Phenylketonuria (PKU) is an example of a genetic disorder which affects the following metabolic pathway - Scottish Highers Human Biology - Question 2 - 2017
Question 2
Phenylketonuria (PKU) is an example of a genetic disorder which affects the following metabolic pathway.
dietary protein
⇣
amino acid phenylalanine
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Worked Solution & Example Answer:Phenylketonuria (PKU) is an example of a genetic disorder which affects the following metabolic pathway - Scottish Highers Human Biology - Question 2 - 2017
Step 1
Describe how a substitution mutation would alter the gene coding for enzyme 1.
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Answer
A substitution mutation replaces one nucleotide in the DNA sequence with another. This change may result in a different amino acid being produced, affecting the structure and function of enzyme 1.
Step 2
Explain how a substitution mutation may cause the synthesis of a faulty enzyme.
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Answer
The mutation can alter the sequence of amino acids in the enzyme. If the substitution introduces a premature stop codon or disrupts the active site, the enzyme may not function properly, leading to its malfunctioning.
Step 3
why PKU results in a build-up of phenylalanine;
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PKU leads to a build-up of phenylalanine because enzyme 1 is faulty and cannot convert phenylalanine into tyrosine, which prevents the breakdown of phenylalanine.
Step 4
why individuals with PKU can still produce melanin.
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Individuals with PKU can still produce melanin because tyrosine, which is produced by enzyme 2, can still enter the metabolic pathway to form melanin, albeit at reduced levels.
Step 5
State the term used to describe this type of diagnostic testing.
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The term used to describe this type of testing is 'post-natal screening'.
Step 6
Describe how brain damage can be prevented in babies diagnosed with PKU.
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Brain damage can be prevented by implementing a restricted diet low in phenylalanine immediately after diagnosis, ensuring that phenylalanine levels do not rise to toxic levels.
Step 7
Calculate the percentage chance of their next child having this disorder.
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Since both parents are carriers of the autosomal recessive allele for PKU, there is a 25% chance that their next child will inherit the disorder. This can be calculated using a Punnett square, which shows the genetic combinations of the alleles.
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