Question

Choose the correct sequence :

• A. carbamoyl phosphate - citrulline - arginine & fumarate - urea & ornithine
• B. carbamoyl phosphate - citrulline - urea & ornithine - arginine & fumarate
• C. arginine & fumarate - carbamoyl phosphate - citrulline - urea & ornithine
• D. arginine & fumarate - citrulline - urea & ornithine - carbamoyl phosphate

Answer 1

The correct option is A carbamoyl phosphate - citrulline - arginine & fumarate - urea & ornithine

The conversion from ammonia to urea happens in five main steps.
1. Ammonia is converted to carbamoyl phosphate. This reaction requires two ATP molecules, which are converted to two ADP molecules.
2. Carbamoyl phosphate is converted to citrulline.
3. Aspartate and citrulline react to form an intermediate. This reaction requires one ATP molecule, which is converted to AMP.
4. Next, arginine and fumarate are formed.
5. Arginine is cleaved to form urea and ornithine. The ornithine begins the urea cycle again and urea is released out of the body through urine.