Urea cycle function — What does the urea cycle convert in order to protect the body from nitrogen toxicity?

Introduction / Context:
Ammonia is neurotoxic at elevated concentrations. The liver converts ammonia into urea via the urea cycle, enabling safe transport in blood and excretion by the kidneys. This detoxification is central to nitrogen metabolism.

Given Data / Assumptions:

• Ammonia arises during amino acid deamination.
• Urea is water soluble and relatively non-toxic.
• Cycle occurs primarily in hepatocytes (mitochondria and cytosol).

Concept / Approach:
The urea cycle consumes free ammonia and the amino group of aspartate, plus CO2 (as bicarbonate), using ATP to form urea. This process prevents accumulation of ammonia and maintains nitrogen balance, especially during high-protein intake or fasting when amino acids are catabolized.

Step-by-Step Solution:

Verification / Alternative check:
Clinical hyperammonemia in urea cycle disorders demonstrates the detoxifying role of this pathway; treatment strategies aim to reduce ammonia.

Why Other Options Are Wrong:

• Ketoacids to amino acids describes transamination, not the urea cycle.
• Amino acids to ketoacids occurs in deamination, preceding urea synthesis.
• “None” is incorrect because the cycle clearly detoxifies ammonia.

Common Pitfalls:
Confusing carbon flow (fumarate production) with nitrogen disposal; the cycle’s purpose is nitrogen detoxification.

Final Answer:
Ammonia into a less toxic form