Purine bases names

Purines (purine bases). Name for a group of important compounds that are widely distributed in nature and participate in human, animal, plant, and microbial metabolic processes. They are derived from the parent compound purine (C5H4N4, Mr 120.11, mp. 217 °C) by substitution with OH, NH2, SH groups in the in 2-, 6-,... 

The names of 2-aza analogs are derived by formal substitution of the methine group in the 2-position of the purine skeleton by a nitrogen atom (140). Since this position is substituted in some purine bases, only the aza analogs of adenine or hypoxanthine are amenable to such formal derivation. 

Deoxyribonucleic acids readily undergo hydrolysis whereby purine bases are removed to give a derived polynucleotide originally named thymic acid, but now often called apurinic acid. Hydrolysis may be carried out with dilute mineral acid, but recently apurinic acids have been prepared by fission at room temperature with an acidic, ion-exchange resin.236 Under carefully controlled conditions, removal of the purines can be performed quantitatively without destroying the polynucleotide nature of the material and without altering the inter-pyrimidine ratios of the original material.23 ... 

Alkaline hydrolysis splits the nucleotide into its phosphate and sugar-base residues. The sugar-base is known as a nucleoside. The nucleosides are named according to the type of base present. If a purine base is present it will end -osine, e.g. adenosine, while if a pyrimidine is present the name will end -idine, e.g. uridine. 

Names of Pyrimidine and Purine Bases, Nucleosides, and 5 -Nucleotidesa... 

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. 

Fig. 5 Structure of pyrimidine and purine and names of the related bases.

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. 

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. 

Purine salvage pathway The synthesis of purine nucleotides by the condensation of the purine bases with phosphoribosyl pyrophosphate. As the name suggests, it is a way in which purine bases can be recycled back to nucleotides. The purine salvage pathway consists of two enzymes, HGPRT and adenine phosphoribosyltransferase (APRT). 

Figure 1.74 Depiction of Z-form DNA. (pdb 331d) using Rings Display (side view) in which the anti-parallel phosphodiester backbones are shown as arrowed ribbons (green) ribose rings (green), purine bases (red) and pyrimidine (blue). This side view demonstrates how the phosphodiester backbone now takes on a "zig-zag" appearance, hence the name of this DNA conformation. This double helix is now left-handed.

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... 

Nucleotides are derived from three different types of molecules—phosphoric acid, pentose sugar, and heterocyclic nitrogen base (Fig. 21-1). Two different pentoses are used, o-ribose for RNA and 2-deoxy-D-ribose for DNA. Henceforth, the sugars will be referred to simply as ribose and deoxyri-bose. A total of five different heterocyclic bases are used, three pyrimidine and two purine bases. Each base is symbolized by the first letter of its name, C, T, U, A, and G for cytosine, thymine, uracil, adenine, and guanine, respectively. A, G, and C are used in synthesizing both DNA and RNA nucleotides. T is used only for DNA while U is used only for RNA. 

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

A nucleoside in which a hydroxyl group of one of the sugar moieties is esterified with a phosphoric acid is called a nucleotide. For example, placing a phosphate at the 5 -position of adenosine and guanosine, each possessing purine base, generates nucleotides, and these are named 5 -adenylic acid (AMP) and 5 -guanylic acid (GMP), respectively, and are utilized biochemically in the formation of ribonucleic acid (RNA). 

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. 

Controlled hydrolysis of nucleic acids yields three types of simpler building blocks heterocyclic aromatic amine bases, the monosaccharide D-ribose or 2-deoxy-D-ribose (Section 17.3), and phosphate ions. Figure 20.1 shows the five heterocyclic aromatic amine bases most common to nucleic acids. Uracil, cytosine, and thymine are referred to as pyrimidine bases after the name of the parent base adenine and guanine are referred to as purine bases. 

The comparison of the curves on Figure 3 with the analogous ones for 5 nucleotides [6] shows that for the protons of the bases the calculated A8 s as a function of f are qualitatively the same for both types of nucleotide. The differences are only numerical, the variations being smaller for 3 -nucleotides than for the 5 ones but in both cases the gg conformation (T - 60 ) corresponds to the minimum of the curves for H6 in pyrimidines and H8 in purines. Thus for any type of nucleotides a decrease in the population of the gg conformation about the C4 -C5 bond should produce an upfield shift of either H6 or H8, according to the type of the base. The chemical shift of the other protons of the bases namely H5, N3H or H2 are not influenced by the value of V as it was the case for 5 -nucleotides. We report on Figure 3 only the data for the C3 -endo ribose since the results are the same for the C2 -endo puckering with the sole difference that the calculated variations have absolute values about half of those for the C3 -endo puckering. 

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