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Pyruvate's Key Reactions & Pathways
- 1. Pyruvate Reactions Three pathways
- 2. Formation of Acetyl CoAAerobic Conditions Citric acid cycle starting point Building block for fatty acid biosynthesis
- 3. Formation of Acetyl CoA Thioester
- 4. Formation of Acetyl CoAAerobic Conditions
- 5. Formation of LactateAnaerobic Conditions Oh, those aching muscles!
- 6. Formation of LactateAnaerobic Conditions Lactate dehydrogenase
- 10. Energy generation: 2 ATP from glycolysis
Editor's Notes
- There are three possible pathways for pyruvate formed from glycolysis.
- Under aerobic conditions (in the presence of oxygen) pyruvate forms acetyl CoA (structure shown).Acetyl CoA is the starting point of the citric acid cycle.It is also a building block for fatty acid biosynthesis. All naturally occurring fatty acids contain even number of carbons because they are made from the two carbons of Acetyl CoA.
- Abbreviate and complete structures of acetyl CoA are shown.Acetyl CoA is a thioester. Thioesters are much more reactive than oxygen esters.
- Pyruvate reaction shown.Pyruvate reacts with NAD+ and coenzyme A to form acetyl CoA. The reaction is catalyzed by pyruvate dehydrogenase complex.Pyruvate is split apart, oxidation forming CO2. NAD+ is reduced, gaining hydrogen.Oxygen is not present in this reaction or in the following citric acid cycle.Oxygen is required in the electron transport chain to complete the regeneration of NAD+ from NADH.Without oxygen, pyruvate must take one of the other pathways.,
- Under anaerobic conditions (absence of oxygne), pyruvate forms lactate.When exercising, it is the build up of lactate that causes sore muscles.
- In the absence of oxygen.Pyruvate is reduced by NADH to form lactate and NAD+.
- Yeast has an alternate pathway of anaerobic pyruvate metabolism.Pyruvate is decarboxylated to form acetaldehyde.The NAD+ produced may be used in the glycolysis reaction.Acetaldehyde is reduced by NADH to form ethanol and NAD+
- For anaerobic organisms, the ATP generated by glycolysis sustains life.In humans under anaerobic conditions, ATP from glycolysis furnishes energy when oxygen is insufficient for ATP generation by complete oxidation of pyurvate.