Nucleotides Purine Pyrimidines

Purine Pyrimidine Nucleotide Biosynthesis Are Coordinately Regulated... 

The chemistry of nucleic acid analogs has received much attention in recent years, and a series of nucleic acid models has been designed and widely prepared, in order to estimate and utilize their functionalities in relation to the specific basepairing properties ( J., i, ). These monomers and polymers, particularly those containing purines, pyrimidines, nucleosides, and nucleotides, are not only of interest to the field of heterocyclic organic chemistry, but also to that of biomimetic macro-molecular chemistry as synthetic analogs of the nucleic acids. 

There are two types of nitrogen-containing bases commonly foimd in nucleotides purines and pyrimidines (F ure 1-1-4) ... 

Nucleic-acid-related molecules (nucleotides, nucleosides, purines, pyrimidines) may also be used as dmgs themselves (and not only as dmg receptors). Once again, as discussed in chapters 7 and 9, this is most relevant in the areas of cancer and infectious disease, with purine/pyrimidine analogs being exploited as antimetabolites. 5-Fluorouracil is a well-described antineoplastic agent. Analogously, 5-fluorocytosine is used as an antifungal... 

Nucleotide synthesis amino acids------> purines, pyrimidines... 

None of the extracts from unchlorinated model compounds were significantly different from the negative controls. Extracts of chlorinated purines-pyrimidines and chlorinated nucleosides-nucleotides were also found to be not significantly mutagenic. However, the extracts of all three chlorinated humic acids and the chlorinated amino acids were... 

Table 5.22. 13C Chemical Shifts (<5C in ppm) of Purines, Pyrimidines, Nucleosides and Nucleotides. 

The DNA molecule is composed of two parts. One is a repeating sequence of a 5-carbon sugar (deoxyribose) and phosphate that makes up the backbone of the molecule. The second part is one of four bases associated with each repeat unit in the backbone two purines, adenine (A) and guanine (G), and two pyrimidines, cytosine (C) and thymine (T). DNA consists of two vertical backbones bonded horizontally by a purine-pyrimidine pair at each sugar-phosphate unit. A purine or pyrimidine with its associated sugar and phosphate is called a nucleotide. ... 

Although the tegument contains specific systems for molecular and ion transport - especially amino acids, hexose sugars, vitamins, purines, pyrimidines, nucleotides, and lipids - it probably also serves a number of other vital functions (647) (a) it is a major site of catalytic activity and... 

In the study of 1352 hydrogen bonds of type NH -0=C [561, only 6 were regarded as four-centered, but this analysis used an arbitrary van der Waals cut-off criterion which may have biased the conclusions. In the carbohydrates, purines, pyrimidines, nucleosides, and nucleotides, the proportion was about or less than 1%. 

Table 7.19. Two-center )NH- -N bond lengths (A) in purines, pyrimidines (column A) and nucleosides and nucleotides (column B) (Mean effective equilibrium bond length in A [61])...

Table 8.8. Three-center chelated hydrogen-bond configurations observed in the crystal structure of the purines, pyrimidines, nucleosides and nucleotides (normalized from X-ray data)...

Configurations involving simultaneously three-center and bifurcated hydrogen bonds are observed in the crystal structures of nucleic acid constituents purines, pyrimidines, nucleosides, nucleotides. 

Table 8.11. Geometry of four-center bonds in the crystal structures of the purines, pyrimidines (P P), nucleosides and nucleotides (N N)...

Table 11.2. Summary of the two-center and three-center hydrogen-bond lengths to Cl ions in the purine, pyrimidine, nucleoside and nucleotide crystal structures, normalized from X-ray data...

The bases are in syn or anti orientation. The orientation of the base relative to the sugar moiety is defined by torsion angle x which is constrained by steric interactions, and by the anomeric effect. The main conformations are referred to as syn and anti (see Fig. 17.5). In syn, j X is close to 0° (sp for torsion angle definition, see Box 13.3 Fig. 13.12), and the base is I oriented "above the ribose ring causing steric interactions which in the anti conformation with x close to 180° (ap) are avoided. The anti conformation is therefore preferred and is the j only form observed in double-helical DNA and RNA. An exception is the left-handed Z-DNA with alternating purine/pyrimidine nucleotide sequence where the purines are in the syn conformation. 

In all the naturally occurring DNA and RNA double helices, the base pairs are of the Watson-Crick type A U(T) and O C. If DNA with the four nucleotides in random sequence [and not in alternating purine-pyrimidine sequence as in poly(dO-dC)] is exposed to different salt concentrations (and metal ions), it adopts two principal secondary structures A and B. 

Table 22.2. Sixteen configurations observed for water molecules in hydrates of organic molecules (carbohydrates, amino acids, peptides, purines, pyrimidines, nucleosides and nucleotides). First number refers to acceptor bonds, X—H -Ow. Second number refers to donor bonds OwH A. CD indicates chelated... 

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