Question

Urea is formed in liver from

• A. Ammonia and nitrogen
• B. Ammonia and carbon dioxide
• C. Ammonia, carbon dioxide and aspartic acid
• D. Ammonia and carbon monoxide

Answer 1

The correct option is C Ammonia, carbon dioxide and aspartic acid

The urea cycle or the ornithine cycle describes the conversion reactions of ammonia into urea. In urea cycle, one amine group comes from oxidative deamination of glutamic acid while the other amine group comes from aspartic acid. Aspartic acid is regenerated from fumaric acid produced by the urea cycle. The fumaric acid first undergoes reactions through a portion of the citric acid cycle to produce oxaloacetic acid, which is then changed by transamination into aspartic acid.