<prompt> Source of nitrogen in urea cycle is:Glutamate and aspaateGlutamate and NH3Arginine and aspaateNH3 and aspaate  <response>: The urea cycleornithine cycle is a cycle of biochemical reactions that produces urea from ammonia. In mammals, the urea cycle takes place only in the liver. Function: Organisms that cannot easily and quickly remove ammonia usually have to conve it to some other substance, like urea or uric acid, which are much less toxic. Reactions: The urea cycle consists of five reactions. The cycle conves two amino groups, one from NH4 and one from Aspaate, and a carbon atom from HCO3-, to relatively nontoxic excretion product, urea, at the cost of four high-energy phosphate bonds. Nitrogen donors in the urea cycle are ammonia and aspaate. 