Nucleic acid components pyrimidines

The 8-aza analogs of purine bases were the first to be studied among all the aza analogs of nucleic acid bases (as early as 1945). Before that time the chemistry of these substances had not been treated in detail from any aspect. Thus the entire chemistry of the u-triazolo [4,5-d]pyrimidines was developed only in connection with the study of antimetabolites of nucleic acid components. Therefore all the papers involved are largely of preparative character and only rarely discuss. theoretical points. 

The major intermediates in the biosynthesis of nucleic acid components are the mononucleotides uridine monophosphate (UMP) in the pyrimidine series and inosine monophosphate (IMP, base hypoxanthine) in the purines. The synthetic pathways for pyrimidines and purines are fundamentally different. For the pyrimidines, the pyrimidine ring is first constructed and then linked to ribose 5 -phosphate to form a nucleotide. By contrast, synthesis of the purines starts directly from ribose 5 -phosphate. The ring is then built up step by step on this carrier molecule. 

Guanine is a preferential DNA target to several oxidants it shows the lowest ionization potential among the different purine and pyrimidine nucleobases and it is the only nucleic acid component that exhibits significant reactivity toward singlet oxygen ( O2) at neutral pH. ... 

Becker RS, Kogan G (1980) Photophysical properties of nucleic acid components. 1. The pyrimidines Thymine, uracil, N,N-dimethyl derivatives, and thymidine. Photochemistry and Photobiology 31 5-13. 

Jeffrey GA (1989) Hydrogen bonding in crystal structures of nucleic acid components purines, pyrimidines, nucleosides and nucleotides. In Saenger W (ed), Landolt-BOrnstein. Numerical Data and Functional Relationships in Science and Technology. New Series, Group VII, Vol. Ib. Springer, Berlin, pp 277-348... 

Frey MN, Koetzle TF, Lehmann MS, Hamilton WC (1973) Predsion neutron diffraction structure determination of protein and nucleic acid components. XII. A study of hydrogen bonding in the purine-pyrimidine base pair 9-methyladenine and 1-methylthymine. J Chem Phys 59 915-924... 

In addition to major nucleosides and bases, modified nucleosides and bases have also been isolated from tRNA hydrolysates and in physiological fluids of man. Unlike the major nucleic acid components, the methylated or otherwise structurally altered purine and pyrimidine compounds are not recycled in the salvage pathways but are excreted. It has been suggested that the measurement of these modified compounds may provide an indicator of the rate of tRNA metabolism. Furthermore, the altered patterns of excretion for these compounds may be used as biomarkers for the detection of disease states and aberrations in metabolic pathways. 

Purine and pyrimidine analogues of nucleic acid components 84MI5. Pyrimidine antibiotics, polyoxines 79H(13)333. 

Since the reviews by Tipson < > and Barker < > on the chemistry of the nucleic acids, two Chapters have appeared in these Volumes on the chemistry of nucleic acid components, namely, the pyrimidine and purine ... 

Pyrimidine Nucleic acid component cytosine (4-amino-2-hydroxypyrimidine), uracil (2,4-dihydroxypyrimidine) thymine (5-methyluracil)... 

Among nucleic acid components purine and pyrimidine bases are electroactive deoxyribose and ribose in nucleosides and nucleotides as well as phosphate groups are inactive at most types of electrodes. 

Table 1 Abilities of (A) nucleic acid components and (B) some other purine and pyrimidine derivatives to form sparingly soluble compounds with the electrode mercury ...

N.a. are polymers with Af, between 20,000 and about 10 . They contain three structural components the purine and pyrimidine bases, a pentose (either d-ribose in RNA or 2-deoxy-D-ribose in DNA) and es-terified phosphate. The five major bases are uracil (RNA only), thymine (DNA only), adenine, guanine and cytosine (RNA and DNA) in addition, there are over Rare nucleic acid components (see) which occur in various N.a. These rare components are formed by modification of existing structures within the N.a., e.g. by methylation, hydrogenation or rearrangement of normal bases. 

