Transcription

• How DNA codes proteins:

  A message must be present because in higher organisms, proteins are assembled in the cytoplasm, but DNA remains in the nucleus
• Central Dogma: DNA -> RNA -> protein
• DNA is made of 4 nucleotides one after the other
• Eukaryotes:

  • have a nucleus with a nuclear membrane
  • organelles present
  • linear chromosomes
  • DNA wraps around balls of histone proteins
  • mitosis and meiosis
  • higher organisms
• Prokaryotes:

  • no enclosed nucleus
  • no enclosed organelles
  • circular chromosome
  • "naked" DNA
  • divide by fission; replicated DNA passes to each daughter cell
  • bacteria and algae
• Transcription uses DNA as a template to make RNA
• DNA-dependent RNA polymerases must know where to start making mRNA: that built in information is called a promoter
• Prokaryotic promoters are the same for making all types of RNA: mRNA, rRNA, and tRNA
• Eukaryotes have 3 different RNA polymerases and promoters:

  • Pol I for large RNAs like rRNA
  • Pol II for mRNA
  • Pol III for small RNAs like tRNA
• Bacterial promoters are the same for any mRNA strand that needs to be made