Biological oxidation involves the loss of electrons and/or hydrogen atoms from a substrate. This process is carried out by enzymes and can involve the loss of electrons, hydrogen atoms, or addition of oxygen atoms. Energy released from exergonic reactions is transferred through common intermediates to drive endergonic reactions. Adenosine triphosphate (ATP) is often used as an energy carrier in coupled reactions, transferring phosphate groups from energy-rich intermediates to adenosine diphosphate (ADP) to form ATP. During metabolism, electrons from metabolic intermediates are transferred to electron carriers like NADH and FADH2 in the electron transport chain located in the inner mitochondrial membrane. As electrons are passed

1. BIOLOGICAL OXIDATION

26. Electron Carriers NAD + or FAD There are 2 sites of entry for electrons into the electron transport chain: Both are coenzymes for dehydrogenase enzymes The transfer of electrons is not directly to oxygen but through coenzymes

34. Reduction Potentials Number of electrons transferred in the redox reaction Faraday’s constant (96485 J/volt/mole) Crucial equation:   G o ' = -n F  E o ' The relative tendency to accept e - s and become reduced.  = E o '(acceptor) - E o '(donor) E 0 ’=standard reduction potential. If  E o ' is positive, an electron transfer reaction is spontaneous (  G o ' <0)

35. OXIDATIVE PHOSPHORYLATION

44. CYTOPLASM OUTER MEMBRANE MATRIX INNER MEMBRANE Figure 3. The malate-aspartate shuttle. OAA Malate (1) e - NAD + e - Glu 0 (6) Glu 0 Asp -1 (4) KG KG Malate (2) e - e - OAA NADH NAD + (3) e - Complex I e - NAD + Glucose Pyruvate GLYCOLYSIS NADH Asp -1 (5)

45. CYTOPLASM INNER MEMBRANE MATRIX FAD Glycerol-3-phosphate dehydrogenase (2) DHAP OUTER MEMBRANE Figure 4. Glycerol phosphate shuttle. Cytoplasmic glycerol 3-phosphate dehydrogenase (1) oxidizes NADH. Glycerol 3-phosphate dehydrogenase in the inner membrane (2) reduces FAD to FADH 2 . G3P Dihydroxyacetone phosphate (DHAP) NAD + 3-phosphate Glycerol e  (1) FADH 2 e  CoQ e  O 2 e  NADH Glucose Pyruvate GLYCOLYSIS NAD +