In which part of the cell does the first step of the urea cycle occur?

The first step of the urea cycle occurs in the mitochondria of the cell. In this initial phase, ammonia, which is a toxic byproduct of amino acid catabolism, is combined with carbon dioxide to form carbamoyl phosphate. This reaction is catalyzed by the enzyme carbamoyl phosphate synthetase I. The mitochondrial location is crucial because it allows for the immediate processing of ammonia, ensuring that it does not accumulate to harmful levels within the cytoplasm.

Furthermore, the urea cycle is designed to detoxify ammonia, and since mitochondria are involved in energy metabolism and have a crucial role in ammonium ion regulation, the presence of this cycle in the mitochondria aligns with the cell's need to efficiently manage nitrogen waste. Understanding this function reflects the broader context of metabolic pathways and their compartmentalization within cellular structures.