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5. Pyruvate dehydrogenase and the citric acid cycle 5.5 Regulation of the citric acid cycle ATP and NADH inhibit isocitrate dehydrogenase NADH inhibits ?-ketoglutarate dehydrogenase High levels of NADH will lower the oxaloacetate concentration, which limits citrate synthase activity is not only utilized for complete…

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5. Pyruvate dehydrogenase and the citric acid cycle 5.6 Reactions that divert and replenish TCA cycle intermediates Several metabolites in the citric acid cycle are also substrates in biosynthetic pathways, for example those for heme or various amino acids, and through these pathways are drained…

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5. Pyruvate dehydrogenase and the citric acid cycle 5.4 The citric acid cycle The overall reaction of the TCA cycle: does it add up? The citrate synthase reaction Reactions in the TCA: from citrate to oxaloacetate ?-Ketoglutarate dehydrogenase resembles PDH Almost all carbon that accrues…

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4. Catabolism of sugars other than glucose 4.4 Sorbitol is an intermediate of the polyol pathway Sorbitol is not strictly a sugar, since it has no keto or aldehyde group. It is normally a minor component of dietary carbohydrates, but it is also prepared semisynthetically and…

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4. Catabolism of sugars other than glucose 4.1 Dietary sugars other than glucose Trivial name Composition Source lactose (milk sugar) disaccharide of glucose and galactose milk sucrose disaccharide of glucose and fructose sugar cane, sugar beet, other fruits fructose monosaccharide various fruits sorbitol sugar alcohol fruits; semisynthetic…

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4. Catabolism of sugars other than glucose 4.3 Lactose and galactose The Leloir pathway for galactose utilization Mechanism of UDP-galactose epimerase Lactose intolerance Galactosemia Lactose, a disaccharide of glucose and galactose, is the major carbohydrate contained in milk. Like maltose and sucrose, it is…

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2. Refresher 2.2 How enzymes work: Active sites and catalytic mechanisms The “catalytic triad” in the active site of chymotrypsin The catalytic mechanism of chymotrypsin Many enzymes require coenzymes IUBMB classification of enzymes As with all proteins, the activity of enzymes depends on the precise…

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5. Pyruvate dehydrogenase and the citric acid cycle 5.2 Structure and function of pyruvate dehydrogenase The PDH reaction occurs in three successive steps that are catalyzed by three different subunits The structural organization of the PDH complex A lipoamide tether guides the substrate from one active…

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