be universally accepted, this discovery was crucial in understanding the molecular basis of heredity, and is the birth of molecular genetics. Finally, the exclusive role of DNA in the heritability was confirmed in 1952 through the experiments of Alfred Hershey and Martha Chase, where they found that the phage T2 transmitting genetic information in their DNA, but not its protein.
As for the chemical characterization of the molecule in 1940 Chargaff conducted some experiments that served to establish the proportions of the nitrogenous bases in DNA. He found that the proportions of purines were identical to those of pyrimidines, the "equimolar" bases ([A] = [T] [G] = [C]) and the number of G + C in a given molecule DNA is not always equal to the amount of A + T and can vary from 36% to 70% of the total. With this information and data along with X-ray diffraction provided by Rosalind Franklin, James Watson and Francis Crick proposed in 1953 the double helix model of DNA to represent the structure of three-dimensional polymer.In a series of five articles in the same issue of Nature was published experimental evidence supporting the model of Watson and Crick. Of these, the article by Franklin and Raymond Gosling was the first publication using data from X-ray diffraction supported the Watson-Crick model, and in this issue of Nature also featured an article on DNA structure of Maurice Wilkins and his collaborators.
In 1962, after Franklin's death, scientists Watson, Crick and Wilkins were jointly awarded the Nobel Prize in Physiology or Medicine. However, the debate continues over who should receive credit for the discovery.
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