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From Wikipedia, the free encyclopedia. The urea cycle (also known as the ornithine cycle) is a cycle of biochemical reactions occurring in many animals that produces urea ((NH2)2CO) from ammonia (NH3). This cycle was the first metabolic cycle discovered (Hans Krebs and Kurt Henseleit, 1932), five years before the discovery of the TCA cycle. In mammals, the urea cycle takes place primarily in the liver, and to a lesser extent in the kidney.
Urea is synthesized in the body of many organisms as part of the urea cycle, either from the oxidation of amino acids or from ammonia. In this cycle, amino groups donated by ammonia and L-aspartate are converted to urea, while L-ornithine, citrulline, L-argininosuccinate, and L-arginine act as intermediates.rea is widely used in fertilizers as a source of nitrogen and is an important raw material for the chemical industry. Friedrich Woehler 'wÃ¶hler s discovery in 1828 that urea can be produced from inorganic starting materials was an important conceptual milestone in. chemistry