Citric acid cycle
A central metabolic pathway for energy release in respiration.
The citric acid cycle—also known as the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle—is a series of biochemical reactions that release the energy stored in nutrients through acetyl-CoA oxidation. The energy released is available in the form of ATP. The cycle is used by organisms that generate energy via respiration, either anaerobically or aerobically, and provides precursors of certain amino acids as well as the reducing agent NADH. Its central importance to many biochemical pathways suggests it was one of the earliest metabolic components.
- field
- Biochemistry
- known_for
- Citric acid cycle (Krebs cycle)
- discoverers
- Hans Adolf Krebs, William Arthur Johnson; also Carl Martius and Franz Knoop; components by Albert Szent-Györgyi
Lore & Background
He made this discovery by studying pigeon breast muscle, which maintains its oxidative capacity after breaking down in the Latapie mincer.
Reader's Guide
The citric acid cycle is a metabolic pathway that connects carbohydrate, fat, and protein metabolism. It completely oxidizes acetate in the form of acetyl-CoA into carbon dioxide, generating NADH, FADH2, and GTP or ATP. In eukaryotic cells, the cycle occurs in the mitochondrial matrix; in prokaryotic cells, it occurs in the cytosol. The cycle is not a fixed route—at least three alternative pathways are recognized. Its products feed into oxidative phosphorylation to produce ATP. The theoretical maximum yield of ATP from one glucose molecule via glycolysis, the citric acid cycle, and oxidative phosphorylation is estimated between 30 and 38, though inefficiencies such as proton leakage reduce this in eukaryotes. The cycle's role in anabolism means its intermediates are also used as precursors for biosynthesis.
Did You Know?
- The citric acid cycle is also called the Krebs cycle, Szent–Györgyi–Krebs cycle, or TCA cycle.
- For each pyruvate molecule, the cycle yields three NADH, one FADH2, and one GTP or ATP.
- In prokaryotic cells, the cycle occurs in the cytosol, with the proton gradient across the plasma membrane.
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