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Nucleosides are glycosylamines that can be thought of as nucleotides without a phosphate group. A nucleoside consists simply of a nucleobase (also termed a nitrogenous base) and a 5-carbon sugar (either ribose or deoxyribose), whereas a nucleotide is composed of a nucleobase, a five-carbon sugar, and one or more phosphate groups. In a nucleoside, the base is bound to either ribose or deoxyribose via a beta-glycosidic linkage. Examples of nucleosides include cytidine, uridine, adenosine, guanosine, thymidine and inosine. == Biological function == While a nucleoside is a nucleobase linked to a sugar, a nucleotide is composed of a nucleoside ''and'' one or more phosphate groups. Thus, nucleosides can be phosphorylated by specific kinases in the cell on the sugar's primary alcohol group (-CH2-OH) to produce nucleotides. Nucleotides are the molecular building-blocks of DNA and RNA. Nucleosides can be produced by de novo synthesis pathways, in particular in the liver, but they are more abundantly supplied via ingestion and digestion of nucleic acids in the diet, whereby nucleotidases break down ''nucleotides'' (such as the thymidine monophosphate) into ''nucleosides'' (such as thymidine) and phosphate. The nucleosides, in turn, are subsequently broken down: * in the lumen of the digestive system by nucleosidases into nucleobases and ribose or deoxyribose. In addition, nucleotides can be broken down: * inside the cell into nitrogenous bases, and ribose-1-phosphate or deoxyribose-1-phosphate. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Nucleoside」の詳細全文を読む スポンサード リンク
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