Polynucleotide thioHransferases thiolases catalysing the specific thiolation of purine and pyrimidine bases in the synthesis of Rare nucleic acid components (see). 

Ribosylthymine, 2 -hydroxythymidtnt, ribothy-midine 5-methyluridine, a pyrimidine derivative, and a Rare nucleic acid component (see) found in tRNA. See Pyrimidine biosynthesis. Thymidine phosphates. 

The most important derivatives of pyrimidines and purines are nucleosides Nucleosides are N glycosides m which a pyrimidine or purine nitrogen is bonded to the anomeric carbon of a carbohydrate The nucleosides listed m Table 28 2 are the mam building blocks of nucleic acids In RNA the carbohydrate component is d ribofuranose m DNA It IS 2 deoxy d ribofuranose... 

Table 28 2 doesn t include all of the nucleoside components of nucleic acids The presence of methyl groups on pyrimidine and purine rings is a common and often important variation on the general theme... 

As is well-known, nucleic acids consist of a polymeric chain of monotonously reiterating molecules of phosphoric acid and a sugar. In ribonucleic acid, the sugar component is represented by n-ribose, in deoxyribonucleic acid by D-2-deoxyribose. To this chain pyrimidine and purine derivatives are bound at the sugar moieties, these derivatives being conventionally, even if inaccurately, termed as pyrimidine and purine bases. The bases in question are uracil (in ribonucleic acids) or thymine (in deoxyribonucleic acids), cytosine, adenine, guanine, in some cases 5-methylcytosine and 5-hydroxymethylcyto-sine. In addition to these, a number of the so-called odd bases occurring in small amounts in some ribonucleic acid fractions have been isolated. 

For various reasons, the generalizations mentioned above must be regarded as strictly provisional. Analyses utilizing formic acid indicate the presence of more than one phosphorus atom per purine or pyrimidine residue. This discrepancy, it is pointed out, could equally well result from an apparent deficiency of bases, due to error in the analytical technique.160 It is also necessary to consider that some nucleic acids are now known to contain more bases than was previously realized. Thus, 5-(hydroxymethyl)-cytosine is present in various viruses,181-182 and 5-methylcytosine occurs in various animal and plant deoxyribonucleic acids but is absent from those of microbial origin.17-160-1M- 184- 186 Certain microbial deoxyribonucleic acids also contain 6-methylaminopurine.186a Various bacteriophage deoxyribonucleic acids have been found to contain a component which is believed to consist of a D-glucoside186b of 5 -(hydroxymethyl)cytidylic acid. 

Those nucleosides found in the nucleic acids DNA and RNA involve the joining of ribose of deoxyribose to a purine or a pyrimidine base. One such nucleoside is adenosine, in which a nitrogen of adenine is linked to carbon 1 of the pentose, ribose. In this form it is a component of RNA but as a phosphory-lated derivative of adenosine (e.g. ATP), which is a high energy compound, it fulfils an important role in metabolism. The dinucleotides NAD and NADP are two cofactors necessary for many enzymic transformations and these also contain /V-glycosides of ribose phosphate. Other important nucleosides are found... 

The bases that occur in nucleic acids are aromatic heterocyclic compounds derived from either pyrimidine or purine. Five of these bases are the main components of nucleic acids in all living creatures. The purine bases adenine (abbreviation Ade, not A ) and guanine (Gua) and the pyrimidine base cytosine (Cyt) are present in both RNA and DNA. In contrast, uracil (Ura) is only found in RNA. In DNA, uracil is replaced by thymine (Thy), the 5-methyl derivative of uracil. 5-methylcyto-sine also occurs in small amounts in the DNA of the higher animals. A large number of other modified bases occur in tRNA (see p. 82) and in other types of RNA. 

Nucleic acids are broken down into their components by nucleases from the pancreas and small intestine (ribonucleases and deoxyribonucleases). Further breakdown yields the nucleobases (purine and pyrimidine derivatives), pentoses (ribose and deoxyribose). 

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