The glycolytic pathway converts glucose to pyruvate and produces two molecules of ATP per glucose—only a small fraction of the potential energy available from glucose. Under anaerobic conditions, pyruvate is reduced to lactate in animals and to ethanol in yeast, and much of the potential energy of the glucose molecule remains untapped. In the presence of oxygen, however, a much more interesting and thermodynamically complete story unfolds. Under aerobic conditions, NADH is oxidized in the electron transport chain, rather than becoming oxidized through reduction of pyruvate to lactate or acetaldehyde to ethanol, for example. Further, pyruvate is converted to acetyl-coenzyme A and oxidized to CO2 in the tricarboxylic acid (TCA) cycle (also called the citric acid
Thus times do shift, each thing his turn does hold;
New things succeed, as former things grow old.
Robert Herrick (Hesperides , "Ceremonies for Christmas Eve")
20.1 • Hans Krebs and the Discovery of the
20.3 • The Bridging Step: Oxidative
Decarboxylation of Pyruvate
20.4 • Entry into the Cycle: The Citrate
20.5 • The Isomerization of Citrate by
20.6 • Isocitrate Dehydrogenase—The First
Oxidation in the Cycle
20.7 • a-Ketoglutarate Dehydrogenase—A
20.8 • Succinyl-CoA Synthetase—A Substrate
20.9 • Succinate Dehydrogenase—An
Oxidation Involving FAD
20.10 • Fumarase Catalyzes Trans-Hydration of
20.11 • Malate Dehydrogenase—Completing the Cycle
20.13 • The TCA Cycle Provides Intermediates for Biosynthetic Pathways
20.14 • The Anaplerotic, or "Filling Up,"
20.15 • Regulation of the TCA Cycle
20.16 • The Glyoxylate Cycle of Plants and
Was this article helpful?