Aerobic Respiration: Summary

Having studied each stage, we can now follow a glucose molecule all the way through aerobic respiration.Carbon: the six carbon atoms of glucose end up in carbon dioxide. None are lost in glycolysis; two leave as CO₂ in the link reaction and four in the Krebs cycle (two turns). This accounts for the 6CO₂ in the overall equation.Hydrogen: hydrogen atoms are removed by dehydrogenases in glycolysis, the link reaction and the Krebs cycle, and carried by reduced NAD and reduced FAD to the electron transport chain, where they are split into protons and electrons.Oxygen: oxygen is used only at the very end, as the final electron acceptor, combining with electrons and protons to form the 6H₂O of the equation.Energy: a small amount of ATP is made by substrate-level phosphorylation (glycolysis and Krebs cycle), but most is made by oxidative phosphorylation, through the electron transport chain and chemiosmosis.The stages depend on each other. If oxygen runs out, the electron transport chain stops, NAD is not regenerated, and the Krebs cycle and link reaction stop. Only glycolysis can continue, provided pyruvate is converted to lactate or ethanol.Summary:
• Glycolysis (cytoplasm): glucose → 2 pyruvate; net 2 ATP, 2 reduced NAD
• Link reaction (matrix): 2 acetyl CoA, 2 CO₂, 2 reduced NAD
• Krebs cycle (matrix): 4 CO₂, 2 ATP, 6 reduced NAD, 2 reduced FAD
• Oxidative phosphorylation (cristae): most of the ATP, and water