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Phenylketonuria (PKU) is an autosomal recessive disorder in which an affected individual is unable to metabolise the amino acid phenylalanine - VCE - SSCE Biology - Question 3 - 2004 - Paper 1
Question 3
Phenylketonuria (PKU) is an autosomal recessive disorder in which an affected individual is unable to metabolise the amino acid phenylalanine. The defect is due to t... show full transcript
Worked Solution & Example Answer:Phenylketonuria (PKU) is an autosomal recessive disorder in which an affected individual is unable to metabolise the amino acid phenylalanine - VCE - SSCE Biology - Question 3 - 2004 - Paper 1
Step 1
a. Explain this observation.
Answer
In the metabolic pathway involving phenylalanine and tyrosine, when phenylalanine hydroxylase is deficient, phenylalanine accumulates in the body. This results in lower levels of tyrosine since phenylalanine is not metabolized into tyrosine, which is essential for pigment production in hair and skin.
As a consequence, individuals with PKU exhibit lighter hair and skin compared to their non-affected siblings. The lack of pigmentation occurs because tyrosine is a precursor to melanin, the pigment responsible for color. Therefore, with reduced tyrosine levels due to the absence of phenylalanine hydroxylase, there is insufficient melanin production, leading to lighter pigmentation.