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The aerobic respiration is divided into four steps:

  1. Glycolysis: Glycolysis takes place in the cytoplasm; here the glucose is broken down into 2 molecules of pyruvic acid. It results in the production of 2 ATP molecules.
  2. Transition Reaction: This step takes place in the mitochondria where the pyruvic acid is transformed into acetyl CoA. This acetyl CoA enters the Krebs cycle.
  3. Krebs cycle: Krebs cycle or citric acid cycle takes place in the mitochondrial matrix in the presence of oxygen. The oxalo acetic acid regenerated at the end of the Krebs cycle, which again combines with acetyl CoA to form the citric acid in the next turn of the cycle. The Krebs cycle results in the production of 2 GTP, 6NADH+H+ and FADH2 molecules.
  4. The electron transport chain and chemiosmosis: It occurs in the cristae of the mitochondria. The H+ ions which are released in the matrix are transferred to the electron transport chain by the two hydrogen acceptor molecules. The electron transport chain consists of chain of coenzyme and cytochromes. Electron transport chain produces a gain of 32 ATP molecules. The ATP production occurs by the movement of H+ across the concentration gradient with the aid of the enzyme ATP synthase. Thus a net gain of 36 ATP molecules is produced during aerobic respiration of one molecule of glucose in the prokaryotes. Where as in the eukaryotes 2ATP molecules are used up in transporting the NADH2 molecules to the mitochondria so there is net gain of only 36 ATP molecules.