The Krebs cycle is also called the tricarboxylic acid (TCA) cycle or citric acid cycle. It is the continuation of aerobic cellular respiration after glycolysis, and it takes place in the mitochondrial matrix. During the Krebs cycle preparation step, pyruvate is transformed to acetyl-CoA. After this, several Krebs cycle reactions couple the oxidation of pyruvate to CO2, reduce the electron carriers NAD+ and FAD , and produce ATP via substrate-level phosphorylation. The reduced electron carriers (NADH and FADH2) are used in the electron transport chain to produce more ATP by oxidative phosphorylation.