Nucleoside diphosphate

A nucleoside diphosphate is a molecule formed by a purine or a pyrimidine binding to a carbohydrate (forming a nucleoside) bound to two phosphate groups that are connected to each other by a pyrophosphate bond. The main nucleoside diphosphates are ADP and GDP (purine nucleotides) and CDP and UDP (pyrimidine nucleotides).