Difference between revisions of "Nucleoside" - New World Encyclopedia

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Nucleosides are structural subunits of nucleic acids, the macromolecules that convey genetic information in living cells. They consist of a nitrogen-containing base bonded to a five-carbon (pentose) sugar.

Nucleosides are the biochemical precursors of nucleotides, the molecular building blocks of the nucleic acids DNA and RNA. Nucleotides are formed by the addition of one or more phosphate groups to the nucleoside.

Some nucleosides have important clinical applications; for example, puromycin and certain other antibiotics are nucleosides produced by molds or fungi.

Drug researchers have also drawn on an understanding of the biochemistry of naturally occurring nucleosides to build synthetic molecules called nucleoside analogs. One class of antiretroviral drugs is called nucleoside analog reverse transcriptase inhibitors (NARTIs or NRTIs). NRTIs inhibit the activity of reverse transcriptase, a viral DNA polymerase enzyme needed by HIV in order to reproduce. When HIV infects a cell, reverse transcriptase copies the single-stranded RNA genome of the virus into a double-stranded viral DNA molecule. The viral DNA is then integrated into the host’s chromosomal DNA, which allows the host to reproduce the virus. NRTIs block reverse transcriptase's enzymatic function, disrupting the synthesis of the double-stranded viral DNA and thus preventing HIV from multiplying. In order to be incorporated into the viral DNA, NRTIs must be activated in the cell by the addition of three phosphate groups to form NRTI triphosphates.

The chemical components of nucleosides

The nitrogen-containing base of a nucleoside (also called the nucleobase) is typically a derivative of either purine or pyrimidine, which are heterocyclic compounds (organic compounds that contain a ring structure that has, in addition to carbon, such atoms as sulfur, oxygen, or nitrogen). The most common bases in nucleosides are:

The purines adenine and guanine;
The pyrimidines cytosine, thymine, and uracil.

The sugar component is either deoxyribose or ribose. (“Deoxy” simply indicates that the sugar lacks an oxygen atom present in ribose, the parent compound.)

Below is a table listing the common bases and their corresponding nucleosides:

Nitrogenous base	Nucleoside	Deoxynucleoside
Adenine	Adenosine A	Deoxyadenosine dA
Guanine	Guanosine G	Deoxyguanosine dG
Thymine	5-Methyluridine m⁵U	Deoxythymidine dT
Uracil	Uridine U	Deoxyuridine dU
Cytosine	Cytidine C	Deoxycytidine dC

Nucleosides are nucleotide precursors

A nucleotide is a phosphate ester of a nucleoside. In chemistry, esters are organic compounds in which an organic group replaces a hydrogen atom or multiple hydrogens in an oxygen acid. Here, the hydroxyl group of the nucleoside, attached to carbon atom 5 of the sugar unit, is replaced by one or more phosphate groups.

Nucleotides are named according to the nucleoside that corresponds to the base. For example, the nucleotide adenosine triphosphate (ATP) is a derivative of the nucleoside adenosine.

The breakdown of nucleosides

There is a continuous turnover of nucleotides in the cell. Nucleosides are derived in the second step of nucleic acid degradation when a class of enzymes called nucleotidases split nucleotides into their component nucleosides and phosphate groups. The nucleosides, in turn, are subsequently broken down:

In the lumen of the digestive system by nucleosidases into nitrogenous bases and ribose (or deoxyribose).
Inside the cell by nucleoside phosphorylases into nitrogenous bases and ribose-1-phosphate (or deoxyribose-1-phosphate).

References
ISBN links support NWE through referral fees

Stryer, L. 1995. Biochemistry, 4th edition. New York, NY: W.H. Freeman.

