Urea

Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula C O N₂H₄ and the structure (yooē´e) , organic compound that is the principal end product of nitrogen metabolism in most mammals. Urea was the first animal metabolite to be isolated in crystalline form; its crystallization was described in the early 18th cent., and in 1773 it was noted that urea gave off ammonia when heated. This discovery provided a clue to its structure. In 1828 urea also became the first organic compound to be synthesized from inorganic materials (lead or silver cyanate and ammonia); this work was done by German chemist Friedrich Wöhler in 1828.

Years of investigation of the biosynthesis of urea culminated in the proposal of the ornithine cycle (sometimes known as the Krebs urea cycle, named for German-born chemist Hans Krebs) in 1932. The proposed cycle has since been amended only in detail. It involves the linking of one molecule of ammonia with one molecule of carbon dioxide to form carbamoyl phosphate which then is added to ornithine resulting in the formation of citrulline. Next the nitrogen-containing amino group from aspartic acid is combined with the citrulline, resulting in the formation of arginine .

The addition of a water molecule, arginine is then split into one molecule of urea and one molecule of ornithine, which can now repeat the cycle. In metabolism of proteins and other materials, the ammonia molecule that enters the cycle originates from glutamic acid, but glutamic acid can acquire the group that generates this ammonia from many other amino acids; thus most of the nitrogen in protein can eventually be converted to nitrogen in urea.

These reactions have been shown to occur in the liver. Urea is transported in the blood to the kidneys, where it is filtered out; its concentration in urine is about 60 to 70 times as great as that in blood. Terrestrial animals produce urea from carbon dioxide and ammonia in the urea cycle, an anabolic process. This expenditure of energy is necessary because ammonia, a common metabolic waste product, is toxic and must be neutralized. Aquatic animals do not produce urea; living in an abundant supply of water, they can simply excrete ammonia immediately as it is produced. Birds, with more severe restrictions on water consumption than most other terrestrial creatures, produce uric acid, a compound even less toxic than urea.

Discovery
Urea was discovered by Hilaire Rouelle in 1773. It was the first organic compound to be artificially synthesised in 1828 by Friedrich Woehler, who prepared it by the reaction of potassium cyanate with ammonium sulfate. This disproved the theory that the chemicals of living organisms are substantially different from inanimate matter and started the discipline of organic chemistry.

Industrial Use
Its principal industrial use is the manufacture of plastics (specifically, urea-formaldehyde resin).

It is also a component of many fertilisers, providing a nitrogen source that is necessary for plants.

Laboratory Use
Urea is a powerful protein denaturant. This property can be exploited to help solubilize proteins that do not go into solution easily. For this application it is used in concentrations up to 6M.

Medical Significance
Because urea is produced and excreted at a roughly constant rate, high levels of urea in the blood indicate a problem with the removal, or more rarely with the over-production, of urea in the body.

The most common cause of uremia is renal problems. It is measured along with creatinine to indicate direct problems with the kidneys (e.g. chronic renal failure) or secondary problems such as hypothyroidism.

Urea levels can also be increased in some malignant blood disorders, (e.g. leukaemia and multiple myeloma).

Markedly high levels of urea (uremia) can cause neurological disturbances. Prolonged periods of uremia may result in the skin taking on a grey discoloration.

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Urea Urea is an organic compound of carbon, nitrogen, oxygen and hydrogen, with the formula C O N₂H₄ and the structure (yooē´e) , organic compound that is the principal end product of nitrogen metabolism in most mammals. Urea was the first animal metabolite to be isolated in crystalline form; its crystallization was described in the early 18th cent., and in 1773 it was noted that urea gave off ammonia when heated. This discovery provided a clue to its structure. In 1828 urea also became the first organic compound to be synthesized from inorganic materials (lead or silver cyanate and ammonia); this work was done by German chemist Friedrich Wöhler in 1828. Years of investigation of the biosynthesis of urea culminated in the proposal of the ornithine cycle (sometimes known as the Krebs urea cycle, named for German-born chemist Hans Krebs) in 1932. The proposed cycle has since been amended only in detail. It involves the linking of one molecule of ammonia with one molecule of carbon dioxide to form carbamoyl phosphate which then is added to ornithine resulting in the formation of citrulline. Next the nitrogen-containing amino group from aspartic acid is combined with the citrulline, resulting in the formation of arginine . The addition of a water molecule, arginine is then split into one molecule of urea and one molecule of ornithine, which can now repeat the cycle. In metabolism of proteins and other materials, the ammonia molecule that enters the cycle originates from glutamic acid, but glutamic acid can acquire the group that generates this ammonia from many other amino acids; thus most of the nitrogen in protein can eventually be converted to nitrogen in urea. These reactions have been shown to occur in the liver. Urea is transported in the blood to the kidneys, where it is filtered out; its concentration in urine is about 60 to 70 times as great as that in blood. Terrestrial animals produce urea from carbon dioxide and ammonia in the urea cycle, an anabolic process. This expenditure of energy is necessary because ammonia, a common metabolic waste product, is toxic and must be neutralized. Aquatic animals do not produce urea; living in an abundant supply of water, they can simply excrete ammonia immediately as it is produced. Birds, with more severe restrictions on water consumption than most other terrestrial creatures, produce uric acid, a compound even less toxic than urea. Discovery Urea was discovered by Hilaire Rouelle in 1773. It was the first organic compound to be artificially synthesised in 1828 by Friedrich Woehler, who prepared it by the reaction of potassium cyanate with ammonium sulfate. This disproved the theory that the chemicals of living organisms are substantially different from inanimate matter and started the discipline of organic chemistry. Industrial Use Its principal industrial use is the manufacture of plastics (specifically, urea-formaldehyde resin). It is also a component of many fertilisers, providing a nitrogen source that is necessary for plants. Laboratory Use Urea is a powerful protein denaturant. This property can be exploited to help solubilize proteins that do not go into solution easily. For this application it is used in concentrations up to 6M. Medical Significance Because urea is produced and excreted at a roughly constant rate, high levels of urea in the blood indicate a problem with the removal, or more rarely with the over-production, of urea in the body. The most common cause of uremia is renal problems. It is measured along with creatinine to indicate direct problems with the kidneys (e.g. chronic renal failure) or secondary problems such as hypothyroidism. Urea levels can also be increased in some malignant blood disorders, (e.g. leukaemia and multiple myeloma). Markedly high levels of urea (uremia) can cause neurological disturbances. Prolonged periods of uremia may result in the skin taking on a grey discoloration. Other links to pertinent articles: Urea cycle Articles and Information Modeling Urea Processes: A Ne w Thermodynamic Model and Software Integration Paradigm Britannica Concise Encyclopedia Online Article NATIONAL UREA CYCLE DISORDERS FOUNDATION <<Back to Article Index Protect Your Business from lawsuits with Icenator
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Urea

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