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The cycle happens once for every pyruvate molecule (3 Carbons) so a glucose molecule (6 Carbons) results in 2 cycles.
1. Citrate synthase catalyses the reaction of Acetyl CoA (2C) with oxaloacetate (4C) to form citrate (citric acid - 6C)
During step one, Coenzyme A breaks off to be used in the link reaction again
2. Decarboxylation: the citrate (6C) is converted to a 5C molecule so CO2 is given off
and Dehydrogenation: hydrogen is removed and used to reduce NAD. The product is a 5C molecule
3. The 5C molecule undergoes decarboxylation and dehydrogenation resulting in a 4C molecule. This time, one molecule of reduced FAD and two molecules of reduced NAD are created from a series of intermediate reactions converting the 5C to 4C.
4. ATP is produced from direct transfer of a phosphate group from an intermediate compound to ADP during step four. This is called substrate-level phosphorylation.
The resulting 4C compound is oxaloacetate so the cycle continues in the same way, creating reduced coenzymes and ATP.
Total products from Krebs cycle:
1 coenzyme A
3 reduced NAD
1 reduced FAD