Pyrimidine Base

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Pyrimidine Base


(also called pyrimidine), any of a group of naturally occurring compounds that are derivatives of the heterocyclic nitrogenous base pyrimidine. Pyrimidine bases, which are components of nucleic acids, are very important in metabolism. Nucleic acids contain large amounts of the pyrimidine bases cytosine, or 2-hydroxy-6-aminopyrimidine; uracil, or 2,6-dihydroxypyrimidine; and thymine, or 5-methyluracil. They also contain smaller amounts of minor bases, for example, 5-methylcytosine. The number of minor bases in transfer ribonucleic acid (RNA) is especially high.

The combination of certain carbohydrates with purine or pyrimidine bases is called a nucleoside. The nucleosides in RNA consist of pyrimidine bases bound by a glycosidic linkage to the carbohydrate ribose, while those in deoxyribonucleic acids (DNA) consist of pyrimidine bases bound to deoxyribose. Nucleotides, which are the monophosphate esters of nucleosides, are the basic structural units of nucleic acids. In DNA, the pyrimidine-base content equals that of the purine bases, while RNA usually contains somewhat fewer pyrimidine bases than purine bases (the relative amount of nitrogenous bases in a nucleic acid is described by the Chargaff rule). As a result of their capacity to interact specifically with purine bases according to the complementarity principle, pyrimidine bases participate in the coding and transfer of the genetic information that is contained in nucleic acids.

Nucleotides that contain pyrimidine bases are also important in metabolism, for example, uridine diphosphate in carbohydrate metabolism and cytidine diphosphate in lecithin metabolism. Pyrimidine bases are synthesized in the cell from derivatives of orotic acid.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
The latest reactions "provide a plausible route to the pyrimidine bases required in a [primitive] RNA world," the two state.
Surprisingly, the analysis of 5,6-dihydrouridine in urine with the chromatographic and MS conditions as described for the pyrimidine bases and their degradation products showed that the presence of this compound interferes with the detection of 5,6-dihydrouracil.
Nevertheless, the specific transition of m/z 132 [right arrow] 115 for 5,6-dihydrouracil allows the identification of all pyrimidine bases and their degradation products within one analytical run of 15 min.
Since UV-B is known to affect adjacent pyrimidine bases on the DNA by linking them to form dimers, Harlow et al.
Catabolism of the pyrimidine bases thymine and uracil consists of three consecutive steps: (a) thymine and uracil are catabolized by dihydropyrimidine dehydrogenase (DPD; EC [3] to dihydrothymine (DHT) and dihydrouracil (DHU), respectively; (b) DHT is converted to N-carbamyl-[beta]-aminoisobutyric acid (N-C-[beta]-AlB) and DHU to N-carbamyl-[beta]-alanine (N-C-(3-Ala) by dihydropyrimidinase (DHP, EC; and (c) ([beta]-ureidopropionase (([beta]-UP; EC catalyzes the last step in pyrimidine degradation by converting N-C-[beta]-AIB to ([beta]-aminoisobutyric acid and N-C-[beta]-Ala to ([beta]-alanine.
Patients with a DHP deficiency accumulate DHT and DHU and exhibit slightly increased concentrations of the pyrimidine bases. In the only [beta]-UP-deficient patient diagnosed to date, the N-carbamyl compounds were increased in urine.
Dihydropyrimidine dehydrogenase (DPD; [1] EC is the initial and rate-limiting enzyme in the catabolism of the pyrimidine bases, and it catalyzes the reduction of thymine and uracil to 5,6-dihydrothymine and 5,6-dihydrouracil, respectively.
[4-[sup.14]C]Thymine was catabolized by human liver to radiolabeled dihydrothymine, N-carbamyl-[beta]-aminoisobutyric acid, and [beta]-aminoisobutyric acid, showing the presence of all three active enzymes--DPD, dihydropyrimidinase, and [beta]-ureidopropionase--of the catabolic pathway of the pyrimidine bases.
Separation of purine and pyrimidine bases and of nucleotides by anion exchange.
Dihydropyrimidine dehydrogenase is the initial enzymatic step in the degradative pathway of the pyrimidine bases uracil and thymine (Fig.