Krebs Cycle: The Citric Acid Cycle (TCA) PDF

Krebs Cycle The Citric Acid Cycle (TCA)  THE CITRIC ACID CYCLE PROVIDES SUBSTRATES FOR THE RESPIRATORY CHAIN The citric acid cycle (the Krebs or tricarboxylic acid cycle) is a sequence of reactions in mitochondria that oxidizes the acetyl moiety of acetyl-CoA to CO2 and...

Krebs Cycle The Citric Acid Cycle (TCA)  THE CITRIC ACID CYCLE PROVIDES SUBSTRATES FOR THE RESPIRATORY CHAIN The citric acid cycle (the Krebs or tricarboxylic acid cycle) is a sequence of reactions in mitochondria that oxidizes the acetyl moiety of acetyl-CoA to CO2 and reduces coenzymes that are reoxidized through the electron transport chain linked to the formation of ATP. The citric acid cycle is the final common pathway for the oxidation of carbohydrate, lipid, and protein because glucose, fatty acids, and most amino acids are metabolized to acetyl-CoA or intermediates of the cycle. It also has a central role in gluconeogenesis, lipogenesis, and interconversion of amino acids. Many of these processes occur in most tissues, but liver is the only tissue in which all occur to a significant extent. Figure 14.2 Structure of ATP and ADP complexed with Mg2+ Textbook of Biochemistry with Clinical Correlations, 7e edited by Thomas M. Devlin © 2011 John Wiley & Sons, Inc. Figure 14.17 General description of oxidation of foodstuffs to provide energy for ATP synthesis within mitochondria. Textbook of Biochemistry with Clinical Correlations, 7e edited by Thomas M. Devlin © 2011 John Wiley & Sons, Inc. Oxidative decarboxylation of pyruvate 6 1. Synthesis of citrate from acetyl CoA and oxaloacetate 2. Isomerization of citrate 3.Oxidation and decarboxylation of isocitrate 4. Oxidative decarboxylation of α-ketoglutarate 5. Cleavage of succinyl CoA 6. Oxidation of succinate 7. Hydration of fumarate 8. Oxidation of malate Energy yield per Acetyl-CoA per turn of cycle 1 acetate unit generates approximately 12 molecules of ATP. In dramatic contrast, only 2 molecules of ATP are generated per molecule of glucose (which generates 2 molecules of acetyl CoA) by anaerobic glycolysis. Molecular oxygen does not participate directly in the citric acid cycle. However, the cycle operates only under aerobic conditions because NAD+ and FAD can be regenerated in the mitochondrion only by the transfer of electrons to molecular oxygen.