Krebs Cycle

The Krebs cycle, also called the citric acid cycle or the tricarboxylic acid cycle, is a closed loop of linked chemical reactions that takes place in the mitochondria of nearly all living cells and completes the oxidation of the carbon compounds derived from food, releasing the energy cells store as ATP and generating the carbon dioxide organisms exhale. Hans Krebs worked it out in 1937 at the University of Sheffield with William Arthur Johnson, building on his own earlier 1932 discovery, made at Freiburg with Kurt Henseleit, of the related urea cycle by which the body disposes of toxic ammonia. The pair first submitted the finding to the journal Nature, which rejected it as too long; it was published instead in the smaller journal Enzymologia the same year. The cycle sits at the hub of cellular metabolism, the point where the breakdown products of carbohydrates, fats and proteins all converge to be oxidized by the same shared pathway, and its discovery is considered one of the foundational achievements of twentieth-century biochemistry. Krebs shared the 1953 Nobel Prize in Physiology or Medicine with Fritz Lipmann, who discovered coenzyme A, a molecule the cycle depends on to carry the acetyl groups that feed into it.