Metabolism gets completed in three stages, i.e., glycolysis for glucose, citric acid cycle, and electron transport chain. Glucose gets broken down into energy in the first stage (glycolysis for glucose). The second stage, also known as the Krebs and tricarboxylic acid cycle, leads to the production of fatty acids, porphyrins, amino acids, and other important compounds. The third stage, i.e., the electron transport chain, results in a series of reactions that leads to ATP creation.