In metabolism, complex molecules are broken down into simpler products, including amino acids, glucose, and fatty acids. These simpler molecules can then be broken down into the Acetyl CoA intermediate (Voet, D., Voet, J., Pratt, C. 2006. p. 397). Acetyl CoA then enters the citric acid cycle (TCA cycle) and is oxidized to carbon dioxide, CO2. During the TCA cycle, NAD+ and FADH are reduced to produce high transfer potential electrons, NADH and FADH2. These NADH and FADH2 molecules are oxidized during oxidative phosphorylation and the electron transport chain and generate water, H2O and ATP (Voet et al. 2006. p. 397). Intermediates formed from the citric acid cycle are important precursors and building blocks for the production of important materials in an organism. These intermediates are removed from the TCA cycle in cataplerotic reactions to synthesize important products such as glucose, fatty acids, and amino acids. For example, gluconeogenesis, the synthesis of glucose, requires oxaloacetate that has been converted to malate, while fatty acid biosynthesis uses acetyl CoA and amino acid biosynthesis uses oxaloacetate and α -ketoglutarate (Tymoczko, JL, Berg, JM and Stryer, L. 2013. p. 339). During the TCA cycle, pyruvate is oxidized to acetyl CoA, which undergoes a condensation reaction catalyzed by citrate synthase to form citrate. Citrate can then be isomerized to form isocitrate, which undergoes oxidative carboxylation catalyzed by isocitrate dehydrogenase, to form α-ketoglutarate. Succinyl CoA is then formed from the decarboxylation/oxidation of α-ketoglutarate, which is catalyzed by α-ketoglutarate dehydrogenase. Succinyl CoA can be used to form products including chlorophyll, heme, and prophyr...... middle of paper ......409). In order to synthesize a sugar from the hexose monophosphate pool, two molecules of dihydroxyacetone phosphate (DHAP) are also needed. Six cycles of the Calvin cycle must take place to synthesize a hexose sugar. For each CO2 molecule, three ATP and two NADPH are used to convert CO2 to hexose. A total of 12 ATPs are used to phosphorylate 12 molecules of 3-phosphoglycerate to 1,3-bisphosphoglycerate (1,3-BPG). 12 NADH are then used to reduce the 12 molecules of 1,3-bisphosphoglycerate to glyceraldehyde 3-phosphate (Tymoczko et al. 2013. p. 410-412). Works Cited Tymoczko, JL, Berg, JM and Stryer, L. (2013). Biochemistry: A Short Course, 2nd Edition. New York, NY: WH Freeman and Co. Voet, D., Voet, J., and Pratt, C. (2006). Fundamentals of Biochemistry: Life at the Molecular Level, 2nd Edition. Hoboken, New Jersey: John Wiley & Sons, Inc...