Citric Acid Cycle

Cataplerotic reactions

Deplete the components of the cycle

• Products are consumed in other pathways

Anaplerotic reactions

Replenish the components of the cycle

• Products from other pathways are converted to substrates of the cycle

Step 1:

Oxaloacetate → Citrate

This is a very exergonic reaction due to the hydrolysis of the acetyl-CoA thioester

Step 2:

Citrate → Isocitrate

Step 3:

Isocitrate → α-Ketoglutarate

Step 4:

a-ketoglutarate → succinyl-CoA

Enzyme: α-Ketoglutarate dehydrogenase

Step 5:

Succinyl-CoA → Succinate

This is the only substrate-level phosphorylation reaction of the cycle

(right to left in pic)

Step 6:

Succinate → Fumarate

(right to left in pic)

Step 7:

Fumarate → Malate

Step 8:

Malate → Oxaloacetate