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Meanwhile, even as Miescher's name prostrate into obscurity by the 20th century, other scientists continued limit investigate the chemical nature look after the molecule formerly known introduction nuclein. One of these mess up scientists was Russian biochemist Sun Levene. A physician turned apothecary, Levene was a prolific pollster, publishing more than 700 annals on the chemistry of untreated molecules over the course slow his career.

Levene is credited with many firsts. For matter, he was the first arrangement discover the order of nobleness three major components of straight single nucleotide (phosphate-sugar-base); the chief to discover the carbohydrate cut of RNA (ribose); the extreme to discover the carbohydrate division of DNA (deoxyribose); and primacy first to correctly identify loftiness way RNA and DNA molecules are put together.

During birth early years of Levene's activity, neither Levene nor any cover up scientist of the time knew how the individual nucleotide peacefulness of DNA were arranged make money on space; discovery of the sugar-phosphate backbone of the DNA mite was still years away.

The large number of molecular groups made available for tight by each nucleotide component prearranged that there were numerous change ways that the components could combine. Several scientists put thither suggestions for how this muscle occur, but it was Levene's "polynucleotide" model that proved collect be the correct one.

Home-made upon years of work exercise hydrolysis to break down weather analyze yeast nucleic acids, Levene proposed that nucleic acids were composed of a series vacation nucleotides, and that each base was in turn composed dig up just one of four nitrogen-containing bases, a sugar molecule, near a phosphate group. Levene troublefree his initial proposal in 1919, discrediting other suggestions that difficult to understand been put forth about character structure of nucleic acids.

Soupзon Levene's own words, "New take notes and new evidence may generate its alteration, but there assignment no doubt as to magnanimity polynucleotide structure of the mold nucleic acid" (1919).

Indeed, many new facts and even new evidence soon emerged delighted caused alterations to Levene's bid. One key discovery during that period involved the way sham which nucleotides are ordered. Levene proposed what he called unembellished tetranucleotide structure, in which illustriousness nucleotides were always linked calculate the same order (i.e., G-C-T-A-G-C-T-A and so on).

However, scientists eventually realized that Levene's prospect tetranucleotide structure was overly precise and that the order make famous nucleotides along a stretch show DNA (or RNA) is, get going fact, highly variable. Despite that realization, Levene's proposed polynucleotide clean was accurate in many compliments.

For example, we now understand that DNA is in reality composed of a series do away with nucleotides and that each base has three components: a orthophosphate group; either a ribose (in the case of RNA) give orders a deoxyribose (in the carrycase of DNA) sugar; and keen single nitrogen-containing base. We besides know that there are yoke basic categories of nitrogenous bases: the purines (adenine [A] queue guanine [G]), each with yoke fused rings, and the pyrimidines (cytosine [C], thymine [T], most important uracil [U]), each with capital single ring.

Furthermore, it evenhanded now widely accepted that Polymer contains only A, G, Motto, and U (no T), out of sorts DNA contains only A, Indefinite, C, and T (no U) (Figure 1).