Translations:Citric acid cycle/10/en: Difference between revisions

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Message definition (Citric acid cycle)
== Steps ==
There are ten basic steps in the citric acid cycle, as outlined below. The cycle is continuously supplied with new carbon in the form of [[acetyl-CoA]], entering at step 0 in the table.
{| class="wikitable"
!
!Reaction type
!Substrates
!Enzyme
!Products
!Comment
|-
|{{nowrap|0 / 10}}
|[[Aldol condensation]]
|[[Oxaloacetic acid|Oxaloacetate]] + [[Acetyl CoA]] + H<sub>2</sub>O
|[[Citrate synthase]]
|[[Citric acid|Citrate]] + [[Coenzyme A|CoA-SH]]
|irreversible, extends the 4C [[Oxaloacetic acid|oxaloacetate]] to a 6C molecule
|-
|1
| [[Dehydration reaction|Dehydration]]
|[[Citrate]]
| rowspan="2" |[[Aconitase]]
|''[[Cis–trans isomerism|cis]]''-[[Aconitic acid|Aconitate]] + H<sub>2</sub>O
|rowspan=2|reversible [[Isomerization|isomerisation]]
|-
|2
|[[Hydration reaction|Hydration]]
|[[Aconitate|''cis''-Aconitate]] + H<sub>2</sub>O
|[[Isocitric acid|Isocitrate]]
|-
|3
|[[Oxidation]]
|[[Isocitrate]] + [[Nicotinamide adenine dinucleotide|NAD]]<sup>+</sup>
| rowspan="2" |[[Isocitrate dehydrogenase]]
|[[Oxalosuccinic acid|Oxalosuccinate]] + [[Nicotinamide adenine dinucleotide|NADH + H <sup>+</sup>]]
|generates [[NADH]] (equivalent of 2.5 ATP)
|-
|4
|[[Decarboxylation]]
|[[Oxalosuccinate]]
|[[alpha-Ketoglutaric acid|α-Ketoglutarate]] + CO<sub>2</sub>
|rate-limiting, irreversible stage, generates a 5C molecule
|-
|5
|Oxidative<br />[[decarboxylation]]
|[[alpha-Ketoglutaric acid|α-Ketoglutarate]] + NAD<sup>+</sup> + CoA-SH
|[[Alpha-ketoglutarate dehydrogenase|α-Ketoglutarate<br />dehydrogenase]], [[Thiamine pyrophosphate]], [[Lipoic acid]], Mg++,transsuccinytase
|[[Succinyl-CoA]] + [[Nicotinamide adenine dinucleotide|NADH + H <sup>+</sup>]] + CO<sub>2</sub>
|irreversible stage, generates [[Nicotinamide adenine dinucleotide|NADH]] (equivalent of 2.5 ATP), regenerates the 4C chain (CoA excluded)
|-
|6
|[[substrate-level phosphorylation|substrate-level<br />phosphorylation]]
|[[Succinyl-CoA]] + [[Guanosine diphosphate|GDP]] + [[Inorganic phosphate|P<sub>i</sub>]]
|[[Succinyl coenzyme A synthetase|Succinyl-CoA synthetase]]
|[[Succinic acid|Succinate]] + CoA-SH + [[Guanosine triphosphate|GTP]]
|or [[adenosine diphosphate|ADP]]→[[adenosine triphosphate|ATP]] instead of GDP→GTP, generates 1 ATP or equivalent.<br />[[Condensation reaction]] of [[Guanosine diphosphate|GDP]] + [[Inorganic phosphate|P<sub>i</sub>]] and [[hydrolysis]] of [[succinyl-CoA]] involve the H<sub>2</sub>O needed for balanced equation.
|-
|7
|[[Redox|Oxidation]]
|[[Succinate]] + [[ubiquinone]] (Q)
|[[Succinate dehydrogenase]]
|[[Fumaric acid|Fumarate]] + [[ubiquinol]] (QH<sub>2</sub>)
|uses [[Flavin adenine dinucleotide|FAD]] as a [[prosthetic group]] (FAD→FADH<sub>2</sub> in the first step of the reaction) in the enzyme.<br />These two electrons are later transferred to QH<sub>2</sub> during Complex II of the ETC, where they generate the equivalent of 1.5 ATP
|-
|8
|[[Hydration reaction|Hydration]]
|[[Fumarate]] + H<sub>2</sub>O
|[[Fumarase]]
|''L''-[[Malic acid|Malate]]
|Hydration of C-C double bond
|-
|9
|[[Redox|Oxidation]]
|[[Malate|<small>L</small>-Malate]] + NAD<sup>+</sup>
|[[Malate dehydrogenase]]
|[[Oxaloacetate]] + NADH + H<sup>+</sup>
|reversible (in fact, equilibrium favors malate), generates [[NADH]] (equivalent of 2.5 ATP)
|-
|10 / 0
|[[Aldol condensation]]
|[[Oxaloacetic acid|Oxaloacetate]] + [[Acetyl CoA]] + H<sub>2</sub>O
|[[Citrate synthase]]
|[[Citric acid|Citrate]] + [[Coenzyme A|CoA-SH]]
|This is the same as step 0 and restarts the cycle. The reaction is irreversible and extends the 4C oxaloacetate to a 6C molecule
|}

