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6.3.1.2. Energy production under anaerobic and aerobic condition
a. Aerobic condition Under aerobic condition, pyruvate is taken up into mitochondria, and after conversion to acety-CoA is oxidized to CO2 by the citric acid cycle. The reducing equivalents from the NADH+H+ formed in glycolysis are taken up into mitochondria for oxidation. Two triosephosphates are produced from each molecule of hexose metabolized. Dihydroxyacetone phosphate can be isomerized by isomerase to glyceraldehyde 3 phosphate which is then converted to 1, 3 diphosphoglyceric acid by glyceraldehyde 3 phosphate dehydrogenase system requiring NAD+ and inorganic phosphate.
ATP Production: ATP Conversion of 1, 3 diphosphoglycerateto 3 phosphoglycerate : 2 Conversion of phosphoenol pyruvate to enol pyruvate : 2 Action of glyceraldehyde 3 phosphatedehydrogenase and ETC (2x3) : 6 -------- Total :10 -------- ATP molecules used up in the initial reactions : 2 --------- Net ATP production : 8 --------- b. Anaerobic condition If anaerobic conditions prevail, the reoxidation of NADH by transfer of reducing equivalents through the respiratory chain to oxygen is prevented. Then, pyruvate is reduced by the NADH+H+ to lactate, the reaction being catalyzed by lactate dehydrogenase. The reoxidation of NADH via lactate formation allows glycolysis to proceed in the absence of oxygen by regenerating sufficient NAD+ for another cycle of the reaction catalyzed by glyceraldehyde-3 phosphate dehydrogenase.
Pyruvate + NADH + H+ ↔ NAD+ + Lactate During fermentation, pyruvate is reduced by NADH to ethyl alcohol being catalysed by alcohol dehydrogenase. Alcohol dehydrogenase Pyruvate + NADH + H+ ↔ NAD+ + Ethyl alcohol ATP production: ATP
Conversion of two triose phosphates to lactic acid (or ethanol): 4. ATP molecules used up in the initial reactions : 2 ---------- Net ATP production : 2 ----------
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