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(no͞o`klēətīd', nyo͞o`–), organic substance that serves as a monomer in forming nucleic acidsnucleic acid,
any of a group of organic substances found in the chromosomes of living cells and viruses that play a central role in the storage and replication of hereditary information and in the expression of this information through protein synthesis.
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. Nucleotides consist of either a purinepurine,
type of organic base found in the nucleotides and nucleic acids of plant and animal tissue. The German chemist Emil Fischer did much of the basic work on purines and introduced the term into the chemical literature in the early 20th cent.
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 or a pyrimidinepyrimidine
, type of organic base found in certain coenzymes and in the nucleic acids of plant and animal tissue. The three major pyrimidines of almost universal distribution in living systems are cytosine, thymine, and uracil.
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 base, a riboseribose
, monosaccharide carbohydrate of universal distribution in living tissue, found in ribonucleic acid (RNA; see nucleic acid), free nucleotides, and various coenzymes.
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 or deoxyribose, and a phosphate group. Adenosine triphosphateadenosine triphosphate
(ATP) , organic compound composed of adenine, the sugar ribose, and three phosphate groups. ATP serves as the major energy source within the cell to drive a number of biological processes such as photosynthesis, muscle contraction, and the synthesis of
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 serves as the principle energy carrier for the cell's reactions. The most important nucleotides are those derived from the bases adenineadenine
, organic base of the purine family. Adenine combines with the sugar ribose to form adenosine, which in turn can be bonded with from one to three phosphoric acid units, yielding the three nucleotides adenosine monophosphate, adenosine diphosphate, and adenosine
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, guanineguanine
, organic base of the purine family. It was reported (1846) to be in the guano of birds; later (1879–84) it was established as one of the major constituents of nucleic acids.
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, cytosinecytosine
, organic base of the pyrimidine family. It was isolated from the nucleic acid of calf thymus tissue in 1894. A suggested structure for cytosine, published in 1903, was confirmed in the same year when that base was synthesized in the laboratory.
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, thyminethymine
, organic base of the pyrimidine family. Thymine was the first pyrimidine to be purified from a natural source, having been isolated from calf thymus and beef spleen in 1893–4.
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, and uraciluracil
, organic base of the pyrimidine family. It was isolated from herring sperm and also produced in a laboratory in 1900–1901. When combined with the sugar ribose in a glycosidic linkage, uracil forms a derivative called uridine (a nucleoside), which in turn can be
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A cellular constituent that is one of the building blocks of ribonucleic acids (RNA) and deoxyribonucleic acid (DNA). In biological systems, nucleotides are linked by enzymes in order to make long, chainlike polynucleotides of defined sequence. The order or sequence of the nucleotide units along a polynucleotide chain plays an important role in the storage and transfer of genetic information. Many nucleotides also perform other important functions in biological systems. Some, such as adenosine triphosphate (ATP), serve as energy sources that are used to fuel important biological reactions. Others, such as nicotinamide adenine dinucleotide (NAD) and coenzyme A (CoA), are important cofactors that are needed to complete a variety of enzymatic reactions. Cyclic nucleotides such as cyclic adenosine monophosphate (cAMP) are often used to regulate complex metabolic systems. Chemically modified nucleotides such as fluoro-deoxyridine monophosphate (Fl-dUMP) contain special chemical groups that are useful for inactivating the normal function of important enzymes. These and other such compounds are widely used as drugs and therapeutic agents to treat cancer and a variety of other serious illnesses. See Coenzyme, Cyclic nucleotides, Nicotinamide adenine dinucleotide (NAD)

Nucleotides are generally classified as either ribonucleotides or deoxyribonucleotides. Both classes consist of a phosphorylated pentose sugar that is linked via an N-glycosidic bond to a purine or pyrimidine base. The combination of the pentose sugar and the purine or pyrimidine base without the phosphate moiety is called a nucleoside. See Purine, Pyrimidine

Ribonucleosides contain the sugar d -ribose, whereas deoxyribonucleosides contain the sugar 2-deoxyribose. The four most common ribonucleosides are adenosine, guanosine, cytidine, and uridine. The purine ribonucleosides, adenosine and guanosine, contain the nitrogenous bases adenine and guanine, respectively. The pyrimidine ribonucleosides, cytidine and uridine, contain the bases cytosine and uracil, respectively. Similarly, the most common deoxyribonucleosides include deoxyadenosine, deoxyguanosine, deoxycytidine, and thymidine, which contains the pyrimidine base thymine. Phosphorylation of the ribonucleosides or deoxyribonucleosides yields the corresponding ribonucleotide or deoxyribonucleotide. See Deoxyribonucleic acid (DNA), Enzyme, Nucleic acid, Ribonucleic acid (RNA)


An ester of a nucleoside and phosphoric acid; the structural unit of a nucleic acid.
References in periodicals archive ?
We calculated the baseline reference value as the mean number of unique repeat lengths at each mononucleotide tract across a population of MSI-negative samples.
Detection of microsatellite instability in colorectal cancer using an alternative multiplex assay of quasi-monomorphic mononucleotide markers.
Nicotinamide mononucleotide, a key NAD(+) intermediate, treats the pathophysiology of diet- and age-induced diabetes in mice.
Hustad S, Ueland PM, Schneede J Quantification of riboflavin, flavin mononucleotide, and flavin adenine dinucleotide in human plasma by capillary electrophoresis and laser-induced fluorescence detection.
A 1997 National Cancer Institute (NCI) consensus panel recommended that MSI-H in colon cancer determined via PCR be defined as instability in at least 2 of 5 recommended markers (the mononucleotide markers BAT26 and BAT25 or the dinucleotide markers D5S346, D2S123, and D17S250), otherwise known as the Bethesda panel.
Evaluation of tumor microsatellite instability using five quasimonomorphic mononucleotide repeats and pentaplex PCR.
Recently the exclusive use of traditional (BAT25 and BAT26) and/or novel (CAT25, SEC63, NR-21, NR-22, NR-24, and NR-27) monomorphic mononucleotide repeat markers in various combinations has been successfully applied by some groups (6,8-13).
30) It consists of 2 mononucleotide repeats (BAT25, BAT26) and 3 dinucleotide repeats (D5S346, D2S123, D17S250).
The intensities of 5-methylcytosine and cytosine mononucleotide spots were measured with a PhosphorImager screen and by ImageQuant quantification (GE Healthcare Life Sciences).
MSI testing is generally performed with at least 5 microsatellite markers, generally mononucleotide or dinucleotide repeat markers.
The original panel of 5 microsatellite markers, 2 mononucleotide (BAT25 and BAT26) and 3 dinucleotide (D2S123, D5S346, and D17S250) sequences, (80,81) is based on a 1997 consensus recommendation by the National Cancer Institute, (80,81) also referred to as the "Bethesda panel.
2]) participates in redox reactions in 2 coenzyme forms, flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD) (1).