Question

The enzyme ____________ is the regulated and committing step to urea synthesis

Answer 1

Answer: a) Carbamoyl phosphate synthetase I  

Explanation:

The set of reactions of converting ammonia to urea for its elimination makes up what we call the urea cycle. This cycle occurs in liver cells and, in simplified form, consists of 5 steps. In the first step we have the  carbamoyl phosphate synthesis. Urea synthesis begins in the mitochondrial matrix by condensing carbon dioxide (CO2) with ammonia (NH3), the primary source of nitrogen, using ATP to form the compound called carbamoyl phosphate. This process is performed with the help of the enzyme Carbamoyl phosphate synthetase I,  the regulated and committing step to urea synthesis.

In the 2nd stage: carbamoyl phosphate plus ornithine form citrulline, in the 3rd stage: citrulline plus aspartate form arginosuccinate, 4th reaction: breakage of arginine succinate forms arginine and fumarate and Step 5: Breaking arginine releases urea and regenerates ornithine