Question

Which of the following statement/statements are not true according to urea cycle?
I. Two ATP molecules are required for synthesis of carbamoyl phosphate.
II. Products of urea cycle are: 1 molecule of urea, 2 molecules of ADP, 1 molecule each of AMP and fumaric acid.
III. Urea cycle takes place in kidney cells.
IV. Reaction of citrulline and aspartate requires ATP.

• A. I, III, and IV only
• B. I and III only
• C. I, II, and IV only
• D. III only

Answer 1

The correct option is D III only

Nitrogen excreted by the humans and mammals is in the form of urea. It is produced through a series of reactions occurring in the cytosol and mitochondrial matrix of liver cells. These reactions are collectively called the urea cycle.
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.
Products of urea cycle are: 1 molecule of urea, 2 molecules of ADP, 1 molecule of both AMP and fumaric acid.