citric acid cycle

2742 words 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 energy released in the breakage of the bond is used to drive the synthesis of a phosphoanhydride bond in either GTP or ATP. The enzyme that catalyzes the reaction is succinyl-CoA synthetase. In tissues that require large amount of cellular respirations, ADP predominates whereas anabolic reactions require GDP/GTP (Tymoczko, p. 334).
The methylene group (CH2) is converted into a carbonyl group (C=O) in three steps: an oxidation, hydration, and a second oxidation reaction (Tymoczko, p. 335). The energy produced and extracted in the forms of FADH2 and NADH.
6. Oxidation of succinate to fumarate. Succinate formed from succinyl-CoA is oxidized to fumarate by flavoprotein succinate dehydrogenase. FAD is the hydrogen acceptor in the reaction. Succinate dehydrogenase is directly associated with the electron-transport chain transferring two electrons directly from FADH2 to coenzyme CoQ; CoQ passes electrons to the oxygen acceptor (Tymoczko, p. 334). Succinate is oxidized to fumarate; starting the next step of hydration of fumarate to form L-malate.
7. Hydration of fumarate to malate. The hydration of fumarate to L-malate is catalyzed by fumarase. Malate is oxidized to form oxaloacetate and NAD+ is the hydrogen acceptor (Tymoczko, p. 335).
8. Oxidation of Malate to oxaloacetate. This is the last reaction of the citric acid cycle. NAD-linked L-malate dehydrogenase is the oxidation of L-malate to oxaloacetate.


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