Citric Acid Cycle Intermediates in Order: Carbons, Enzymes, NADH and FADH2

Use this as a one-glance table of the cycle. Citrate and isocitrate each have 6 carbons, and succinate has 4.

The cycle in order

Totals per turn

Each turn gives 3 NADH, 1 FADH₂, 1 GTP and 2 CO₂. Per glucose, the cycle runs twice, so double each number.

Memory aids

• The two CO₂ leave at isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase, which is why the carbons drop from 6 to 4.
• Succinate dehydrogenase is the only cycle enzyme embedded in the inner mitochondrial membrane (complex II).

Common traps

• Giving succinate 5 carbons.
• Saying FADH₂ comes from malate dehydrogenase. It is succinate dehydrogenase.
• Forgetting the doubling per glucose.

One-minute recap

• 6, 6, 5, 4, 4, 4, 4, 4 carbons around the loop.
• CO₂ twice, NADH three times, FADH₂ once, GTP once.