<P> 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 (- CH - OH) to produce nucleotides . Nucleotides are the molecular building - blocks of DNA and RNA . </P> <P> 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: </P> <Ul> <Li> in the lumen of the digestive system by nucleosidases into nucleobases and ribose or deoxyribose . </Li> </Ul> <Li> in the lumen of the digestive system by nucleosidases into nucleobases and ribose or deoxyribose . </Li>

Adenosine is a combination of what two compounds