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SURVEY OF BIOCHEMISTRY Citric Acid Cycle. Formation of Acetyl CoA. Acetyl CoA is a metabolic intermediate that can be produced from amino acids, glucose (via pyruvate), and fatty acids.
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Formation of Acetyl CoA Acetyl CoA is a metabolic intermediate that can be produced from amino acids, glucose (via pyruvate), and fatty acids This rxn is the first of 5 dehydrogenase reactions.Here oxidation of pyruvate to acetyl CoA (and reduction of NAD+ to NADH) leads to the production of CO2.
Formation of Citrate Citrate is a tricarboxylic acid. The citric acid cycle is sometimes referred to as the Tricarboxylic Acid (TCA) Cycle.
Formation of Isocitrate Notice that aconitase catalyzes this reaction in both directions!
Formation of Alpha-Ketoglutarate Notice that the carbon that is cleaved off of isocitrate did not come from the carbons in acetyl CoA! This rxn is the second of 5 dehydrogenase reactions.
Formation of Succinyl-CoA This rxn is the third of 5 dehydrogenase reactions.Here a 5-C molecule is converted into a 4-C precursor.
Formation of Succinate GTP is equivalent to an ATP in terms of the energy yield from hydrolysis.
Formation of Fumarate This rxn is the fourth of 5 dehydrogenase reactions.FAD is the redox cofactor used by succinate dehydrogenase.
Formation of Oxaloacetate This rxn is the fifth of 5 dehydrogenase reactions.Oxaloacetate has now been regenerated so that it can react with a new molecule of acetyl CoA to repeat the cycle.
ATP Accounting Glycolysis Glycolysis TCA Cycle TCA Cycle ATP 2 0 0 GTP 0 0 2 NADH 2 2 6 FADH2 0 0 2 Each GTP is equivalent to 1 ATP Each NADH is equivalent to 2.5 ATP’s Each FADH2 is equivalent to 1.5 ATP’s
ATP Accounting TOTAL ATP Equivalents ATP 2 2 GTP 2 2 NADH 10 25 FADH2 2 3 One molecule of glucose gets metabolized into~32 ATP’s Each GTP is equivalent to 1 ATP Each NADH is equivalent to 2.5 ATP’s Each FADH2 is equivalent to 1.5 ATP’s
Summary • Read Chapter 17.1-17.4 • Learn each step of the TCA Cycle • Substrates • Products • Reactants • Cofactors • Next Monday • Mechanisms in the TCA Cycle • Control of the TCA Cycle