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cytosine (sīˈtōsēnˌ), 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. Combined with the sugar ribose in glycosidic linkage, cytosine forms a derivative called cytidine (a nucleoside), which in turn can be phosphorylated with from one to three phosphoric acid groups, yielding the three nucleotides CMP (cytidine monophosphate), CDP (cytidine diphosphate), and CTP (cytidine triphosphate). Analogous nucleosides and nucleotides are formed from cytosine and deoxyribose. The nucleoside derivatives of cytosine perform important functions in cellular metabolism. CTP acts as a coenzyme in both carbohydrate and lipid metabolism; it can readily donate one of its phosphate groups to adenosine diphosphate (ADP) to form adenosine triphosphate (ATP), an extremely important intermediate in the transfer of chemical energy in living systems. CTP is the source of the cytidine found in ribonucleic acid (RNA) and deoxycytidine triphosphate (dCTP) is the source of the deoxycytidine in deoxyribonucleic acid (DNA). Thus cytosine is intimately involved in the preservation and transfer of genetic information.
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CDP(1) See continuous data protection.
(2) (Charging Downstream Port) See USB power.
(3) (Certificate in Data Processing) An earlier award for the successful completion of an examination in hardware, software, systems analysis, programming, management and accounting, offered by the ICCP. See ICCP.
(4) (Cisco Discovery Protocol) A protocol used by Cisco bridges and routers to inform each other of their existence. It sends frames over the data link layer (Ethernet, frame relay, ATM, etc.) to a multicast address. The content of the CDP message is addresses that SNMP messages can be sent to.
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