Cellular respiration is a series of chemical reactions that break down glucose to produce ATP, which may be used as energy to power many reactions throughout the body. There are three main steps of cellular respiration: glycolysis, the citric acid cycle, and oxidative phosphorylation. Glycolysis takes place in the cytosol, the citric acid cycle occurs in the mitochondrial matrix, and oxidative phosphorylation occurs on the inner mitochondrial membrane. The starting reactants of cellular respiration include glucose, ATP, and NAD+; and the final products include ATP and H2O. The rate-determining enzymes for cellular respiration include phosphofructokinase-1, pyruvate dehydrogenase, and isocitrate dehydrogenase. Diseases that affect cellular respiration typically disrupt one or more enzymes involved in the process, such as pyruvate kinase or succinyl-CoA-synthase.