An Overview of Metabolism and Biochemical Energy Stage 3 Citric acid cycle Acetyl groups are oxidized inside cellular mitochondria to yield CO2 This stage releases a large amount of energy Stage 4 The electron transport chain Energy made in the citric acid cycle used during the fourth stage,the electron-transport chain,to accomplish the endergonic phosphorylation of ADP with hydrogen phosphate ion(HOPO32-,abbreviated Pi)to give ATPStage 3 Citric acid cycle ▪ Acetyl groups are oxidized inside cellular mitochondria to yield CO2 ▪ This stage releases a large amount of energy Stage 4 The electron transport chain ▪ Energy made in the citric acid cycle used during the fourth stage, the electron-transport chain, to accomplish the endergonic phosphorylation of ADP with hydrogen phosphate ion (HOPO3 2- , abbreviated Pi) to give ATP An Overview of Metabolism and Biochemical Energy