TCA cycle

TCA cycle (also known as the Citric Acid Cycle or the Krebs Cycle) is a series of chemical reactions used by all aerobic organisms to release stored energy through the oxidation of acetyl-CoA derived from carbohydrates, fats, and proteins into adenosine triphosphate (ATP) and carbon dioxide.

Overview

The TCA cycle is the second stage of cellular respiration, the three-stage process by which cells convert nutrients into energy and other necessary materials. The cycle includes eight major steps that occur within the mitochondrion of the cell. The cycle is named after Hans Krebs, who identified the series of reactions in 1937.

Steps of the TCA Cycle

The TCA cycle consists of eight steps:

1. Citrate synthesis: Acetyl CoA combines with oxaloacetate to form citrate.
2. Isomerization: Citrate is rearranged to form isocitrate.
3. Oxidative decarboxylation: Isocitrate is oxidized and decarboxylated to form alpha-ketoglutarate.
4. Second oxidative decarboxylation: Alpha-ketoglutarate is further oxidized and decarboxylated to form succinyl CoA.
5. Substrate-level phosphorylation: Succinyl CoA is converted into succinate.
6. Oxidation: Succinate is oxidized to form fumarate.
7. Hydration: Fumarate is hydrated to form malate.
8. Regeneration of oxaloacetate: Malate is oxidized to regenerate oxaloacetate.

Regulation

The TCA cycle is regulated mainly by product inhibition and substrate availability. The key control points are the enzymes isocitrate dehydrogenase and alpha-ketoglutarate dehydrogenase.

Clinical significance

Defects in the TCA cycle can lead to a variety of metabolic disorders, including diabetes, cancer, and neurodegenerative diseases.

See also

• Cellular respiration
• Glycolysis
• Oxidative phosphorylation

References

TCA cycle Resources
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