Justify why movement of 2 electrons in complex IV influx 2 H into the inter membrane space instead of 4 II (like complex I and complex III through which 2 electrons movement influx 4 II).
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Most of the free energy released during the oxidation of glucose to CO2 is retained in the reduced coenzymes NADH and FADH2 generated during glycolysis and the citric acid cycle. During respiration, electrons are released from NADH and FADH2 and eventually are transferred to O2, forming H2O according to the following overall reactions:
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The ΔG°′ values for these strongly exergonic reactions are −52.6 kcal/mol (NADH) and −43.4 kcal/mol (FADH2). Recall that the conversion of one glucose molecule to CO2 via the glycolytic pathway and citric acid cycle yields 10 NADH and 2 FADH2 molecules (see Table 16-1). Oxidation of these reduced coenzymes has a total ΔG°′ of −613 kcal/mol [10(−52.6) + 2(−43.4)]. Thus, of the potential free energy present in the chemical bonds of glucose (−680 kcal/mol), about 90 percent is conserved in the reduced coenzymes.
The free energy released during oxidation of a single NADH or FADH2 molecule by O2 is sufficient to drive the synthesis of several molecules of ATP from ADP and Pi, a reaction with a ΔG°′ of +7.3 kcal/mol. The mitochondrion maximizes the production of ATP by transferring electrons from NADH and FADH2 through a series of electron carriers all but one of which are integral components of the inner membrane. This step-by-step transfer of electrons via the electron transport chain (also known as the respiratory chain) allows the free energy in NADH and FADH2 to be released in small increments. At several sites during electron transport from NADH to O2, protons from the mitochondrial matrix are transported uphill across the inner mitochondrial membrane and a proton concentration gradient forms across it (Figure 16-17). Because the outer membrane is freely permeable to protons, the pH of the mitochondrial matrix is higher (i.e., the proton concentration is lower) than that of the cytosol and intermembrane space. An electric potential across the inner membrane also results from the uphill pumping of positively charged protons outward from the matrix, which becomes negative with respect to the intermembrane space. Thus free energy released during the oxidation of NADH or FADH2 is stored both as an electric potential and a proton concentration gradient — collectively, the proton-motive force — across the inner membrane. The movement of protons back across the inner membrane, driven by this force, is coupled to the synthesis of ATP from ADP and Pi by the