BackThe Urea Cycle definitions
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1/15BackSkip to main contentBackUrea Cycle
Cyclic pathway converting toxic ammonium ion into a less toxic compound for excretion, using ornithine as a carrier. Ornithine
Carrier molecule shuttling between mitochondria and cytosol, enabling the transfer of carbamoyl groups in the cycle. Carbamoyl Phosphate
High-energy intermediate formed from ammonium ion and carbon dioxide, initiating the cycle's reactions. Citrulline
Intermediate transported from mitochondria to cytosol, formed by transfer of a carbamoyl group to ornithine. Aspartate
Amino acid providing a nitrogen atom, condensing with citrulline to form argininosuccinate in the cycle. Argininosuccinate
Intermediate produced by condensation of citrulline and aspartate, later cleaved to yield arginine and fumarate. Arginine
Amino acid generated before the final step, hydrolyzed to produce urea and regenerate ornithine. Fumarate
Byproduct released during cleavage of argininosuccinate, linking the cycle to the citric acid cycle. Urea
Final, non-toxic nitrogenous waste product excreted in urine, formed from arginine hydrolysis. Carbamoyl Phosphate Synthetase
Mitochondrial enzyme catalyzing the energy-intensive synthesis of carbamoyl phosphate from ammonium ion and carbon dioxide. Ornithine Transcarbamylase
Enzyme catalyzing the transfer of a carbamoyl group to ornithine, forming citrulline in the mitochondria. Argininosuccinate Synthetase
Cytosolic enzyme catalyzing the ATP-dependent condensation of citrulline and aspartate to form argininosuccinate. Argininosuccinase
Enzyme responsible for cleaving argininosuccinate into arginine and fumarate during the cycle. Arginase
Cytosolic enzyme hydrolyzing arginine to regenerate ornithine and produce urea for excretion. Mitochondrial Matrix
Cellular compartment where the initial steps of the cycle occur, including carbamoyl phosphate synthesis.
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