The Citric Acid Cycle Acetyl Coenzyme A??-? A small molecule that carries acetyl functional groups in cells. Composed of an acetyl group attached to a coenzyme A molecule. The starting product of the citric acid cycle. Acontinase??-? The citric acid cycle enzyme responsible for catalyzing the reaction that converts citric acid to isocitrate with the release of water. Adenisine Triphosphate (ATP)??-? The molecule from which cells derive energy. Comprised of an adenisine molecule bonded to three phosphates, each phosphate bond contains energy, especially the third bond. By breaking that one bond and reducing ATP to adenisine?diphosphate (ADP), the cell can get the energy to carry out its various processes.