citric acid cycle Essay

2742 Words Dec 28th, 2013 11 Pages
Describe the role of the citric acid cycle as a central metabolic mechanism. Explain what happens to the cells’ abilities to oxidize acetyl CoA when intermediates of the cycle are drained off for amino acid biosynthesis.
Glucose is a source of energy that is metabolized into glycolysis to pyruvate yielding ATP. To become more efficient, pyruvate must be oxidized into carbon dioxide and water. This combustion of carbon dioxide and water to generate ATP is called cellular respiration (Tymoczko, Berg & Stryer, 2013, p. 315). In eukaryotic cells, this aerobic process is used because of the efficiency.
Cellular respiration is divided into parts: carbon fuels are completely oxidized with a concomitant generation of high transfer
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The enzyme aconitase catalyzes the reversible transformation of citrate to isocitrate through formation of tricarboxylic acid cis-aconitate. Citrate is isomerized into isocitrate to enable the six carbon unit to undergo oxidative decarboxylation allowing a dehydration and hydration step of citrate (Tymoczko, p. 332). Aconitase can promote the reversible addition of H2O to double bond of enzyme-bound cis-anonitate in two ways: one leading to citrate and the other to isocitrate.
3. Oxidation of isocitrate to a-ketoglutarate and CO2. Isocitrate dehydrogenase catalyzes oxidative decarboxylation of isocitrate to form a-ketoglutarate. The two forms of isocitrate dehydrogenase require NAD+ as electron acceptor and NADP+. This intermediate reaction is oxalosuccinate (unstable alpha-ketoacid). The enzyme loses CO2 to form alpha-ketoglutarate which generates the first high-transfer potential electron carrier in the cycle NADH through oxidation (Tymoczko, p. 332).
4. Oxidation of a-ketoglutarate to succinyl-CoA and CO2. Oxidative decarboxylation of a-ketoglutarate is converted to succinyl-CoA and CO2 by the a-ketoglutarate dehydrogenase complex. During this portion of citric acid cycle, the two carbon atoms have entered the cycle and two carbon atoms have been oxidized to CO2. The electrons from oxidations are captured in two molecules of NADH (Tymoczko, p. 333).
5. Conversion of Succinyl-CoA to succinate. Succinyl-CoA has a thioester

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