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Tricarboxylic acid cycle

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(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).


The tricarboxylic acid cycle is an alternative name for Krebs cycle, which was first described by Hans Adolf Krebs in 1937. It is called tricarboxylic acid cycle because the citric acid is both the first product and the final reactant, and it contains three carboxyl groups.

Also called: citric acid cycle, Krebs cycle.
See also: glycolysis, oxidative phosphorylation, cellular respiration.