Pyrimidine nitrogenous base

The genetic code is composed of four letters —two pyrimidine nitrogenous bases, thymine and cytosine, and two purine bases, guanine and adenine—which can be regarded functionally as arranged in codons (or triplets). Each codon consists of a combination of three letters therefore, 43 (64) different codons are possible. Sixty-one codons code for specific amino acids (three produce stop signals), and as only 20 different amino acids are used to make proteins, one amino acid can be specified by more than one codon. 

Pyrimidines nitrogenous bases (cytosine and thymine) found in nucleotides. 

DNA contains all the cell s hereditary information. Upon cell division, each new cell receives a complete copy of its parents DNA. The sequence of the subunit nucleotides along the polymer chain holds this information. Nucleotides are made up of deoxyribose, phosphoric acid, and a purine or pyrimidine nitrogenous base. RNA is a polymer of ribose-containing nucleotides. Of the nitrogenous bases, adenine, guanine, and cytosine are... 

The nucleophilicity of amine nitrogens is also differentiated by their environments. In 2,4,5,6-tetraaminopyrimidine the most basic 3-amino group can be selectively converted to a Schiff base. It is meta to both pyrimidine nitrogens and does not form a tautomeric imine as do the ortho- and /xira-amino groups. This factor is the basis of the commercial synthesis of triamterene. 

In such names, numerals will refer to carbon atoms of the sugar moiety, and primed numerals to the positions on the nitrogenous base compare Ref. 1, pp. 200 and 208. Pyrimidines and purines are numbered by the Chem. Abstracts system. 

Nitrogenous base plus sugar moiety are called nucleosides. Ribonucleic acids (RNA) resemble DNA in that nucleoside monophosphates are joined through phosphodiester bonds. RNAs differ in that the sugars are p-D-ribose units and the pyrimidine uracil is found in place of thymine. Molecular structures and nomenclature for nitrogenous bases, nucleosides, and nucleotides are delineated in Table 2.2. 

Nucleotides are the phosphoric acid ester of nucleoside, while nucleosides are compounds in which nitrogenous bases (purines and pyrimidines) are conjugated to the pentose sugar (ribose or deoxyribose) by a b-glycosidic linkage. AMP, ATP, ADP, GMP, CMP, UMP are the examples of mononucleotides. 

The prebiotic synthesis of pyrimidines is based on cyanoacetylene, which is obtained in good yields by sparking mixtures of methane and nitrogen and by the... 

DNA, a constituent of the cell nucleus, consists of two strands of polynucleotides that are coiled to form a double helix. The strands are held together by H-bonding between the nitrogen bases. The pyrimidines always form H-bonds with a specific purine i.e., cytosine with guanine and thymine with adenine. However, in RNA the pairing is between uracil and adenine. 

Conformational inversions in the field of ketonucleosides were established by n.m.r.-spectral analysis. It has been reported30,32 that the introduction of a carbonyl group at C-4 of the sugar moiety of L-rhamnosyl-purines and -pyrimidines led to ketonucleosides possessing an axially attached nitrogenous base. Such unusual positions of the base have been observed in the case of a glycosyltheophylline,61 and for some derivatives of a rhamnosyl-5-fluorouracil.48... 

Nucleotides are composed of a nitrogenous base, a pentose monosaccharide, and one, two, or three phosphate groups. The nitrogen-containing bases belong to two families of compounds the purines and the pyrimidines. 

The structural components of nucleic acids. Nucleic acids are long linear polymers of nucleotides, called polynucleotides, (a) The nucleotide consists of a five-carbon sugar (ribose in RNA or deoxyribose in DNA) covalently linked at the 5 carbon to a phosphate, and at the 1 carbon to a nitrogenous base. (b) Nucleotides are distinguished by the types of bases they contain. These are either of the two-ring purine type or of the one-ring pyrimidine type. 

Nitrogenous base. An aromatic nitrogen-containing molecule with basic properties. Such bases include purines and pyrimidines. 

Two important reactions of arene oxides in animal tissue are (1) detoxification and (2) formation of conjugates of arene oxides with purine pyrimidine bases of DNA. For both of these reactions to take place, the arene oxide should have a certain intrinsic stability to survive an aromatization reaction. Reaction with the thiolate bond of glutathione is responsible for detoxification, whereas the extent of involvement of arene oxides in the nucleophilic reactions with nonpolarized nitrogen bases of DNA is directly related to their carcinogenic activity. 

A nitrogenous base of either purine or pyrimidine derivation, covalently attached to the l -carbon atom of the sugar by an N-glycosylic bond as shown in Figure 7.1... 

One obvious problem with our choice of model sugar is that Cl is connected to a methoxy group in place of the nitrogenous base that would be found in nucleic acids. This clearly introduces a bias at the HI position that needs to be corrected for. Based on results discussed below, we have added 0.32 ppm from the reference shift for HI in Table 1 for pyrimidines, and have subtracted 0.20 ppm for purines. This difference of 0.52 ppm in HI shift between purines and pyrimidines is close to the value of 0.44 ppm extracted from an empirical DNA database (7). 

The purines are an important class of heterocycles in which an imidazole ring is fused to a pyrimidine ring. Uric acid (the main product of nitrogen metabolism in birds and reptiles), caffeine (present in coffee), and adenine and guanine (nitrogen bases present in the nucleic acids DNA and RNA) are examples of naturally occurring purines. 

Identification of the nitrogenous bases (aglycons) of pyrimidine nucleosides began at the turn of the century, when Kossel and Neumann18 isolated thymine (5-methyluracil) from nucleic acid and showed this pyrimidine to be identical with the nucleosin previously described by Miescher.19 The isolation of cytosine20 [4-amino-2()//)-pyrimidinone] and uracil21 [2,4(1, 3 )-pyrimidinedione] from the nucleic acids came shortly there-... 

DNA is composed of three chemical functions A deoxyribose (a pentose, i.e., a sugar with five carbons), organic (nitrogenous) bases (pyrimidines cytosine and thymine purines adenine and guanine), and a phosphoric acid. 

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