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map00020                    Pathway                                

Citrate cycle (TCA cycle)
The citrate cycle (TCA cycle, Krebs cycle) is an important aerobic pathway for the final steps of the oxidation of carbohydrates and fatty acids. The cycle starts with acetyl-CoA, the activated form of acetate, derived from glycolysis and pyruvate oxidation for carbohydrates and from beta oxidation of fatty acids. The two-carbon acetyl group in acetyl-CoA is transferred to the four-carbon compound of oxaloacetate to form the six-carbon compound of citrate. In a series of reactions two carbons in citrate are oxidized to CO2 and the reaction pathway supplies NADH for use in the oxidative phosphorylation and other metabolic processes. The pathway also supplies important precursor metabolites including 2-oxoglutarate. At the end of the cycle the remaining four-carbon part is transformed back to oxaloacetate. According to the genome sequence data, many organisms seem to lack genes for the full cycle [MD:M00009], but contain genes for specific segments [MD:M00010 M00011].
Metabolism; Carbohydrate metabolism
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map00020  Citrate cycle (TCA cycle)

Ortholog table
M00003  Gluconeogenesis, oxaloacetate => fructose-6P [PATH:map00020]
M00009  Citrate cycle (TCA cycle, Krebs cycle) [PATH:map00020]
M00010  Citrate cycle, first carbon oxidation, oxaloacetate => 2-oxoglutarate [PATH:map00020]
M00011  Citrate cycle, second carbon oxidation, 2-oxoglutarate => oxaloacetate [PATH:map00020]
M00307  Pyruvate oxidation, pyruvate => acetyl-CoA [PATH:map00020]
M00740  Methylaspartate cycle [PATH:map00020]
H00073  Pyruvate carboxylase deficiency
H00469  Mitochondrial DNA depletion syndrome
H00804  Multiple cutaneous and uterine leiomyomata
H01022  Diseases of the tricarboxylic acid cycle
H01225  D-2-hydroxyglutaric aciduria
H02000  Dihydrolipoamide dehydrogenase deficiency
H02004  Fumarase deficiency
H02005  Mitochondrial complex II deficiency
H02006  Alpha-ketoglutarate dehydrogenase complex deficiency
H02113  Infantile cerebellar-retinal degeneration
Other DBs
GO: 0006099
(map 2)
Nishizuka Y (ed).
[Metabolic Maps] (In Japanese)
Tokyo Kagaku Dojin (1980)
(map 3)
Nishizuka Y, Seyama Y, Ikai A, Ishimura Y, Kawaguchi A (eds).
[Cellular Functions and Metabolic Maps] (In Japanese)
Tokyo Kagaku Dojin (1997)
Michal G.
Biochemical Pathways
Wiley (1999)
KO pathway

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