Genes and Proteins

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Genes and Proteins

• Another defective enzyme in the same pathway,
  phenylalanine hydroxylase (PAH), leads to
  phenylalanine accumulation which causes the
  condition known as phenylketonuria (PKU)
• http//www.youtube.com/watch?vKUJVujhHxPQ
• http//www.youtube.com/watch?v4xkH8_-lkFIf
  eaturerelated
• http//www.youtube.com/watch?vhpaki7F4HR0f
  eaturerelated
• Incidence of PKU, characterized by severe mental
  retardation, is about one in 8000 among Caucasian
  births.
• A defective enzyme results from a mutant gene

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Figure 1.9 Metabolic pathway for the breakdown
of phenylalanine and tyrosine
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Figure 1.10 Inborn errors of metabolism in the
breakdown of phenylalanine and tyrosine
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Genes and Proteins

• In the 1940s George W. Beadle and Edward L.
  Tatum, using a filamentous fungus Neurospora
  crassa, demonstrated that each enzyme is encoded
  in a different gene.
• Their experimental approach, now called genetic
  analysis, led to the one geneone enzyme
  hypothesis.

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Figure 1.11 Beadle and Tatum obtained mutants of
the fi lamentous fungus Neurospora crassa
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Genes and Proteins
Figure 1.12A Mutant spores can grow in complete
medium but not in minimal medium
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Figure 1.12B Each new mutant is tested
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Figure 1.12C Mutants that can grow on minimal
medium supplemented with amino acid are tested
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Figure 1.12D Mutants unable to grow in the
absence of arginine are tested with likely
precursors of arginine
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Figure 1.13 Metabolic pathway for arginine
biosynthesis inferred from genetic analysis of
Neurospora mutants
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