The urea cycle, also known as the ornithine cycle, is a series of biochemical reactions that occur in the liver. It converts toxic ammonia, which is a byproduct of protein metabolism, into a less toxic form called urea. Urea can then be safely transported in the blood and excreted by the kidneys in urine. The urea cycle involves five main enzymes that catalyze the reactions in the cycle. Here is a step-by-step description of the urea cycle and the enzymes involved:1. Carbamoyl phosphate synthetase I CPS1 : The first step in the urea cycle is the formation of carbamoyl phosphate from ammonia and bicarbonate. This reaction is catalyzed by the enzyme carbamoyl phosphate synthetase I CPS1 and requires the input of two molecules of ATP.2. Ornithine transcarbamylase OTC : Carbamoyl phosphate then reacts with the amino acid ornithine to form citrulline. This reaction is catalyzed by the enzyme ornithine transcarbamylase OTC .3. Argininosuccinate synthetase ASS : In the next step, citrulline reacts with another amino acid, aspartate, to form argininosuccinate. This reaction is catalyzed by the enzyme argininosuccinate synthetase ASS and requires the input of one molecule of ATP.4. Argininosuccinate lyase ASL : Argininosuccinate is then cleaved by the enzyme argininosuccinate lyase ASL to produce the amino acid arginine and fumarate. Fumarate can be converted to malate and enter the citric acid cycle to generate energy.5. Arginase ARG1 : The final step in the urea cycle is the hydrolysis of arginine to produce urea and regenerate ornithine. This reaction is catalyzed by the enzyme arginase ARG1 . Ornithine is then transported back into the mitochondria to start the cycle again.In summary, the urea cycle converts toxic ammonia into a less toxic form, urea, through a series of reactions catalyzed by five enzymes: carbamoyl phosphate synthetase I CPS1 , ornithine transcarbamylase OTC , argininosuccinate synthetase ASS , argininosuccinate lyase ASL , and arginase ARG1 . Urea is then excreted by the kidneys, effectively removing ammonia from the body.