adenosine diphosphate (ADP) a nucleotide, adenosine 5′-pyrophosphate, produced by the hydrolysis of adenosine triphosphate (ATP). It is then converted back to ATP by the metabolic processes oxidative phosphorylation, glycolysis, and the tricarboxylic acid cycle. compound derived from nucleic acid, composed of adenine and a sugar, d-ribose. Adenosine is the major molecular component of the nucleotides adenosine diphosphate, adenosine monophosphate, and adenosine triphosphate and of the nucleic acids DNA and RNA. Also called adenine-d-ribose. See also adenosine phosphate.