A. Glutamate and aspartate
B. Glutamate and NH3
C. Arginine and aspartate
D. NH3 and aspartate
Ans. ‘D’ NH3 and aspartate
The urea cycle/ornithine cycle is a cycle of biochemical reactions that produces urea from ammonia. In mammals, the urea cycle takes place only in the liver.
Organisms that cannot easily and quickly remove ammonia usually have to convert 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 converts two amino groups, one from NH4+ and one from Aspartate, 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 aspartate.