chambers33 - CITRIC ACID CYCLE CITRIC -Pyruvate...

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CITRIC ACID CYCLE CITRIC ACID CYCLE -Pyruvate Dehydrogenase -Pyruvate Dehydrogenase Reading: Harper’s Biochemistry Chapter 18 Lehninger Principles of Biochemistry 3rd Ed. pp. 567-583
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OBJECTIVES OBJECTIVES To understand how the pyruvate dehydrogenase complex acts as a mediator of flow of carbon compounds between the glycolytic pathway and the citric acid cycle. To understand the central role of the citric acid cycle in mitochondrial energy metabolism. The structures of the intermediates in the cycle. The names of the enzymes that catalyze each step. The cofactors and products involved in each step.
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The citric acid cycle (Krebs cycle, tricarboxylic acid cycle) is a series of reactions in mitochondria that bring about the catabolism of acetyl residues. The acetyl groups are fed into the citric acid cycle, which enzymatically oxidizes them to CO 2 . The energy released by oxidation is conserved in the reduced electron carriers NADH and FADH 2 . The reduced coenzymes are then oxidized themselves, giving up protons and electrons. The electrons are transferred, eventually, to O 2 , via a chain of electron-carrying molecules known as the respiratory chain. In the course of electron transfer, the large amount of energy released is conserved in the form of ATP
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Catabolism of Catabolism of proteins, fats, proteins, fats, and and carbohydrates carbohydrates in the three in the three steps of steps of cellular cellular respiration respiration
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Biomedical Importance Biomedical Importance The citric acid cycle acts as a final common pathway for the oxidation of carbohydrate, lipids, and protein, because glucose, fatty acids, and many amino acids can all be metabolized to acetyl-CoA or intermediates in the cycle. The citric acid cycle also plays a major role in gluconeogenesis, transamination, deamination, and lipogenesis. The liver is the only tissue where all of these occur to a significant extent. When large numbers of liver cells are damaged or destroyed, in acute hepatitis or cirrhosis, this can have major repercussions on metabolism. Very few genetic abnormalities exist for enzymes of the citric acid cycle, suggesting such abnormalities are incompatible with normal development and highlighting the vital nature of the process. Pyruvate hydrogenase is a key enzyme needed to convert pyruvate to acetyl-CoA. A variety of disorders in pyruvate metabolism are due to defects in this enzyme.
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Sources of acetyl-CoA in mitochondria
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Pyruvate transport into mitochondria Pyruvate generated in the cytoplasm by glycolysis must be transported across the inner mitochondrial membrane via a pyruvate/H + symport. This transport uses some of the energy stored in
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This note was uploaded on 12/16/2011 for the course BIOLOGY 101 taught by Professor Mr.wallace during the Fall '11 term at Montgomery College.

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chambers33 - CITRIC ACID CYCLE CITRIC -Pyruvate...

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