Citric Acid Cycle: Difference between revisions

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David Canner, Ann Taylor, Jaime Prilusky, Wayne Decatur, Alexander Berchansky

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 *[[Krebs cycle overview]]
 *[[Krebs cycle reactions]]
-The [[Citric Acid Cycle]] (tricarboxylic acid cycle) is a series of enzyme catalyzed reactions which are critical in cellular respiration. Under oxidative conditions, pyruvate continues to be metabolized through the tricarboxylic acid cycle. In this cycle, Acetyl-CoA, a byproduct of [[glycolysis]], along with various cofactors, are broken down into carbon dioxide, water, and energy in the form of GTP and NADH.
+*[[Major metabolic pathways converging on the citric acid cycle]]
+*[[Citric acid cycle intermediates serve as substrates for biosynthetic processes]]
-'''Step 0 / 10 - Aldol condensation - Citrate synthase'''
+The [[Citric Acid Cycle]] (tricarboxylic acid cycle) is a series of enzyme catalyzed reactions which are critical in cellular respiration. Under oxidative conditions, pyruvate continues to be metabolized through the tricarboxylic acid cycle. In this cycle, Acetyl-CoA, a byproduct of [[glycolysis]], along with various cofactors, are broken down into carbon dioxide, water, and energy in the form of GTP and NADH.
+'''Pyruvate decarboxylation or pyruvate oxidation''', also known as the link reaction (or oxidative decarboxylation of pyruvate), is the conversion of <scene name='39/392339/Cv1/11'>pyruvate</scene> into <scene name='43/430893/Cv/2'>Acetyl-CoA</scene> by the enzyme complex pyruvate dehydrogenase complex (see [[Pyruvate dehydrogenase]]).
+The multienzyme complex together catalyzes five distinct reactions in the conversion of pyruvate to Acetyl-CoA. The overall result is described by the following reaction:
+Pyruvate + CoA + NAD+ ==> Acetyl-CoA + CO2 + NADH
+However, pyruvate dehydrogenase (E1) is responsible for only the first two of the five reactions. The first of these is the decarboxylation of pyruvate and coupling of thiamine pyrophosphate (TPP) to form hydroxyethyl-TPP.
+Pyruvate + TPP ==> Hydroxyethyl-TPP + CO2
+''' Step 0 / 10 - Aldol condensation - Citrate synthase'''
 *[[Citrate Synthase]]
-*[[Krebs cycle step 1]]
+*Step 0 / 10 = [[Krebs cycle step 1]]
 *[[ATP-citrate synthase]]
+C <scene name='43/430893/Cv/3'>oxaloacetate</scene> to a 6C molecule <scene name='43/430893/Cv/4'>citrate</scene>
 '''Step 1 - Dehydration - Aconitase'''
+* [[Aconitase]]
+*1st step of [[Krebs cycle step 2]]
+C Citrate => 6C <scene name='43/430893/Cv/5'>cis-Aconitate</scene>
-Articles in Proteopedia concerning [[Citric Acid Cycle]] include:
+'''Step 2 - Hydration - Aconitase'''
-* [[Citrate_Synthase|Citrate Synthase Structure & Mechanism]]
 * [[Aconitase]]
-* [[Isocitrate dehydrogenase|Isocitrate Dehydrogenase]]
+*2nd step of [[Krebs cycle step 2]]
-* [[2-Oxoglutarate Dehydrogenase]] (also known as alpha-ketoglutarate dehydrogenase)
+C ''cis''-Aconitate => 6C <scene name='43/430893/Cv/6'>Isocitrate</scene>
-* [[Succinyl-CoA synthetase|Succinyl-CoA Synthetase]]
-* [[Succinate Dehydrogenase]]
+'''Step 3 - Oxidation - Isocitrate dehydrogenase'''
-* [[Fumarase]]
+*[[Isocitrate dehydrogenase]]
-* [[Malate dehydrogenase|Malate Dehydrogenase]]
+*1st step of [[Krebs cycle step 3]]
-* [[User:Cameron Evans/Sandbox 1|Glutamate Dehydrogenase]]
+C Isocitrate => 6C <scene name='43/430893/Cv/7'>Oxalosuccinate</scene>
-<br/>
+'''Step 4 - Decarboxylation - Isocitrate dehydrogenase'''
+*[[Isocitrate dehydrogenase]]
+*2nd step of [[Krebs cycle step 3]]
+C Oxalosuccinate => 5C <scene name='43/430893/Cv/8'>α-Ketoglutarate</scene>
-To view [[Citric Acid Cycle]] related proteins which are [[Proteopedia:Structure Index|Structure Index]] entries see:
+The α-ketoglutarate family of amino acid synthesis (synthesis of glutamate, glutamine, proline and arginine) begins with α-ketoglutarate, an intermediate in the Citric Acid Cycle. See [[Alpha-Ketoglutarates: glutamate, glutamine, proline, arginine]]
-* [[Aconitase#Available_3D_structures_of_Aconitase|Aconitase]]
-<br />
+'''Step 5 - Oxidative decarboxylation - α-Ketoglutarate dehydrogenase (2-Oxoglutarate Dehydrogenase)'''
+*[[2-Oxoglutarate Dehydrogenase]]
+*Step 5 = [[Krebs cycle step 4]]
+C α-Ketoglutarate => <scene name='43/430893/Cv/9'>Succinyl-CoA</scene> 4C chain (CoA excluded)
+'''Step 6 - Substrate-level phosphorylation - Succinyl-CoA synthetase'''
+*[[Succinyl-CoA synthetase]]
+*Step 6 = [[Krebs cycle step 5]]
+Succinyl-CoA => <scene name='43/430893/Cv/10'>Succinate</scene>
+The succinyl-CoA formed during [[Beta oxidation]] can also enter the Citric Acid Cycle in this step.
+'''Step 7 - Oxidation - Succinate dehydrogenase'''
+*[[Succinate Dehydrogenase]]
+*Step 7 = [[Krebs cycle step 6]]
+Succinate => <scene name='43/430893/Cv/11'>Fumarate</scene>
+'''Step 8 - Hydration - Fumarase'''
+*[[Fumarase]]
+*Step 8 = [[Krebs cycle step 7]]
+Fumarate => <scene name='43/430893/Cv/12'>L-Malate</scene>
+'''Step 9 - Oxidation - Malate dehydrogenase'''
+*[[Malate dehydrogenase]]
+*Step 9 = [[Krebs cycle step 8]]
+L-Malate => <scene name='43/430893/Cv/3'>oxaloacetate</scene>
+Oxaloacetate takes part in [[gluconeogenesis]], the urea cycle, the glyoxylate cycle, amino acid synthesis ([[Oxaloacetate/aspartate: lysine, asparagine, methionine, threonine, and isoleucine]]), [[fatty acid synthesis]].
+'''Step 10 / 0 - Aldol condensation - Citrate synthase'''
+*[[Citrate Synthase]]
+*Step 10 / 0 = [[Krebs cycle step 1]]
+C <scene name='43/430893/Cv/3'>oxaloacetate</scene> to a 6C molecule <scene name='43/430893/Cv/4'>citrate</scene>
 To view automatically seeded indices concerning [[Citric Acid Cycle]] See:
 *[[:Category:Citric acid cycle|Citric Acid Cycle]]
 <br />
+See also:
+*[[Biosynthesis of cholesterol]]
+*[[Fatty acid synthesis]]
+*[[Amino Acid Synthesis]]
 </StructureSection>