Urea cycle

The Urea Cycle is a cycle of biochemical reactions occuring in many animal organisms that produces urea from ammonia.

Urea is much less toxic than ammonia, therefore organisms which can't easily and quickly remove ammonia usually have to convert it to some other substance, like urea or uric acid.

Reactions of cycle:

• citruline? + NH₃ -> arginine? + H₂O
• arginine? + H₂O -> ornithine? + urea (catalyzed by arginase?)
• ornithine? + NH₃ + CO₂ -> citruline? + H₂O (catalyzed by [ornithine transcarbamoylase]?)

Summary reaction:

• 2 NH₃ + CO₂ -> urea + H₂O