Question

What happens if there is a defect in only one of the four enzymatic steps of the urea cycle?

a) The defect will not result in any change until multiple enzymes in the urea cycle are affected.

b) The defect will not result in any change unless carbamoyl phosphate synthetase is also affected.

c) The defect results in hyperammonemia, which is an elevated blood NH4+ level.

d) The defect results in hypoammonemia, which is a decreased blood NH4+ level.

Answer 1

C is the correct answer.

waste nitrogen is derived from amino acid breakdown. In urea cycle, ammonia fixed with CO₂ in to urea by liver. When urea cycle does not function normally , it can't fix into urea with CO₂ than ammonia level will increase in blood caused hyperammonemia. So the rest options are incorrect because only defect occur in first four step out of five which catalyzed by carbamoyl phosphate synthase, ornithine transcarbomylase, arginosuccinate synthase and arginosuccinate lyase.