1.9

• NADH


  For each mole of NADH oxidized in the ETC, 2.5 moles of ATP are formed
• FADH2


  FADH2, which does not enter the ETC at its start, produces only 1.5 moles of ATP per mole of FADH2 oxidized
• FADH2's entrance point into the chain, complex II, is beyond the first "proton-pumping" site, complex I. Hence fewer ATP molecules are produced from FADH2 than from NADH.
• Summary of the Common Metabolic Pathway

  1. Electron transport chain

  2. Oxidative phosphorylation

  3. Citric acid cycle
• Some of the energy released at each of the protein complexes I, III, and IV is consumed in the movement of H ions across the inner membrane from the matrix into the intermembrane space.
• Movement of ions from a region of lower concentration (the matrix) to one of higher concentration (the intermembrane space) requires the expenditure of energy because it opposes the natural tendency, as exhibited in the process of osmosis (Section 8.9), to equalize concentrations.
• Without oxygen as the final electron acceptor in the ETC, the ETC chain shuts down and ATP production stops. Without ATP to power life's processes (Chapters 24–26), these processes stop.
• Brown fat tissue is specialized for heat production. It contains many more blood vessels and mitochondria than white fat.
• Thermogenin


  A protein in the mitochondria of brown fat cells that functions as an uncoupling agent, "uncoupling" the ATP production associated with the electron transport chain
• The energy of the proton gradient, no longer useful for ATP synthesis, is released as heat.
• Every acetyl CoA entering the citric acid cycle (CAC) produces three NADH, one FADH2, and one GTP (which is equivalent in energy to ATP; Section 23.6). Thus 10 molecules of ATP are produced for each acetyl CoA catabolized.
• The cycling of ATP and ADP in metabolic processes is the principal medium for energy exchange in biochemical processes.
• The conversion ATP -> ADP + Pi powers life processes (the biosynthesis of essential compounds, muscle contraction, nutrient transport, and so on). The conversion Pi + ADP -> ATP replenishes the ATP supply.