citric acid cycle

step 0

pyruvate → acetyl-CoA

cofactors: CoA-SH + NAD+ → NADH + H+ ; TPP, Lipoate, FAD

enzyme: pyruvate dehydrogenase 

pyruvate structure

acetyl-CoA structure

citrate cycle net reaction

acetyl-CoA + 3NAD⁺ + FAD + GDP + P_i + 2H₂O → CoA + 2CO₂ + 3NADH + 3H⁺ + FADH₂ + GTP

rxn 1

acetyl-CoA + oxaloacetate → citrate

cofactors: H2O → CoA

enzyme: citrate synthase 

oxaloacetate structure

citrate structure

rxn 2

citrate → cis-aconitate → isocitrate

cofactors: H2O → ; → H2O

enzyme: aconitase 

cis-aconitate structure

isocitrate structure

rxn 3

isocitrate → oxalosuccinate → alpha-ketoglutarate 

cofactors: NAD⁺ → NADH + H⁺ ; → CO₂  and H⁺ →

_{enzyme: isocitrate dehydrogenase} 

oxalosuccinate structure 

alpha-ketoglutarate structure 

rnx 4

alpha-ketoglutarate → succinyl-CoA

cofactors: → CO₂; CoA → ; NAD⁺ → NADH + H⁺

enzyme: alpha-ketoglutarate dehydrogenase complex

succinyl-CoA structure 

rnx 5 

succinyl-CoA → Succinate 

cofactors: Pi → CoA ; GDP → GTP

enzyme: succinyl-CoA synthetase 

succinate structure 

rxn 6

succinate → fumarate 

cofactors: FAD → FADH₂

enzyme: succinate dehydrogenase 

fumarate structure 

rnx 7

fumarate → carbanion intermediate → malate

cofactors: OH^- → ; H⁺ →

enzyme: fumarase 

carbanion intermediate

malate structure 

rxn 8

malate → oxaloacetate

cofactors: NAD⁺ → NADH + H⁺

enzyme: malate dehydrogenase

oxaloacetate structure

substrates

pyruvate → (oxaloacetate) + acetyl-CoA → citrate → cis-aconitase → isocitrate → oxalosuccinate → alpha-ketoglutarate → succinyl-CoA → succinate → fumarate → carbanion intermediate → malate → oxaloacetate

step 0 net rxn

pyruvate + NAD+ CoA → Acetyl-CoA + CO2 + NADH + H+

enzymes

pyruvate dehydrogenase complex, citrate synthase, aconitase, isocitrate dehydrogenase, alpha-ketoglutarate dehydrogenase complex, succinyl-CoA synthetase, succinate dehydrogenase, fumarase, malate dehydrogenase

regulated steps

1, 3, 4

energy producing steps

0: NADH

3: NADH

4: NADH

5: GTP

6: FADH2

8: NADH