Urea Cycle Quiz: Test Your Knowledge of Nitrogen Metabolism

Which amino acid is nutritionally non-essential for the human organism?

Which amino acid is nutritionally essential for the human organism?

Select the enzyme that can directly catalyze the release of ammonia.

Select the enzyme that can incorporate free ammonia into organic compounds.

Which statement is false?

Which of the following participates in the urea cycle?

Which molecule is involved in the activation of the urea cycle?

Which substance is NOT involved in the production of urea from NH4+ via the urea cycle?

Where are the enzymes of the urea cycle located?

A nitrogen atom of which compound is incorporated in the urea by an enzyme of the urea cycle?

Which process in the urea cycle requires the hydrolysis of ATP?

Conversion of ornithine to citrulline is a step in the synthesis of:

How much energy, in terms of high-energy bonds, is consumed in the synthesis of one urea molecule?

In the urea cycle, ornithine transcarbamoylase catalyzes:

Which enzyme is involved in the synthesis of proline?

The amino acids serine, alanine, and cysteine can be catabolized to yield:

Urea Cycle

Ornithine transcarbamoylase catalyzes the formation of citrulline from ornithine and another reactant.
The reaction is similar to transamination in that it involves the coenzyme pyridoxal phosphate (PLP).
ATP hydrolysis is not required for the urea cycle.

Amino Acid Metabolism

Serine, alanine, and cysteine can be catabolized to yield pyruvate.
Serine or cysteine may enter the citric acid cycle as acetyl-CoA after conversion to pyruvate.
Tyrosine requires dietary phenylalanine, phenylalanine hydroxylase, tetrahydrobiopterin, and dihydrobiopteridine reductase for its synthesis.
Proline involves glutamate, glutamic semialdehyde, and pyrroline-5-carboxylate reductase in its synthesis.
Tryptophan can be the precursor of nicotinamide, alanine, and serotonin.

Nutritionally Essential and Non-Essential Amino Acids

Nutritionally non-essential amino acids for the human organism include proline, cysteine, and tyrosine.
Nutritionally essential amino acids for the human organism include isoleucine, phenylalanine, and tryptophan.

Enzymes and Ammonia

Glutaminase, glutamate dehydrogenase, and arginase can directly catalyze the release of ammonia.
Glutamine synthetase, glutamate dehydrogenase, mitochondrial carbamoylphosphate synthetase, and asparagine synthetase can incorporate free ammonia into organic compounds.
Aspartate is a nitrogen donor in the course of urea formation, and one of the nitrogen atoms of urea is derived from free ammonia.

Test your knowledge on the urea cycle and nitrogen metabolism with this quiz. Identify substances involved in urea production and understand the incorporation of nitrogen atoms in the cycle. Select the correct answers to questions related to NH4+ conversion to urea and nitrogen compound incorporation.