Ch. 12

• Genetic material must:

  • Be able to store information to control both the development and metabolic activities of a cell
  • Be stable for accurate replication
  • Be able to undergo mutations for genetic variability required for evolution
• Griffith's transformation experiment (1920s):

  • Strain (S): virulent, mucus capsule
  • Strain (R): not virulent, no capsule
  • Injecting mice with heat-killed (S) resulted in survival
  • Injecting mice with heat-killed (S) and live (R) resulted in death
  • Conclusion: Substance from dead (S) strain passed to living (R) strain to change it to (S)
• Avery, MacLeod, and McCarty (1940s):

  • Enzymes degrading DNA prevented transformation
  • Transforming substance had a molecular weight great enough for genetic variability
• Hershey and Martha Chase (1950s):

  • Worked with bacteriophage
  • Discovered only P32 (DNA) inside the bacteria
• DNA structure:

  • Chargaff's Rules: A%=T% and G%=C%
  • Rosalind Franklin showed DNA is a helix with repeating portions
  • Watson and Crick's double helix structure with sugar/phosphate backbone and paired bases A-T and G-C
• DNA replication during S stage of Interphase:

  • Semi-conservative replication with old and new strands
  • Unwinding by topoisomerase and DNA helicase
  • Complementary base pairing with RNA primase and DNA polymerase
  • Joining by DNA ligase
  • Prokaryotic replication is circular and fast, eukaryotic replication has multiple sites and bubbles
• RNA types:

  • mRNA carries DNA code
  • tRNA carries amino acids
  • rRNA is the workbench for translation
• Genetic code:

  • Degenerate with redundancy
  • Unambiguous with start and stop signals
  • Universal with exceptions in some organisms
• Transcription in the nucleus:

  • RNA polymerase adds complementary RNA nucleotides
  • Promoter, elongation, and termination steps
  • Processing in eukaryotes with cap, tail, and removal of introns
• Translation in the cytoplasm:

  • tRNA transfers amino acids to mRNA
  • Ribosome structure and function with A, P, and E sites
  • Translation requires initiation, elongation, and termination steps
• Gene expression:

  • Occurs when the gene product, the protein, is operating
  • First few amino acids determine protein's destination