Prokaryotes

• Every living organism is composed of either Prokaryotic or Eukaryotic cells
• Tree of life

  • Bacteria
  • Eukaryotes
  • Archaea
• Prokaryotic cells developed 3.5 billion years ago
• Prokaryotic cells are the most abundant type on earth today
• Collective biomass of prokaryotic cells on the world is 10 times that of eukaryotes
• Prokaryotic cells are simple in structure but biochemically diverse
• Prokaryotic cells do not have a membrane bound nucleus
• Eukaryotic cells developed from prokaryotic cells around 2 billion years ago (maybe earlier) and have a membrane bound nucleus
• Prokaryotes can be divided into two domains

  • Bacteria
  • Archaea
• Archaea often live in very extreme environments
• Bacteria have enormous medical and economic importance
• If life is ever found on another planet it will probably be similar to Archaea as extremophiles can colonise extreme environments on Earth
• Components of a prokaryotic cell

  • Nucleoid region: contains circular DNA, no nuclear membrane
  • Plasma membrane: has the same basic structure of all biological membranes
  • Some prokaryotes have infoldings of the plasma membrane which contain specialized enzymes
  • The cytoplasm contains ribosomes and little else
  • Many prokaryotes have a cell wall
  • Some prokaryotes have flagella composed of the protein Flagellin
  • Pili are composed of the protein Pilin and help bacterial stick to their substrate or to each other
  • Many bacteria also secret a Capsule usually of polysaccharides
• Bacteria have a diverse range of shapes the most common being Cocci (spherical),bacilli (rod shaped), and spirochetes (helical)
• Chromosome


  Circular DNA in prokaryotic cells
• Plasmids


  Small circular DNA molecules in prokaryotic cells
• Thylakoid membranes in cyanobacteria
• Prokaryotic flagella have a hook, motor, filament and rod
• Prokaryotic flagella are used for movement and sensitivity
• Prokaryotic cells can undergo conjugation to transfer genetic material
• Shapes of bacteria

  • Spherical (cocci)
  • Rod-shaped (bacilli)
  • Spiral (spirochetes)
• Bacterial cell wall

  • Protects the cell against mechanical and osmotic shocks
  • Composed of the molecule peptidoglycan
• Types of bacterial cell walls

  • Gram positive (thick, single layer)
  • Gram negative (thin, double layer)
• Gram-positive bacteria are susceptible to antibiotic resistance, gram-negative are resistant
• Pathogenic bacteria

  • Chlamydia trachomatis (cause of infectious blindness)
  • Vibrio cholerae (causes cholera)
  • Yersinia pestis (causes plague)
  • Clostridium tetani (causes tetanus)
  • Clostridium botulinum (causes botulism)
  • Streptococcus pneumoniae (causes pneumonia)
• Uses of bacteria in biotechnology

  • Medical (produce proteins, diagnostics)
  • Agricultural (genetic modification of plants)
  • Environmental (bioremediation)
  • Industrial (food production, wine storage)
• Types of prokaryotic nutrition

  • Photoautotrophs (use light to synthesize organic compounds)
  • Chemoautotrophs (use inorganic substances for energy)
  • Photoheterotrophs (use light for ATP but organic carbon)
  • Chemoheterotrophs (use organic molecules for carbon and energy)
• Viruses

  Cannot self-repair, no energy transduction system, only visible with electron microscope
• Types of viral structure

  • Filamentous (nucleic acid in helix with protein subunits)
  • Spheroid (nucleic acid condensed in protein envelope)
  • Tailed spheroid (spheroid with tail)
  • Enveloped (have lipid envelope)
• SARS-CoV-2 is an enveloped single-stranded RNA coronavirus
• Comparisons of the three domains

  A) absent

  B) absent

  C) present

  D) absent

  E) absent

  F) present

  G) present

  H) absent

  I) absent

  J) unbranched hydrocarbons

  K) some branched hydrocarbons

  L) unbranched hydrocarbons

  M) one kind

  N) several kinds

  O) several kinds

  P) formyl-methionine

  Q) methionine

  R) methionine

  S) very rare

  T) present in some genes

  U) present in many genes

  V) growth inhibited

  W) growth not inhibited

  X) growth not inhibited

  Y) absent

  Z) present in some species

  [) present

  \) present

  ]) present

  ^) absent

  _) no

  `) some species

  a) no

  
• Gram positive

  • Thick peptidoglycan cell wall (20-80nm)
  • simple, single layer cell wall
  • Teichoic acids
  • stains purple
• Gram negative:

  • Thin peptidoglycan cell wall
  • complex, double layer cell wall
  • lipopolysaccharides
  • stains pink
• Mode of nutrition among prokaryotes

  1. photoautotrophs
  2. chemoautotrophs
  3. photoheterotrophs
  4. chemoheterotrophs
• Photoautotroph: Photosynthetic organisms that use light energy to make their own organic compounds from CO2
• Chemoautotrophs: Use carbon dioxide as a carbon sources and obtain their energy by oxidizing inorganic substances
• Photoheterotrophs: use light to generate ATP but must obtain their carbon in an organic form
• Chemoheterotrophs: use organic molecules to supply both carbon and energy
• Types of virus:

  • Filamentous
  • spheroid
  • tailed spheroid
  • enveloped
• Filamentous virus: The nucleic acid is arranged in a helix, with the protein sub-units surrounded and stabilizing it e.g tobacco mosaic virus