Citric acid cycle: Difference between revisions
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The Citric acid cycle, also known as the Krebs cycle or the Tricarboxylic acid cycle, takes place in the mitochondrial matrix. It can be divided into 3 steps: | The Citric acid cycle, also known as the Krebs cycle or the Tricarboxylic acid cycle, takes place in the [[Mitochondrial matrix|mitochondrial matrix]]. It can be divided into 3 steps: | ||
#The [[Acetyl CoA|acetyl CoA]] combines with a 4C compound, [[Oxaloacetate|oxaloacetate]], to form a 6C compound, [[Citrate|citrate]]. | |||
#The citrate is [[Decarboxylated|decarboxylated]] ([[Carbon dioxide|carbon dioxide]] removed) and [[Dehydrogenated|dehydrogenated]] (oxidised by the removal of [[Hydrogen|hydrogen]]) in a series of steps. At 2 steps, carbon dioxide is removed and given off as a waste gas. At 4 places, pairs of [[Hydrogen|hydrogen]] [[Atoms|atoms]] are removed and accepted by [[NAD|NAD]] and [[FAD|FAD]] which get reduced to [[NADH2|NADH2]] and [[NADH2|FADH2]] respectively. | |||
#[[Oxaloacetate|Oxaloacetate]] is regenerated to combine with the second [[Acetyl CoA|acetyl CoA]]. | |||
Thus, for each turn of the cycle, 2 carbon dioxide molecules are formed. One reduced FAD and 3 reduced NAD are also formed and 1 ATP molecule is generated. | |||
| For 1 mole of [[Glucose|glucose]], that is both moles of acetyl CoA, the Citric acid cycle yields: | ||
*8 pairs of [[hydrogen|hydrogen]] [[atoms|atoms]], | |||
*2 [[molecules|molecules]] of [[ATP|ATP]] and | |||
*4 molecules of [[carbon|carbon]] dioxide. | |||
The pairs of hydrogen atoms will be channelled on the inner membrane of the [[Mitochondria|mitochondria]] to be used in [[Oxidative phosphorylation|oxidative phosphorylation]] to provide energy to make ATP<ref>Clackamas Community College (2003) Citric Acid Cycle. Available at: dl.clackmas..edu/ch106-06/citric.htm (01/12/2011)</ref><ref>Essential Biochemistry. Citric Acid Cycle. Available at: www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html (29/11/2011)</ref><ref>Jeremy M.Berg, John L.tymoczko, Lubert Stryer (2007) Biochemistry, 7th Edition, England, FREEMAN. (30/11/2011)</ref>. | |||
The Citric acid cycle is regulated by several enzymes, in contrast to the preceding process of [[glycolysis|glycolysis]] which is primarily regulated by [[PFK-1|PFK-1]]. The most important enzymes are those that catalyze reactions with highly negative delta G<sup>0</sup>. The 3 [[enzymes|enzymes]] responsible are; [[citrate synthase|citrate synthase]], which produces [[citrate|citrate]] by synthesis of [[oxaloacetate|oxaloacetate]] and acetyl CoA. [[Isocitrate dehydrogenase|Isocitrate dehydrogenase]], which is the [[oxidative decarboxylation|oxidative decarboxylation]] of [[isocitrate|isocitrate]]. Finally, [[alpha-ketoglutarate dehydrogenase complex|alpha-ketoglutarate dehydrogenase complex]], which [[oxidatively carboxylates|oxidatively carboxylates]] [[alpha-ketoglutarate|alpha-ketoglutarate]] to [[succinyl CoA|succinyl CoA]]<ref>Ferrier D. Lippincott's illustrated reviews biochemistry, 6th Edition. Lippincott Williams and Wilkins, Baltimore.</ref>.<sup></sup> | |||
=== Reference === | |||
<references /> | |||
Latest revision as of 09:31, 8 December 2018
The Citric acid cycle, also known as the Krebs cycle or the Tricarboxylic acid cycle, takes place in the mitochondrial matrix. It can be divided into 3 steps:
- The acetyl CoA combines with a 4C compound, oxaloacetate, to form a 6C compound, citrate.
- The citrate is decarboxylated (carbon dioxide removed) and dehydrogenated (oxidised by the removal of hydrogen) in a series of steps. At 2 steps, carbon dioxide is removed and given off as a waste gas. At 4 places, pairs of hydrogen atoms are removed and accepted by NAD and FAD which get reduced to NADH2 and FADH2 respectively.
- Oxaloacetate is regenerated to combine with the second acetyl CoA.
Thus, for each turn of the cycle, 2 carbon dioxide molecules are formed. One reduced FAD and 3 reduced NAD are also formed and 1 ATP molecule is generated.
For 1 mole of glucose, that is both moles of acetyl CoA, the Citric acid cycle yields:
The pairs of hydrogen atoms will be channelled on the inner membrane of the mitochondria to be used in oxidative phosphorylation to provide energy to make ATP[1][2][3].
The Citric acid cycle is regulated by several enzymes, in contrast to the preceding process of glycolysis which is primarily regulated by PFK-1. The most important enzymes are those that catalyze reactions with highly negative delta G0. The 3 enzymes responsible are; citrate synthase, which produces citrate by synthesis of oxaloacetate and acetyl CoA. Isocitrate dehydrogenase, which is the oxidative decarboxylation of isocitrate. Finally, alpha-ketoglutarate dehydrogenase complex, which oxidatively carboxylates alpha-ketoglutarate to succinyl CoA[4].
Reference
- ↑ Clackamas Community College (2003) Citric Acid Cycle. Available at: dl.clackmas..edu/ch106-06/citric.htm (01/12/2011)
- ↑ Essential Biochemistry. Citric Acid Cycle. Available at: www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html (29/11/2011)
- ↑ Jeremy M.Berg, John L.tymoczko, Lubert Stryer (2007) Biochemistry, 7th Edition, England, FREEMAN. (30/11/2011)
- ↑ Ferrier D. Lippincott's illustrated reviews biochemistry, 6th Edition. Lippincott Williams and Wilkins, Baltimore.