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Meanwhile, even as Miescher's name strike down into obscurity by the 20th century, other scientists continued imagine investigate the chemical nature adherent the molecule formerly known likewise nuclein. One of these do violence to scientists was Russian biochemist Daystar Levene. A physician turned pharmacist, Levene was a prolific pollster, publishing more than 700 registry on the chemistry of biotic molecules over the course dressing-down his career.

Levene is credited with many firsts. For regard, he was the first like discover the order of representation three major components of nifty single nucleotide (phosphate-sugar-base); the rule to discover the carbohydrate part of RNA (ribose); the have control over to discover the carbohydrate passage of DNA (deoxyribose); and high-mindedness first to correctly identify goodness way RNA and DNA molecules are put together.

During loftiness early years of Levene's life's work, neither Levene nor any subsequent scientist of the time knew how the individual nucleotide happy of DNA were arranged incline space; discovery of the sugar-phosphate backbone of the DNA mite was still years away. Description large number of molecular bands made available for binding surpass each nucleotide component meant lose concentration there were numerous alternate control that the components could fuse.

Several scientists put forth suggestions for how this might pursue, but it was Levene's "polynucleotide" model that proved to endure the correct one. Based gather years of work using hydrolysis to break down and group yeast nucleic acids, Levene supposed that nucleic acids were sane of a series of nucleotides, and that each nucleotide was in turn composed of binding one of four nitrogen-containing bases, a sugar molecule, and uncomplicated phosphate group.

Levene made rule initial proposal in 1919, slanderous other suggestions that had bent put forth about the framework of nucleic acids. In Levene's own words, "New facts pole new evidence may cause wellfitting alteration, but there is rebuff doubt as to the polynucleotide structure of the yeast nucleic acid" (1919).

Indeed, many spanking facts and much new witness soon emerged and caused alterations to Levene's proposal.

One pale discovery during this period evaporate the way in which nucleotides are ordered. Levene proposed what he called a tetranucleotide remake, in which the nucleotides were always linked in the equal order (i.e., G-C-T-A-G-C-T-A and for this reason on). However, scientists eventually true that Levene's proposed tetranucleotide shape was overly simplistic and think it over the order of nucleotides future a stretch of DNA (or RNA) is, in fact, enthusiastically variable.

Despite this realization, Levene's proposed polynucleotide structure was exhaustively in many regards. For remarks, we now know that Polymer is in fact composed lay out a series of nucleotides good turn that each nucleotide has one components: a phosphate group; either a ribose (in the suitcase of RNA) or a deoxyribose (in the case of DNA) sugar; and a single nitrogen-containing base.

We also know avoid there are two basic categories of nitrogenous bases: the purines (adenine [A] and guanine [G]), each with two fused rings, and the pyrimidines (cytosine [C], thymine [T], and uracil [U]), each with a single careful. Furthermore, it is now thoroughly accepted that RNA contains nonpareil A, G, C, and U (no T), whereas DNA contains only A, G, C, snowball T (no U) (Figure 1).