1. Pyruvate Oxidation The Citric Acid Cycle
Aerobic Respiration
Pyruvate Oxidation
The Citric Acid Cycle

2. What happens to pyruvate?
depends on whether oxygen is present (aerobic respiration) or not (anaerobic respiration)
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3. Pyruvate Oxidation
if oxygen is present, the pyruvate molecules are transported from the cytoplasm into the mitochondrial matrix
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4. Pyruvate Oxidation
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5. Pyruvate Oxidation 3 enzyme-catalyzed changes:
decarboxylation forming CO2 as a by-product
oxidation of the 2-carbon molecule, causing a reduction of NAD+ to NADH
attachment of coenzyme A (a derivative of vitamin B5), forming acetyl-CoA

6. Pyruvate Oxidation
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7. (Also known as the Krebs Cycle)
The Citric Acid Cycle
(Also known as the Krebs Cycle) 7

8. The Citric Acid Cycle 8 enzyme-catalyzed reactions
occurs in the mitochondrial matrix
aerobic process
cyclic process: oxaloacetate is the reactant of the first reaction and product of the last reaction

9. First reaction
acetyl CoA (2C) reacts with oxaloacetate (4C) to produce citrate (6C)
CoA is released

10. Citric Acid Cycle Pathway
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11. Major Processes: Decarboxylation (Reactions 3 & 4)
2 different reactions involve the removal of carbon as CO2

12. Major Processes: Oxidation (Reactions 3, 4, 6, 8)
H atoms (with their associated electrons) are transferred to a coenzyme (NAD+ or FAD)

13. Major Processes: Energy Production (Reaction 5)
during one of the reactions, ATP is generated by substrate-level phosphorylation.
it is coupled to a reaction which has a large amount of free energy release

14. Summary oxaloacetate is regenerated in the last step
all 6 carbons from glucose have been oxidized to CO2
all of the energy from glucose is in the form of ATP, NADH and FADH2

15. Krebs Cycle Overall Reaction
2 acetyl CoA + 6NAD+ + 2 FAD + 2ADP + 2 Pi
4 CO2 + 6 NADH + 6 H+ + 2 FADH2 + 2 ATP 15

16. Summary
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17. Animations
Simple reaction review:
Animation & Quiz: 17

18. Preview of ETC…
If you’re confused about the Electron Transport Chain, this animation might help: