MCB4403 Prokaryotic Biology FSU August 26, 2015

Prokaryotic Cells

  • lack true membrane nucleus

Eukaryotic Cells

  • Membrane enclosed nucleus
  • larger than prokaryotic cells
  • more complex morphologically

Microbes include 3 domains:

  • bacteria
  • archaea
  • eukarya

These 3 domains are based on a comparison of ribosomal RNA.

Domain Bacteria

  • single celled
  • cell wall with peptidoglycan
  • no membrane bound nucleus
  • cyanobacteria produce large amounts of oxygen

Domain Archaea

  • different from bacteria by rRNA (16S) gene
  • lack peptidoglycan in cell wall
  • unique membrane lipids
  • archaeal ribosomes similar to eukaryotic ribosomes
  • Live in extreme environments

Domain Eukarya

  • Protists
    • algae (photosynthetic)
    • protozoa (motile)
    • slime molds (2 life cycle stages)
    • water molds (devastating disease in plants)
  • Fungi
    • yeast (unicellular)
    • mold (multicellular)

What are some acellular infectious agents?

  • Viruses
    • smallest microbes
    • need host cell to replicate
    • can cause cancer
  • Viroids/Virusoids
    • infectious agents made of RNA (ex: HDV)
  • Prions
    • infectious proteins


  • DNA or RNA genome
  • Genome surrounded by protein coat (capsid) enclosed in lipid envelope
    • Nucleic acid → capsid →envelope
  • intracellular parasites

What is a Microbe?

Living creatures:

  • proteins, nucleic acids, lipids, sugars
  • metabolize, grow, reproduce, respond to environment

Microbes have the greatest diversity of genomes

Genomes: organism’s total genetic content

Metagenomics: study of genetic material recovered from environmental samples

Reconstruction of 1918 Flu Virus

  1. PCR
  2. Gene sequencing
  3. Gene reconstruction
  4. Reverse genetics, synthetic biology
  5. Experiment in tissue culture/animal models

Microbe Timeline

Mid 1600’s: Light microscope invented; Robert Hooke observes small eukaryotes

1676: van Leeuwenhoek discovers bacteria

1688: Redi shows flies do not spontaneously generate

1861: Louis Pasteur shows microbes do not grow in liquid unless introduced from outside

Louis Pasteur

  • Microbes cause fermentation
  • early vaccine development
  • pasteurization kills pathogen/microbes but ≠ sterilization

Germ Theory of Disease

  1. Germs can infect/grow on food
  2. Do germs cause disease?
  3. Are germs found in infected tissue?

Koch’s Postulates

  1. Microbe always present in diseased
  2. Microbe grown in pure culture
  3. Introduce pure microbe into healthy individual (individual becomes sick)
  4. Same microbe re-siolated from now-sick individual

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