BIO LEC 6 - Gene Functions

• • 1902 Archibald Garrod
  • 1st evidence of relationship between genes and enzyme
  • 1942 George Beadle and Edward Tatum
  • one gene-one enzyme hypothesis
  • gene > protein (gene products) > not all proteins are enzymes
  • enzyme - catalyze metabolic reactions
• Archibald Garrod in 1902

  • 1st relationship between genes and enzymes
  • studied Inborn Errors of Metabolism
  • Alkaptonuria
  • Phenylalanine > phenylalanine hydroxylase
  • Tyrosine
  • P hydroxypyruvate
  • Homogentisic Acid (HA) > HA oxidase
  • no HA oxidase > accumulation of HA > alkapton = oxidized HA
  • Maleylacetoacetic Acid
  • H2O + CO2
  • Phenylketonuria
  • Phenylalanine > phenylalanine hydroxylase
  • no phenylalanine hydroxylase > no tyrosine
  • Albinism
  • Phenylalanine > phenylalanine hydroxylase
  • Tyrosine > tyrosinase
  • 3,4 dihydroxy phenylalanine > tyrosinase
  • Melanin
• One Gene - One Enzyme

  • George Beadle - Edward Tatum in 1942
  • gene is reponsible for one enzyme - catalyzes metabolic reactions

  One Gene - One Protein

  • proteins are gene products
  • not all proteins are enzymes

  One Gene - One Polypeptide

  • hemoglobin = 2 alpha + 2 beta
  • antibody = 2 heavy chains + 2 light chains
• • George Gamow
  • genetic coding system
  • Marianne Manago and Severo Ochoa
  • synthetic RNAs using polynucleotide phosphorylase wherein + of UTP yields poly U
  • Nirenberg and Matthaei
  • artificial mRNAs and cell free system
  • controlling amounts of U and G predicts the amount of codons in random polymer
  • Har Khorana
  • synthetic mRNAs
  • dinucleotide, trinucleotide, tetranucleotide
  • Nobel Prize in 1968 with Nirenberg and Holley
• Nature and Characteristics of Genetic Code (Francis Crick and students)

  1. Unambiguous (rarely do you see a single codon coding for multiple amino acids)
  2. Universal (all share the same genetic code)
  3. Non-overlapping
  4. Continuous
  5. Triplet Code
  6. Degenerate (multiple codons code for the same amino acid)
  7. Stop (UGA, UAA, UAG) and Start (AUA - met; GUG - val) Signals
  8. Wobble Hypothesis in anticodon (precise pairing for the 1st and 2nd bases in the anticodon)