| ENERGY PRODUCTION IN THE TCA CYCLE
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| Four oxidative steps provide free energy for ATP synthesis
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| A common end-product of carbohydrate, fatty acid and amino acid metabolism, acetyl-CoA is oxidized in the TCA cycle to produce reduced coenzymes by four redox reactions per turn of the cycle. Three produce reduced nicotinamide adenine dinucleotide (NADH) and another produces reduced flavin adenine dinucleotide (FADH2). These reduced nucleotides provide energy for ATP synthesis by the electron transport system (Chapter 8). One high-energy phosphate, guanosine triphosphate (GTP), is also produced in the cycle by substrate-level phosphorylation. Nearly all metabolic carbon dioxide is produced by decarboxylation reactions catalyzed by pyruvate dehydrogenase and TCA cycle enzymes in the mitochondrion.
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