Which amino acid(s) are metabolites in the urea cycle, but are not used as building blocks of proteins? a) ornithine b) citrilline c) glutamate d) a and b e) a, b, and c

D)

Explanation:

Ornithine and Citrulline are the amino acids which are metabolites in the urea cycle but not used as building blocks of proteins.

Ornithine is the most important reactant in urea cycle that is responsible for 80% of the excretion of nitrogen in the body. It even improves liver function.

Even Citrulline is not used in the building blocks of protein, Citrulline is mainly used to widen blood vessels and may play a role in muscle building.