Pyrimidine Nucleotides and Nucleosides

Both DNA and RNA contain two major purine bases, adenine (A) and guanine (G), and two major pyrimidines. In both DNA and RNA one of the pyrimidines is cytosine (C), but the second major pyrimidine is not the same in both it is thymine (T) in DNA and uracil (U) in RNA Only rarely does thymine occur in RNA or uracil in DNA The structures of the five major bases are shown in Figure 8-2, and the nomenclature of their corresponding nucleotides and nucleosides is summarized in Table 8-1. 

The pyrimidine bases, their derivatives, nucleotides, and nucleosides have been extensively studied by NMR techniques including proton magnetic resonance (PMR), carbon-13, nitrogen-15, and fluorine-19 magnetic resonances as well as nitrogen-14 nuclear qxiadrupole resonance (14N NQR). 

It was concluded39 from these studies that the two nucleotides obtained by enzymic hydrolysis of the deoxyribonucleic acid of T2 bacteriophage are 2-deoxy-5 -(hydroxymethyl)cytidylic acid and a glucose derivative thereof. It was also concluded that the glucose residue is affixed to the pyrimidine portion of the nucleotide and nucleoside of 5-(hydroxymethyl)-cytosine and, on the basis of the near identity of the spectra of the two nucleotides of 5-(hydroxymethyl)cytosine, it was suggested that the hexose is attached to the hydroxymethyl group of the pyrimidine. 

Understand the properties of purine and pyrimidine bases and nucleosides, and nucleotides with varying amounts of phosphate. Recognize the structures of the various xanthines, cyclic nucleotides, uric acid, and bases found in nucleic acids. 

As neutron diffraction and more accurate X-ray crystal structure analyses have become available, it is clear that this configuration 1 is quite common in the crystal structures of many biological small molecules. Surveys of the peptide NH 0=C hydrogen bond [56] and hydrogen bonds in carbohydrates [57-59], amino acids [60], purines and pyrimidines [61] and nucleosides and nucleotides [62] indicate that between 25% and 40% of the bonds in a sample of structures may be of this type. 

Various aspects of bacterial nucleotides and nucleosides have been included in a number of recent reviews on such subjects as purine and pyrimidine synthesis, coenzymes, and carbohydrate polymers. ... 

Many studies on the spectroscopic properties in the near and far ultraviolet region of cytosine, uracil, thymine, their derivatives, nucleotides and nucleosides have been made in recent years. DeVoe and Tinoco, for instance, following previous efforts by other investigators, have extended to short wavelengths ( 186 nm) the measurements of the absorption spectra of the four deoxyribonucleo-sides of DNA. Marshall and Walker have analyzed the UV spectra of 2,4-disubstituted pyrimidines, and Shugar and Fox ° examined the spectra of the p3n imidine bases of the nucleic acids and their... 

Two Nitrogen Atoms (it is self-sub divided into 1,2-Heterocycles, 1,3-Heterocycles Monocyclic Pyrimidines and Hydropyrimidines Except Pyrimidine Nucleoside Bases and Nucleosides, Annulated Pyrimidines Except Purines, Pteridines, and Flavins, Pyrimidine Nucleoside Bases and Purines, Nucleotides and Nucleosides, Nucleic Acids, Pyrazines, and Hydropyrazines). 

Although certain purine and pyrimidine nucleosides are adaptable to mass spectrometiic studies without prior substitution, the application of this technique to nucleotides and nucleosides containing more polar heterocycles (guanosine, cytidine) has been precluded because of their lower volatility. Conversion of these substances into their trimethylsilyl derivatives affords sufficiently volatile compounds which are conveniently studied by mass spectrometry. From a study of trimethylsilyl ethers of nucleosides it should be possible to determine the molecular weight or elemental composition from the M and M-15 peaks, in addition to other... 

Figure 29-3. Structure of tRNA. Left sequence and projection of the conformation. The numbering corresponds to the phenyl alanine specific tRN A of yeast. A, Adenyl nucleoside C, cytosyl nucleoside G, guanidyl nucleoside T, thymidyl nucleoside U, uridyl nucleoside. In the case of the pseudouridyl residue the base is joined to the sugar via the C Pu is a purine nucleotide, Py is a pyrimidine nucleotide, and H is what is known as a hypermodified purine nucleotide. The other positions can be taken by any desired nucleotide, but must be complementary in the case of the hydrogen bonds signified by —. w, Wobble base. Right Spatial structure.

Ncuhard J. Utilisation of prefoimed pyrimidine bases and nucleosides. Munch-Petersen A, ed. Metabolism of Nucleotides, Nucleosides, and Nucleobases in Microorganisms. London Academic Press, 1983 95-148. 

ECTEOLA is named for the epichlorohydrin and triethanolamine groups which are combined with cellulose. DEAE-cellulose and ECTEOLA-cellulose layers have about the same ability to resolve nucleic acid derivatives. ECTEOLA is especially useful for nucleic acids, nucleotides and nucleosides as an anion exchanger. Its strength also lies in its rapid separation of pyrimidines from purines. 

Heterocyclic substances other than purines and pyrimidines are found in nucleotides and nucleosides. Some examples are nicotinamide in diphos-phopyridine nucleotide (DPN) and triphosphopyridine nucleotide (TPN), 5,6-dimethyl benzimidazole in vitamin Bu, and imidazoleacetic acid in imidazoleacetic riboside (S). 

The nucleic acids DNA (deoxyribonucleic acid) and RNA (ribonucleic acid) are biological polymers that act as chemical carriers of an organism s genetic information. Enzyme-catalyzed hydrolysis of nucleic acids yields nucleotides, the monomer units from which RNA and DNA are constructed. Further enzyme-catalyzed hydrolysis of the nucleotides yields nucleosides plus phosphate. Nucleosides, in turn, consist of a purine or pyrimidine base linked to Cl of an aldopentose sugar—ribose in RNA and 2-deoxyribose in DNA. The nucleotides are joined by phosphate links between the 5 phosphate of one nucleotide and the 3 hydroxyl on the sugar of another nucleotide. 

While mammahan cells reutilize few free pyrimidines, salvage reactions convert the ribonucleosides uridine and cytidine and the deoxyribonucleosides thymidine and deoxycytidine to their respective nucleotides. ATP-dependent phosphoryltransferases (kinases) catalyze the phosphorylation of the nucleoside diphosphates 2 "-de-oxycytidine, 2 -deoxyguanosine, and 2 -deoxyadenosine to their corresponding nucleoside triphosphates. In addition, orotate phosphoribosyltransferase (reaction 5, Figure 34-7), an enzyme of pyrimidine nucleotide synthesis, salvages orotic acid by converting it to orotidine monophosphate (OMP). 

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