Question

THE GENETIC REVOLUTION PKU Phenylketonuria (PKU), the recessively inherited genetic disorder of amino acid metabolism, is regarded as the gold-standard genetic disorder. Its discovery in 1935 laid the foundation for human biochemical genetics. Knowledge about PKU encompasses almost every area and most of the technol- ogy of human genetics. The three-dimensional structure of the enzyme (phenylalanine hydroxylase, or PAH) responsible for the disorder is known, and its regulatory, catalytic, and bind- ing sites have been mapped. Additionally, the PAH gene has been cloned and its mutational sites identified. Biochemical and behavioral defects in PKU and the correlation between genotype and phenotype are well known, and the risks to fetuses carried by affected females are recognized. The disorder can be diag. nosed prenatally, a treatment that prevents mental retardation is available, and a newborn-screening program is used throughout the developed world to detect and treat affected individuals. An animal model with a matching biochemical phenotype has been developed and used to study changes in brain structure, gene expression, and metabolism in this disorder. PKU seems to be a straightforward disorder caused by a mutant allele encoding a defective enzyme, but the disorder has complexities still being revealed. In rare cases, the PAH gene

ANSWE THE FOLLOWING QUESTIONS BASED ON THE TEXT ABOVE:

1) The amino acid tyrosine is synthesized from phenylalanine. Does this make tyrosine an essential amino acid in indivduals with PKU?

2) In addition to phenylalanine, high levels of what other compound(s) might show up in the urine of those with PKU? Why?

Answer 1

Ansel- A deficient activity of PAH (Phenylalanine hydroxylase) enzyme, that converts essential amino acid phenylalanine (Phe) into tyrosine (Tyr), a non essential aminoacid that becomes essential in Pku (phenylketonuria), → Tyrosine becomes essential because it cannot be synthesized. Ans-2= Excretion of phenyl-keto compound, phenylpyruvic acid found in large amounts in weine. Dietary proteins Melanine Phenyl Pyruvad Dopamine ho & Phenylalanine i Tyrosinet Phenylketonuria proteins