Watson and crick model of DNA
Watson and Crick Model of DNA
Many people think that in the 1950s, English physicist Francis Crick and American biologist James Watson discovered DNA. This is not the situation in actuality. Rather, Swiss chemist Friedrich Miescher discovered DNA for the first time in the late 1860s. Then, in the decades that followed Miescher's discovery, a number of studies conducted by other scientists—most notably, Phoebus Levene and Erwin Chargaff—uncovered more information about the DNA molecule, including its main chemical constituents and the ways in which they interacted with one another. Watson and Crick may never have come to their ground-breaking conclusion in 1953—that the DNA molecule exists as a three-dimensional double helix—without the scientific groundwork laid by these pioneers.
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The year 1869, albeit little known to most, was a turning point in the history of genetics study since it was the year when Swiss physiological chemist Friedrich Miescher discovered what he later named "nuclein" within the nuclei of human white blood cells. (This term "nuclein" was soon replaced with "nucleic acid" and then with "deoxyribonucleic acid," or "DNA.") Miescher's strategy was to separate and analyze the protein constituents of leukocytes, or white blood cells, rather than the nuclein, which no one at the time knew existed.
Meanwhile, other scientists carried on studying the chemical properties of the molecule formerly known as nuclein, even as Miescher's name faded into obscurity by the twentieth century. Phoebus Levene, a Russian biochemist, was one of these other scientists. Levene, a doctor who later became a chemist, was a prolific researcher who over his career published over 700 publications on the chemistry of biological substances. Levene has numerous firsts to his name. He was the first to correctly identify the order in which phosphate, sugar, and base are the three major components of a single nucleotide, for example. He was also the first to identify the carbohydrate component of RNA, which is called ribose, and the carbohydrate component of DNA, which is called deoxyribose.
A small group of scientists, including Erwin Chargaff, built on Levene's work by discovering further information about the DNA molecule's structure, so opening the door for Watson and Crick. The renowned 1944 study by Oswald Avery and his colleagues at Rockefeller University, which proved that genetic units, or genes, are made of DNA, was read by Austrian biologist Chargaff.
Firstly, he pointed out that different species' DNAs had different nucleotide compositions. Put otherwise, Levene's proposal is not true—that is, the same nucleotides do not repeat in the same order. Second, Chargaff came to the conclusion that nearly all DNA, regardless of the organism or tissue type it originates from, retains a set of characteristics despite compositional variations. Specifically, the quantity of adenine (A) typically resembles that of thymine (T), while the quantity of guanine (G) typically like that of cytosine (C). Stated otherwise, the total quantity of pyrimidines (C + T) and purines (A + G) is typically almost equal. (This second important finding is currently referred to as "Chargaff's rule.")
The two key pieces of information that Chargaff used to help Watson and Crick derive their three-dimensional, double-helical model of DNA's structure were some very significant X-ray crystallography work by English researchers Rosalind Franklin and Maurice Wilkins, and the realization that A = T and C = G. Recent developments in model building, or the assembly of hypothetical three-dimensional structures based upon known chemical distances and bond angles, a technique developed by American biologist Linus Pauling, also contributed to Watson and Crick's finding. Just months before they did, Pauling had offered an alternate hypothesis for the three-dimensional structure of DNA, and Watson and Crick were actually concerned that they would be "scooped" by this rival. Ultimately, though, Pauling's forecast proved to be inaccurate.
Watson and Crick moved molecules about on their workstations, like they were assembling a jigsaw, using cardboard cutouts that represented the distinct chemical components of the four bases and other nucleotide subunits. For a while, they were duped by a false perception of the configurations of the various components in thymine and guanine, namely the rings of carbon, nitrogen, hydrogen, and oxygen. Watson decided to create new cardboard cutouts of the two bases only at the suggestion of American physicist Jerry Donohue, in an attempt to determine whether a different arrangement of the atoms may have an effect. Yes, it did. Now that the complementary bases (A with T and C with G) were precisely matched and bound together by hydrogen bonds, the structure also.
Watson and Crick moved molecules about on their workstations, like they were assembling a jigsaw, using cardboard cutouts that represented the distinct chemical components of the four bases and other nucleotide subunits.
For a while, they were duped by a false perception of the configurations of the various components in thymine and guanine, namely the rings of carbon, nitrogen, hydrogen, and oxygen. Watson decided to create new cardboard cutouts of the two bases only at the suggestion of American physicist Jerry Donohue, in an attempt to determine whether a different arrangement of the atoms may have an effect. Yes, it did. Now that the complementary bases (A with T and C with G) were precisely matched and bound together by hydrogen bonds, the structure also The DNA double helix is anti-parallel, which means that the 5' end of one strand is paired with the 3' end of its complementary strand (and vice versa). As shown in Figure 4, nucleotides are linked to each other by their phosphate groups, which bind the 3' end of one sugar to the 5' end of the next sugar.
Not only are the DNA base pairs connected via hydrogen bonding, but the outer edges of the nitrogen-containing bases are exposed and available for potential hydrogen bonding as well. These hydrogen bonds provide easy access to the DNA for other molecules, including the proteins that play vital roles in the replication and expression of DNAThe discovery that the DNA double helix exists in three distinct conformations is one way that researchers have expanded upon Watson and Crick's idea. Stated differently, the double helix's exact dimensions and geometries can change. B-DNA is the most prevalent shape in the majority of live cells, the one Watson and Crick postulated, and the one seen in most double helix diagrams. Two other conformations exist: Z-DNA, a left-handed conformation, and A-DNA, a shorter and wider form that has only sometimes been observed in normal physiological conditions and has been discovered in dehydrated DNA samples. Z-DNA is a temporary variant of DNA that only sporadically appears in reaction to specific biological activities.
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