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pdh, citric cycle

pdh, citric cycle - Pyruvate Dehydrogenase Complex Enzyme...

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Pyruvate Dehydrogenase Complex, Enzyme Cofactors, and the Citrate Cycle Bioc 460 Spring 2010 Lectures 26 and 27 Dr. Lisa Rezende What happens to pyruvate under aerobic conditions? Why is the citrate cycle the “hub” of metabolism? What are coenzymes and why do we need them? Image credit: Morguefile
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Learning Objectives Lectures 25 and 26 Describe the three separate reactions catalyzed by pyruvate dehydrogenase. List the co-factors in the catalytic mechanisms of pyruvate dehydrogenase and discuss their relationship to vitamin deficiencies. Write the overall balanced chemical equation for citrate cycle listing the starting substrates, products, and the electron carriers. Describe the steps in citrate cycle that are involved in energy transfer. Compare and contrast the energetics of thioester hydrolysis in acetyl-CoA with hydrolysis of phosphoanhydride bond in ATP. List the key regulators of the citrate cycle and explain how they fit into a larger metabolic context. Describe the role of pyruvate carboxylase in regulating flux through the citrate cycle. Discuss the physiological function of glyoxylate pathway. Reading: Review Chapter 15, Read Chapter 17 Problems: End of chapter (499-501): 5, 6, 9, 15 (focus on part a and d)
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Citrate cycle : also know as the Krebs cycle, tricarboxylic acid cycle (TCA), and the citric acid cycle (CAC). Note that the citrate cycle plays key roles in the oxidation of Glucose and fatty acids, as well as the synthesis of amino acids, carbohydrates, and lipids. Figure courtesy of Dr. R.L. Miesfeld
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In eukaryotes, metabolic pathways are segregated into different parts of the cell Glycolysis occurs in the cytoplasm Decarboxylation of pyruvate and the citrate cycle occur in the mitochondrial matrix What are the advantages to compartmentalizing metabolic reactions?
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The reactions of the pyruvate dehydrogenase complex link glycolysis to the citrate cycle. Pyruvate + CoA + NAD+ -> acetyl-CoA + CO2 + NADH + H+ Note the reaction transfers two electrons to NADH Why must this occur under aerobic conditions?
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Coenzyme A In its role as an “activated carrier” molecule it carries acetate molecules (2 carbons) in a variety of metabolic pathways including fatty acid oxidation and synthesis, and glucose Oxidation Acetyl CoA is composed of an acetate molecule covalently attached to CoA through an activated thioester bond
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Pyruvate dehydrogenase is the link between glycolysis and oxidation of pyruvate in citric acid cycle .
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