Final answer:
The urea cycle converts ammonia to urea through five intermediate steps. The first two steps occur in the mitochondria and the last three occur in the cytosol. Ornithine transcarbamylase is a key enzyme in this process.
Step-by-step explanation:
The urea cycle is the mechanism of conversion of ammonia to urea involving five intermediate steps. Of these five steps, the first two occur in the mitochondria and the last three in the cytosol. The urea cycle uses five different enzymes, with ornithine transcarbamylase playing a key role. Urea concentration in the blood, called blood urea nitrogen (BUN), is used to monitor kidney function.