Question

An individual affected by phenylketonuria lacks an enzyme that converts the amino acid ______ into ______

• A. tyrosine, phenylalanine
• B. phenylalanine, tyrosine
• C. homogentisic acid, phenylalanine
• D. homogentisic acid, tyrosine

Answer 1

Answer: (B)

phenylalanine, tyrosine

Phenylketonuria is an inherited disorder that increases the levels of a substance called phenylalanine in the blood. Phenylalanine is a building block of proteins (an amino acid). Phenylketonuria is caused by a mutated gene for the enzyme phenylalanine hydroxylase (PAH), which converts the amino acid phenylalanine ("Phe") to other essential compounds in the body, in particular tyrosine.

So, the correct answer is 'phenylalanine, tyrosine'.