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( Nucleotide)
Nucleotides are organic compounds that consist of three joined structures a nitrogenous base, a sugar, and a phosphate group. The most common nucleotides can be divided into two groups (purines and pyrimidines) based on the structure of the nitrogenous base. The joined sugar is either ribose or deoxyribose. Nucleotides are the structural units of RNA and DNA. They also serve as important cofactors in cellular signaling and metabolism. These cofactors include CoA, flavin adenine dinucleotide, flavin mononucleotide, adenosine triphosphate and nicotinamide adenine dinucleotide phosphate. A nucleotide is composed of a ring of nitrogen, carbon and oxygen atoms, a five carbon sugar (together referred to as a nucleoside) and one phosphate group. Nucleotides can be synthesized through a variety of methods both in vitro and in vivo. This can involve salvage synthesis (the re-use of parts of nucleotides in resynthesizing new nucleotides through breakdown and synthesis reactions in order to exchange useful parts), or the use of protecting groups in a laboratory. In the latter case, a purified nucleoside or nucleobase is protected to create a phosphoramidite, and can be used to obtain analogues not present in nature and/or to create an oligonucleotide. The first step of nucleotide synthesis is the formation of a nucleoside (the nitrogenous base joined to a sugar). The sugar involved in the synthesis and structure of a nucleotide may be either ribose or deoxyribose; in the latter case, the prefix 'deoxy' may be added before the name of the nucleoside in all cases except Uracil. A functional group of phosphate is then esterified to the sugar, creating a nucleotide. The phosphate group may consist of one, two, or three phosphates, forming monophosphates, diphosphates, or triphosphates, respectively.
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