Important molecules: ADP – Adenosine diphosphate (ADP) (Adenosine pyrophosphate (APP)) is an important organic compound in metabolism and is essential to the flow of energy in living cells. A molecule of ADP consists of three important structural components: a sugar backbone attached to a molecule of adenine and two phosphate groups bonded to the 5 carbon atom of ribose. ATP – A multifunctional nucleotide that is most important as a "molecular currency" of intracellular energy transfer.