CH 461 Lecture Notes - Lecture 19: Essential Amino Acid, Urea Cycle, Citric Acid Cycle
Document Summary
In humans, excess amino groups are detoxified by conversion to urea. Ammonia in high concentrations is toxic to all organisms. For example, humans with kidney failure die because the level of ammonia increases in the bloodstream. Organisms that live in water, including fish and microorganisms, simply eliminate ammonia directly and allow it to be diluted by their environment. Terrestrial organisms, on the other hand, convert the ammonium groups to other compounds that are less toxic. Birds and reptiles synthesize uric acid as the primary nitrogen excretion compound. The white crystals of uric acid constitute the unsightly part of bird droppings; the poor solubility of uric acid makes the results hard to remove from a car or a statue in a park, for example. Mammals synthesize urea, ultimately from carbonate and ammonium ions. In mammals, muscle breakdown or excess protein intake results in an imbalance between the fates of the carbon chains and the amino nitrogen.
