Question

Please describe the reaction catalyzed by carbamoyl phosphate synthetase I, including substrates, products, and high-energy bonds consumed. In what subcellular location does this reaction occur?

a) Carbamoyl phosphate synthetase I converts carbamoyl phosphate to ornithine in the mitochondria.
b) Carbamoyl phosphate synthetase I converts ammonia and bicarbonate to carbamoyl phosphate in the cytoplasm.
c) Carbamoyl phosphate synthetase I converts carbamoyl phosphate to citrulline in the endoplasmic reticulum.
d) Carbamoyl phosphate synthetase I converts ornithine to citrulline in the lysosomes.

Answer 1

Carbamoyl phosphate synthetase I catalyzes the formation of carbamoyl phosphate from ammonia and bicarbonate, consuming two ATP molecules in the mitochondria. This is the initial step of the urea cycle.

Step-by-step explanation:

The reaction catalyzed by carbamoyl phosphate synthetase I (CPS-1) involves the conversion of ammonia and bicarbonate into carbamoyl phosphate, with the consumption of two molecules of ATP. The substrates for this enzyme are ammonia (NH3), bicarbonate (HCO3-), and ATP, while the products are carbamoyl phosphate and ADP. The reaction occurs in the mitochondria and represents the first step of the urea cycle. The carbamoyl phosphate then enters subsequent reactions within the urea cycle, including its combination with ornithine to produce citrulline, a process catalyzed by the enzyme ornithine transcarbamylase within the mitochondria.