Formation of Dinucleotide and Polynucleotide

A nucleoside is the combination of a nitrogenous base and a pentose sugar alone (for example, adenosine = adenine + ribose, or guanosine = guanine + ribose). A nucleotide is formed when a phosphoric acid (phosphate) group is additionally attached to a nucleoside (for example, adenylic acid = adenosine + phosphoric acid). The nitrogenous base itself is a heterocyclic (ring-containing) compound that is either a purine (a two-ring structure - adenine and guanine are the two purines) or a pyrimidine (a one-ring structure - cytosine, thymine and uracil are the three pyrimidines). A nitrogenous base attaches to its pentose sugar through an N-glycosidic linkage, forming the nucleoside; the sugar in RNA is ribose, while in DNA it is deoxyribose (ribose with the oxygen at the 2' carbon position removed). Two nucleotides join together to form a dinucleotide through a 3'-5' phosphodiester linkage, created by a condensation reaction between the phosphate group of one nucleotide and the sugar of the neighb …