Urea cycle (hepatic ornithine cycle) — identify the correct set of net products formed per complete turn of the cycle, including the nitrogenous end product and the nucleotide byproducts generated from ATP utilization.

Introduction / Context:
The urea (ornithine) cycle detoxifies ammonia by converting it to urea in hepatocytes. Beyond urea, this cycle produces additional metabolites and nucleotide byproducts due to ATP consumption. Knowing the full set of products is essential for biochemistry, clinical metabolism, and interpreting lab tests in hyperammonemia.

Given Data / Assumptions:

• The cycle incorporates 2 nitrogen atoms (one from free ammonia via carbamoyl phosphate and one from aspartate) into urea.
• Carbamoyl phosphate synthetase I and argininosuccinate synthetase use ATP.
• Fumarate emerges from cleavage of argininosuccinate and links to the TCA cycle.

Concept / Approach:
The energetic bookkeeping shows the cycle costs 3 ATP equivalents per turn: 2 ATP are hydrolyzed by CPS I, and 1 ATP is hydrolyzed to AMP + PPi by argininosuccinate synthetase. Tracking the nucleotide forms produced identifies AMP and ADP among the products.

Step-by-Step Solution:
Carbamoyl phosphate formation: NH3 + CO2 + 2 ATP → carbamoyl phosphate + 2 ADP + Pi.Argininosuccinate formation: citrulline + aspartate + ATP → argininosuccinate + AMP + PPi.Cleavage: argininosuccinate → arginine + fumarate (fumaric acid).Final split: arginine + H2O → urea + ornithine (ornithine recycled).

Verification / Alternative check:
Counting outputs per full turn yields urea + fumarate as carbon skeleton products, and nucleotide byproducts AMP (from the ATP → AMP step) plus two ADP (from CPS I). This matches the option containing urea, fumaric acid, AMP, and ADP.

Why Other Options Are Wrong:
Option a incorrectly lists ammonia and ATP as products; ammonia is consumed, not produced, and ATP is hydrolyzed. Option c wrongly shows aspartate and ammonia as products; both are inputs. Option e ignores fumarate and nucleotide byproducts.

Common Pitfalls:
Confusing ATP → AMP (which counts as two high-energy bonds) with ATP → ADP; forgetting fumarate’s appearance and its anaplerotic link to the TCA cycle.

Final Answer:
1 molecule of fumaric acid, 1 molecule of urea, 1 molecule of AMP, and 2 molecules of ADP.