The pentose sugar, phosphate group and organic base are joined, as a result of condensation reactions, to form a single nucleotide (mononucleotide). Two mononucleotides may, in turn, be joined as a result of a condensation reaction between the deoxyribose sugar, of one mononucleotide and the phosphate group of another. The bond formed between them is called a phosphodiester bond. The new structure is called a dinucleotide. The continued linking of mononucleotides in this way forms a long chain known as a polynucleotide. In addition to DNA and RNA, some other biologically important molecules contain nucleotides. For simplicity the various components of nucleotides are represented by symbols shown left.
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