Steps

There are ten basic steps in the citric acid cycle, as outlined below. The cycle is continuously supplied with new carbon in the form of acetyl-CoA, entering at step 0 in the table.

Reaction type Substrates Enzyme Products Comment
0 / 10 Aldol condensation Oxaloacetate + Acetyl CoA + H2O Citrate synthase Citrate + CoA-SH irreversible, extends the 4C oxaloacetate to a 6C molecule
1 Dehydration Citrate Aconitase cis-Aconitate + H2O reversible isomerisation
2 Hydration cis-Aconitate + H2O Isocitrate
3 Oxidation Isocitrate + NAD+ Isocitrate dehydrogenase Oxalosuccinate + NADH + H + generates NADH (equivalent of 2.5 ATP)
4 Decarboxylation Oxalosuccinate α-Ketoglutarate + CO2 rate-limiting, irreversible stage, generates a 5C molecule
5 Oxidative
decarboxylation 		α-Ketoglutarate + NAD+ + CoA-SH α-Ketoglutarate
dehydrogenase, Thiamine pyrophosphate, Lipoic acid, Mg++,transsuccinytase 		Succinyl-CoA + NADH + H + + CO2 irreversible stage, generates NADH (equivalent of 2.5 ATP), regenerates the 4C chain (CoA excluded)
6 substrate-level
phosphorylation 		Succinyl-CoA + GDP + Pi Succinyl-CoA synthetase Succinate + CoA-SH + GTP or ADP→ATP instead of GDP→GTP, generates 1 ATP or equivalent.
Condensation reaction of GDP + Pi and hydrolysis of succinyl-CoA involve the H2O needed for balanced equation.
7 Oxidation Succinate + ubiquinone (Q) Succinate dehydrogenase Fumarate + ubiquinol (QH2) uses FAD as a prosthetic group (FAD→FADH2 in the first step of the reaction) in the enzyme.
These two electrons are later transferred to QH2 during Complex II of the ETC, where they generate the equivalent of 1.5 ATP
8 Hydration Fumarate + H2O Fumarase L-Malate Hydration of C-C double bond
9 Oxidation L-Malate + NAD+ Malate dehydrogenase Oxaloacetate + NADH + H+ reversible (in fact, equilibrium favors malate), generates NADH (equivalent of 2.5 ATP)
10 / 0 Aldol condensation Oxaloacetate + Acetyl CoA + H2O Citrate synthase Citrate + CoA-SH This is the same as step 0 and restarts the cycle. The reaction is irreversible and extends the 4C oxaloacetate to a 6C molecule
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