Nucleic acids edit
Nucleobases: Adenine - Thymine - Uracil - Guanine - Cytosine - Purine - Pyrimidine
Nucleosides: Adenosine - Uridine - Guanosine - Cytidine - Deoxyadenosine - Thymidine - Deoxyguanosine - Deoxycytidine
Nucleotides: AMP - UMP - GMP - CMP - ADP - UDP - GDP - CDP - ATP - UTP - GTP - CTP - cAMP - cGMP
Deoxynucleotides: dAMP - dTMP - dUMP - dGMP - dCMP - dADP - dTDP - dUDP - dGDP - dCDP - dATP - dTTP - dUTP - dGTP - dCTP
Nucleic acids: DNA - RNA - LNA - PNA - mRNA - ncRNA - miRNA - rRNA - siRNA - tRNA - mtDNA - Oligonucleotide

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@@ Line 2: / Line 2: @@
 '''Nucleosides''' are structural subunits of [[nucleic acid]]s, the macromolecules that convey genetic information in living cells. They consist of a nitrogen-containing base bonded to a five-carbon ([[pentose]]) sugar.
-Nucleosides are the biochemical precursors of [[nucleotide]]s, the molecular building blocks of [[DNA]] and [[RNA]]. Nucleotides are formed by the addition of one or more phosphate groups to the nucleoside.
+Nucleosides are the biochemical precursors of [[nucleotide]]s, the molecular building blocks of the nucleic acids [[DNA]] and [[RNA]]. Nucleotides are formed by the addition of one or more phosphate groups to the nucleoside.
 Some nucleosides have important clinical applications; for example, [[puromycin]] and certain other [[antibiotic]]s are nucleosides produced by [[mold]]s or [[fungi]].
-Drug researchers have also drawn on an understanding of the biochemistry of naturally occurring nucleosides to build synthetic molecules called [[nucleoside analog]]s. One class of antiretroviral drugs is called ''Nucleoside analog reverse transcriptase inhibitors (NARTIs or NRTIs)''. NRTIs inhibit the activity of [[reverse transcriptase]], a viral DNA polymerase [[enzyme]] needed by HIV in order to reproduce. When HIV infects a cell, reverse transcriptase copies the single-stranded RNA genome of the virus into a double-stranded viral DNA molecule. The viral DNA is then integrated into the host’s chromosomal DNA, which allows the host to reproduce the virus. NRTIs block reverse transcriptase's enzymatic function, disrupting the synthesis of the double-stranded viral DNA and thus preventing HIV from multiplying. In order to be incorporated into the viral DNA, NRTIs must be activated in the cell by the addition of three phosphate groups to form NRTI triphosphates.
+Drug researchers have also drawn on an understanding of the biochemistry of naturally occurring nucleosides to build synthetic molecules called [[nucleoside analog]]s. One class of antiretroviral drugs is called ''nucleoside analog reverse transcriptase inhibitors (NARTIs or NRTIs)''. NRTIs inhibit the activity of [[reverse transcriptase]], a viral DNA polymerase [[enzyme]] needed by HIV in order to reproduce. When HIV infects a cell, reverse transcriptase copies the single-stranded RNA genome of the virus into a double-stranded viral DNA molecule. The viral DNA is then integrated into the host’s chromosomal DNA, which allows the host to reproduce the virus. NRTIs block reverse transcriptase's enzymatic function, disrupting the synthesis of the double-stranded viral DNA and thus preventing HIV from multiplying. In order to be incorporated into the viral DNA, NRTIs must be activated in the cell by the addition of three phosphate groups to form NRTI triphosphates.
 == The chemical components of nucleosides ==
@@ Line 51: / Line 51: @@
 A ''nucleotide'' is a phosphate ester of a nucleoside. In chemistry, ''esters'' are organic compounds in which an organic group replaces a hydrogen atom or multiple hydrogens in an oxygen acid. Here, the hydroxyl group of the nucleoside, attached to carbon atom 5 of the sugar unit, is replaced by one or more phosphate groups.
-Nucleotides are named according to the nucleoside corresponding to the base. For example, the nucleotide [[adenosine triphosphate (ATP)]] is a derivative of the nucleoside ''adenosine'' that contains three phosphate groups.
+Nucleotides are named according to the nucleoside that corresponds to the base. For example, the nucleotide [[adenosine triphosphate (ATP)]] is a derivative of the nucleoside ''adenosine''.
 == The breakdown of nucleosides ==