Pyrimidine bases names

The names of these compounds as aza analogs were coined in the same way as those of the 6-aza analogs employing the frequently used numbering of uracil (1). This nomenclature is most often used for the principal aza analogs of pyrimidine bases (e.g., 5-azauracil) it is rarely used for further systematic derivatives. 

Attempts have been made to correlate these characteristics with the rate of photodimerization of a series of pyrimidine bases.467 1 Among these characteristics, two appeared to be particularly important for the photodimerization problem (for review see ref. 466), namely the density of the uncoupled electrons (or spin density) pf at C-5 and C-6 and the change of the C(5)-C(6) bond order P56 upon excitation. The proposal that the high concentration of spin density on the C(5)-C(6) bond as well as its low bond order in the excited states were factors responsible for the case of photodimerization was stated about ten years ago.464,471 The first calculations, within the framework of the 77-HMO approximation, showed the following findings (i) The concentration of uncoupled... 

Two types of heterocyclic N bases are found the pyrimidine bases (31), (32) and (33), and the purine bases (34) and (35). The pKt values are given in Table 10 as are the names of the compounds derived from the bases. One other difference between DNA and RNA is that the former is found to contain thymine, while the latter contains uracil. The average cell contains 2-5% of its dry weight as nucleic acids and nucleotides neither the heterocyclic bases nor the nucleosides occur as such in cells. 

The above-mentioned purine-pyrimidine base-pairing scheme consists, as it is well known, of hydrogen bonding between specific, complementary base pairs, namely, adenine-thymine [or uracil in ribonucleic acid (RNA)] and guanine-cytosine (Fig. 1) (shorthand notations A-T or A-U and G-C). The specificity of the bonding concerns both this exclusiveness and the steric arrangement which is... 

These complementarity rules owe their discovery to the chemical analysis of DNA by Chargaff and associates (3). The DNA from many different organisms shows the same patterns of base composition, namely A and T are always present in equal quantities, as are G and C. The immediate corollary of this observation, that a purine base (R) exists for every pyrimidine base (Y) and vice versa, led Watson and Crick to propose that two helical strands in DNA are held together by specific, intermolecular purine-pyrimidine (R Y) interactions (4). In turn, this unique chemical complementarity of the double-helical structure, proved to be a major breakthrough to understand the self-recognition and self-reproduction of DNA and forms the cornerstone of structmal biology as we know it today, more than half a century later. 

The nomenclature of nucleotides and their constituent units was presented earlier (Section 5.1.2). Recall that a nucleoside consists of a purine or pyrimidine base linked to a sugar and that a nucleotide is a phosphate ester of a nucleoside. The names of the major bases of RNA and DNA, and of their nucleoside and nucleotide derivatives, are... 

In the early attempts to identify the nitrogenous bases of desoxy-ribosenucleic acid, some confusion arose for two reasons. At first, the products obtained by hydrolysis of nucleoprotein were studied, and there was no assurance that any particular base came from the nucleic acid rather than from the protein. Then, when the nucleic acid itself became available, the hydrolytic agents at first employed were sufficiently drastic to cause some deamination of the amino-purines (with the production of some xanthine and hypoxanthine) and some demethylation of thymine to uracil. In 1874, Piccard isolated guanine (and h3T>oxanthine) from sperm nuclein. Kossel and Neumann discovered in the hydrolysate of thymus nucleic acid two new pyrimidine bases which they named thy-mine and cytosine but they assigned incorrect empirical formulas to them. In 1894, they correctly described thymine as CsHgOjNs, but cytosine was not purified and characterized till much later. " " Levene now analyzed a series of nucleic acids from a variety of sources and found " that they all contained guanine and adenine. By mild hydrolysis of thymus nucleic acid, Steudel obtained guanine and adenine as the sole purine bases and demonstrated that they occur in equi-molecular proportions. Levene and Mandel confirmed this result and showed that the two purine bases and the two pyrimidine bases (thymine and cytosine) all occur in thymus nucleic acid in equimolecular proportions. 

Nucleosides of 2-deoxyribose are named in the same way. Carbons in the carbohydrate portion of the molecule are identified as 1, 2, 3, 4, and 5 to distinguish them from atoms in the purine or pyrimidine base. Thus, the adenine nucleoside of 2-deoxyri-bose is called 2 -deoxyadenosine or 9-(3-2 -deoxyribofuranosyladenine. 

The rate constants for the single steps of the chain reaction, namely the coupling of radical with nucleophile, the electron transfer to the aromatic compound and the dissociation of the radical anion have been determined by electroanalytical techniques, and its scope by way of cathodic induction has been demonstrated [159]. The reaction has been extended to substrates other than aromatics. For example, perfluoroalkylation of purine and pyrimidine bases can be achieved by cathodic initiation [160[. 

The chemical composition of DNA, a long chained biopolymer, consists of a 2 -deoxyribose phosphate backbone with the four bases, namely adenine and guanine, the two purines, and thymine and cytosine, the two pyrimidines, attached through the C(l) position of the 2 -deoxyribose group by a P-glycosidic bond. The primary structure of one of the strands of DNA is shown in Figure 1. In its biological form DNA is double stranded and the two strands... 

Nomenclature Base name + idine (pyrimidine) or + osine (purine)... 

Nucelotides are the repeating building blocks of nucleic adds (which are polynucleotides or polymers of nucleotides). A nucleotide is made up of a het-erocycHc base (a purine or pyrimidine), a cychc sugar unit (ribose or deoxyri-bose), and a phosphate group. A nucleotide is either a ribonucleotide, the repeating unit in ribonucleic acid (RNA), or a deoxyribonudeotide, the repeating unit in deoxyribonucleic acid (DNA). Table 1 below fists the names of purine and pyrimidine bases, the nucleosides (base + ribose), the corresponding 5 -nucleotides (base + ribose + phosphate), and the abbreviations. 

As described above, the bases of DNA are composed of four structures, namely adenine and guanine (purine bases) and cytosine and thymine (pyrimidine bases). On the other hand, in the case of RNA, one of the four bases, uracil, is utilized instead of thymine of DNA within the four kinds of bases. Uracil possesses a structure in which the fifth methyl group of thymine is replaced with a hydrogen atom. 

Formaldehyde administered by larval feeding therefore induces a wide variety of major genetic effects, which contrasts with the simple base pair changes largely found to be induced by nucleic acid base-analogues in prokaryotes. Several mutagenic purine and pyrimidine base-analogues of this latter type have been tested on Drosophila larvae, but found not to induce mutation [10] namely, 2-aminopurine 2,6-diaminopurine 5-bromodeoxyuridine and 5-bromodeoxycytidine. 

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