Question

In ornithine cycle, number of ATP molecules spent to convert toxic ammonia to a molecular urea is

• A. Four
• B. Two
• C. Three
• D. One

Answer 1

Answer: (C)

Three

The ornithine cycle is carried out in the liver of certain organisms. This cycle is responsible for the conversion of the toxic form of nitrogenous waste that is ammonia to urea. The reaction of this cycle is:

NH${}_3$ + CO${}_2$ + aspartate + 3 ATP + 2 H${}_2$O → urea + fumarate + 2 ADP + 2 P${}_i$ + AMP + PP${}_i$

There is requirement of 3 molecules of ATP for the conversion of ammonia to urea.

Thus, the correct answer is option C.