Carbamoyl group of carbamoyl phosphate is derived from ?
Ammonia
Citrulline
Ornithine
Arginosuccinate
Ans. is 'a' i.e., Ammonia 1st reaction of urea cycle is synthesis of carbamoyl phosphate by condensation of ammonia (NH4') and CO2.The carbamoyl group of carbomoyl phosphate is derived from NH4. and a bicarbonate ion.The reaction is energetically demanding (two ATP) and is catalyzed by carbomoyl phosphate synthase LCPS-I is allosterically activated by N-acetyl glutamate.