Final answer:
Mutations in the PAH enzyme result in a defective shape that prevents it from catalyzing the conversion of phenylalanine to tyrosine, leading to phenylketonuria (PKU) and the accumulation of toxic levels of phenylalanine which can cause neurological damage.
Step-by-step explanation:
A mutation in the phenylalanine hydroxylase (PAH) enzyme causes the enzyme to stop functioning due to a change in the enzyme's structure. Enzymes are highly specific biological catalysts, and their activity is dependent on their three-dimensional structure, which is determined by their amino acid sequence. A mutation can alter an amino acid in a crucial part of the enzyme, leading to a defect in its shape. This structural change can affect the enzyme's ability to catalyze the conversion of phenylalanine to tyrosine, resulting in the accumulation of phenylalanine to toxic levels in the body, a condition known as phenylketonuria (PKU).
Without functional PAH, the elevated levels of phenylalanine can cause severe damage to the central nervous system and brain. Symptoms of PKU include delayed neurological development, hyperactivity, intellectual disability, and other severe health issues. It's vital for individuals with PKU to adhere to a phenylalanine-restricted diet to prevent these symptoms, and in countries like the United States and Canada, newborns are routinely tested for PKU to ensure early intervention.