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Definition

noun

(1) A cycle of reactions catalyzed by enzymes in which pyruvate derived from nutrients and converted to Acetyl Coenzyme A is completely oxidized and broken down into carbon dioxide and water to produce high-energy phosphate compounds, which are the source of cellular energy.

(2) One of the major metabolic pathways of cellular respiration, and involves a cyclic series of enzymatic reactions by which pyruvate converted into Acetyl Coenzyme A is completely oxidized to CO₂ and hydrogen is removed from the carbon molecules, transferring the hydrogen atoms and electrons to electron-carrier molecules (e.g. NADH and FADH₂) as well as the metabolic energy to high energy bonds (e.g. ATP).

Supplement

Krebs cycle is named after Hans Krebs, a British biochemist who identified it. It was also named Szent-Györgyi-Krebs cycle (although rare), after Albert Szent-Györgyi de Nagyrápolt who identified fumaric acid and other steps in what would become known as the Krebs cycle.

The Krebs cycle is the stage of cellular respiration following glycolysis and decarboxylation of pyruvate. The carbon dioxide produced from the complete oxidation of pyruvate is removed from the cell into the blood. The electron and hydrogen carriers, NADH and FADH₂, donate these electrons to the electron transport chain to generate ATP via oxidative phosphorylation, the final metabolic pathway of cellular respiration.

In eukaryotes the Krebs Cycle occurs in the matrix of the mitochondrion whereas in prokaryotes, it occurs in the cytoplasm.

Word origin: named after Hans Adolf Krebs, first described it in 1937.

Also called: citric acid cycle, tricarboxylic acid cycle (TCA cycle).
See also: glycolysis, oxidative phosphorylation, cellular respiration.