When it comes to the phases of the urea cycle, we're going to say the urea cycle takes place in two phases. Phase A is our preparation phase, and Phase B is our conversion phase. In the preparation phase, we convert our Ammonium ions into Carbamoyl Phosphate. This consumes ATP and uses Carbon Dioxide found within the mitochondrial matrix. In the conversion step, it produces urea from the Carbamoyl Phosphate as well as from the Aspartate molecule. This phase also consumes ATP. If we take a look here, we have our ammonium ion, and we're going to have the injection of Carbon Dioxide again from the mitochondrial matrix as well as the consumption of ATP. This will help create the carbonyl phosphate group. This represents our urea cycle.
Here we're crossing the mitochondrial matrix with this orange line. We're going to say that in Phase B, we are producing urea, which remember is a carbonyl, with two NH2 groups attached. This happens because of the Carbonyl Phosphate as well as Aspartate. And again, remember in Phase B, we also have the consumption of another ATP molecule. This is an energy-demanding pathway; we require the use of ATP in order to complete both phases of the urea cycle.