Citric acid cycle
Citric Acid Cycle
The Citric Acid Cycle (pronunciation: /ˈsɪtrɪk ˈæsɪd saɪkəl/), also known as the Krebs cycle or the tricarboxylic acid cycle (TCA 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.
Etymology
The Citric Acid Cycle is named after the type of acid that is consumed and then regenerated by this series of reactions to complete the cycle. The cycle is also known as the Krebs cycle, named after the British biochemist Sir Hans Adolf Krebs who identified the cycle's series of reactions in 1937.
Process
The Citric Acid Cycle begins with the reaction between Acetyl-CoA and the four-carbon oxaloacetate to form six-carbon citrate. The citrate then goes through a series of transformations, losing two carboxyl groups as CO2. The carbons lost as CO2 originate from what was oxaloacetate, not directly from acetyl-CoA. The carbons donated by acetyl-CoA become part of the oxaloacetate carbon backbone after the first turn of the citric acid cycle. Loss of the acetyl-CoA-donated carbons as CO2 requires several turns of the citric acid cycle. However, because of the role of the citric acid cycle in anabolism, they might not be lost since many TCA cycle intermediates are also used as precursors for the biosynthesis of other molecules.
Related Terms
- Acetyl-CoA: A molecule that participates in many biochemical reactions in protein, carbohydrate and lipid metabolism. Its main function is to deliver the acetyl group to the citric acid cycle to be oxidized for energy production.
- Oxaloacetate: A four-carbon molecule that combines with Acetyl-CoA to form citrate in the first step of the Citric Acid Cycle.
- Adenosine Triphosphate (ATP): The energy currency of life. It is the high-energy molecule that stores the energy we need to do just about everything we do.
- Carbon Dioxide: A colorless and odorless gas that is vital to life on Earth. It is produced during the Citric Acid Cycle.
External links
- Medical encyclopedia article on Citric acid cycle
- Wikipedia's article - Citric acid cycle
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