Genes and Proteins

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Genes and Proteins
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Gene Concept
Molecular Genetics
Watson Crick
Classical Genetics
Gene Concept
20th Century
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Garrod, 1902Inborn errors of metabolismOne
Gene - One Metabolic Block
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Beadle Ephrussi, 1935transplant experiments
with imaginal disks
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Beadle Ephrussi, 1935Interpretations
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Beadle Ephrussi, 1935Interpretations
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Beadle and Tatum, 1941
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Creating Mutants
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Screening for Auxotrophs
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Pathways
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Example 1
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Example 2
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One Gene - One Polypeptide
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A Diagnostic Test for AllelesComplementation
Test, Lewis 1942
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Three mutations two allelic and one non-allelic
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Allelic mutations dont complement each other
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Non-allelic mutations do complement each other
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Structure of Genes

• Pre-1940s concept
• Beads on a string
• Gene
• unit of function
• unit of structure, indivisible by mutation or
  recombination

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Oliver, 1940

• Recombination within the lozenge gene
• Used two mutations at this gene
• spectacle lzs
• glassy lzg
• These two alleles should not recombine according
  to beads-on-a-string hypothesis

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Oliver, 1940

• However, the cross lzg / lzs x lzg / lzs
  produced 0.2 wild types
• Moreover, bordering markers seemed to indicate
  that recombination had occured

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• However, the cross lzg / lzs x lzg / lzs
  produced 0.2 wild types
• Moreover, bordering markers seemed to indicate
  that recombination had occured

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Intragenic recombination in viruses
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Benzer 1955
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A map of recombination sites within the rII gene
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Benzer

• Numerous recombination sites within genes
• Comparison of recombination and physical maps
  indicated 1 site per 2.3 nucleotides
• almost molecular resolution
• Refuted beads on a string hypothesis.
• Cistrons code for proteins

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Yanofsky, 1965mutations and amino acid
substitutions are colinear

• Bacteria
• Used genetic recombination analyses amino acid
  sequencing

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Molecular Definition of a Gene

• The entire nucleotide sequence that is required
  for the synthesis of a functional polypeptide or
  RNA molecule

a simple monocistronic prokaryotic gene
control region
coding region
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prokaryotic operons
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eukaryotic simple genes
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eukaryotic complex genes
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A small genome
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Central Dogma of Biology
Genetic Code
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Coding Ratios Triplet Code?
coding ratio 1 2 3 R
number of words 41 4 42 16 43 64 4R
adequacy 4 lt 20 16 lt 20 64 gt 20
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Confirmation that the genetic code is a triplet
code frame shift suppressors
THE BIG CAT ATE THE FAT RAT
wild type
THE BIG CAT ATE THE FAT RAT
1 deletion
THE BGC ATA TET HEF ATR AT...
large frame shift mutation
THE BIG CAT ATE THE FAT RAT
2 nucleotides deleted
THE BCA TAT ETH EFA TRA T...
large frame shift mutation
THE BIG CAT ATE THE FAT RAT
3 nucleotides deleted
THE BAT ATE THE FAT RAT...
small frame shift mutation
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Early investigations of the genetic code using in
vitro translation systemsusing uniform
precursor pools to produce artificial mRNA
in vitro translation system
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Early investigations of the genetic code using
in vitro translation systems
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final investigations of the genetic code using in
vitro translation systemsmaking specific
3-nucleotide mRNAs
for each codon
in vitro translation system
check which aa associates with ribosome
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The Genetic Code is Degenerate
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A more typical display of the genetic code
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Central Dogma of Biology
Genetic Code
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DNA cannot code for protein synthesis directly
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RNA Intermediate in protein synthesis

• Volkin and Astrachan, 1956
• Viral infection of bacteria
• Burst of RNA synthesis
• RNA short-lived
• RNA similar to sequences of virus, not bacterial
  host

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RNA Intermediate hybridizes with viral DNA
Spiegelman et al., 1961
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Results

• Results

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Specialist or Generalist Ribosomes?
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Central Dogma of Biology
Genetic Code