Also found in: Dictionary, Thesaurus, Medical, Acronyms, Wikipedia.


(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.
..... Click the link for more information.
. 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.
..... Click the link for more information.
 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.
..... Click the link for more information.
 base, a riboseribose
, monosaccharide carbohydrate of universal distribution in living tissue, found in ribonucleic acid (RNA; see nucleic acid), free nucleotides, and various coenzymes.
..... Click the link for more information.
 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
..... Click the link for more information.
 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
..... Click the link for more information.
, 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.
..... Click the link for more information.
, 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.
..... Click the link for more information.
, 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.
..... Click the link for more information.
, 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
..... Click the link for more information.


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 ?
Presences of the leading nucleotide manufacturer in the region coupled with increasing demand for nutraceuticals and health food industry is expected to increase demand for the product.
Combinations of three nucleotides in DNA, also sometimes called bases, specify particular amino acids.
Among the examined Alternaria species, the nucleotide differences between A.
the query nucleotide has a (non-empty) assistant factor.
To explore the relationship between environmental exposure and genetic susceptibility in the etiology of common diseases, the Environmental Genome Project is scanning environmental response genes involved in DNA repair, cell cycle control, apoptosis, drug metabolism, and other pathways for single nucleotide polymorphisms (SNPs).
Chapter Four Nucleotide Development Policy and Plan
The second eDNA library was amplified by PCR with specially designed primer sets in which 6 nucleotides composed of CC (HaeIII-digested sequence) and 4 variable nucleotides were added to the 3' end of the adaptor sequence (Figure 2).
Over 35 grants have been awarded for research including nucleotide selectivity of error prone RNA viral polymerases, PCR primer design for undergraduate teaching and research, CleanAmp (TM) Primers for detection of mRNA expression and DNA repair studies of cross-linked DNA.
A clear resolution of lineage IA clades was not obtained from the nucleotide sequences of the C/preM fragments.
For example, Cd(II), Cu(II), Co(II), and Ni(II) inhibit (at concentrations [greater than or equal to] 200 [micro]M) the in vitro DNA-binding activity of the human xeroderma pigmentosum group A protein, a critical damage recognition factor in nucleotide excision repair (Asmuss et al.
To create the particles, chemists Bruce Eaton and Dan Feldheim of North Carolina State University in Raleigh synthesized trillions of RNA fragments, each with its own sequence of building blocks called nucleotides.
Antonin Holy, IOCB, will be the first to hold the position of Distinguished Chair and will continue to lead research efforts in nucleoside and nucleotide drug discovery.