Nerve activates contraction

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CHAPTER 27 PROKARYOTES AND THE ORIGINS OF
METABOLIC DIVERSITY
Bacillus anthracis spores in lung bronchiole
E. coli on surface of human skin
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Theyre (almost) everywhere!

• Prokaryotes were the earliest organisms on Earth
  and evolved alone for 1.5 billion years.

Vibrio cholerae - Gram-negative, facultatively
anaerobic, causes Asiatic cholera.
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Current taxonomy recognizes two prokaryotic
domains domain Bacteria and domain Archaea.

• Domain Archae (Archaebacteria)
• Lack peptidoglycan in c.w.
• More than one RNA poly-ase
• Histones assoc. with DNA.
• Introns in some genes

Halophilic bacterium
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Domain Archae

• Methanogens form CH4 from H2 and CO2 or
  acetate. Requires anaerobic conditions (bottom
  of pond, landfill, sewage digester)
• Halophiles require extremes in salt (gt 10),
  contain pigment (bacteriorhodopsin) that can
  absorb light and create H gradient.
• Thermoacidophiles found in geothermal springs
  (high heat) and low pHs.

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Alicyclobacillus spp. - an acidophilic,
thermophilic, spore forming bacterium
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Domain Bacteria (Eubacteria)

• Contain peptidoglycan in c.w.
• One type of RNA poly-ase.
• Lack introns in genome.
• Sensitive to antibiotics (streptomycin and
  chlroamphinicol)
• Ex. Purple bacteria, free-living, enteric,
  mycoplasmas, actinomycetes (soil bacteria),
  cyanobacteria, spirochetes, chlamydias.

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Structure and Morphology

• Most prokaryotes are unicellular some colonial
• In nearly all prokaryotes, a cell wall maintains
  the shape of the cell, affords physical
  protection, and prevents the cell from bursting
  in a hypotonic environment.
• The most common shapes among prokaryotes are
  spheres (cocci), rods (bacilli), and helices.

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Staphylococcus
Streptococcus
Diplococcus
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Nearly all prokaryotes have a cell wall external
to the plasma membrane

• Most bacterial cell walls contain peptidoglycan,
  a polymer of modified sugars cross-linked by
  short polypeptides.
• The walls of archaea lack peptidoglycan.
• Chemistry of cell wall allows for identification
  and classification. Gram staining.

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• Gram-positive bacteria have simpler cell walls,
  with large amounts of peptidoglycans and only one
  membrane. Stains purple.

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• Gram-negative bacteria have more complex cell
  walls and less peptidoglycan. Have a double
  lipopolysaccharide membrane. Stains Pink.
• An outer membrane on the cell wall contains
  lipopolysaccharides, carbohydrates bonded to
  lipids.

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• Among pathogenic bacteria, gram-negative species
  are generally more threatening than gram-positive
  species.
• The lipopolysaccharides on the walls are often
  toxic and the outer membrane protects the
  pathogens from the defenses of their hosts.
• Gram-negative bacteria are commonly more
  resistant than gram-positive species to
  antibiotics because the outer membrane impedes
  entry of antibiotics.

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• Many prokaryotes secrete another sticky
  protective layer, the capsule, outside the cell
  wall.
• Composed of protein or polysaccharides.
• Capsules adhere the cells to their substratum.
• They may increase resistance to host defenses.
• They glue together the cells of those prokaryotes
  that live as colonies.
• i.e. R and S strains of Griffith experiment.

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• Another way for prokaryotes to adhere to one
  another or to the substratum is by surface
  appendages called pili (or fimbriae).
• Pili/fimbriae can fasten pathogenic bacteria to
  the mucous membranes of its host.
• Formed from protein? Pilin
• Sex Pili

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Many prokaryotes are motile

• About half of all prokaryotes are capable of
  directional movement.
• The action of flagella, scattered over the entire
  surface or concentrated at one or both ends, is
  the most common method of movement.
• The flagella of prokaryotes differ in structure
  and function from those of eukaryotes.

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• In a prokaryotic flagellum, chains of a globular
  protein wound in a tight spiral from a filament
  which is attached to another protein (the hook),
  and the basal apparatus.
• Rotation of the filament is driven by the
  diffusion of protons into the cell through the
  basal apparatus after the protons have been
  actively transported by proton pumps in the
  plasma membrane.

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• A second motility mechanism is found in
  spirochetes, helical bacteria.
• Two or more helical filaments under
  (internalized) the cell wall are attached to a
  basal motor attached to the cell.
• When the filaments rotate, the cell moves like a
  corkscrew. Useful in thick fluids.
• A third mechanism occurs in cells that secrete a
  jet of slimy threads that anchors the cells to
  the substratum.
• The cell glides along at the growing end of
  threads.

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• In a relatively uniform environment, a
  flagellated cell may wander randomly.
• In a heterogenous environment, many prokaryotes
  are capable of taxis, movement toward or away
  from a stimulus.
• With chemotaxis, binding between receptor cells
  on the surface and specific substances results in
  movement toward the source (positive chemotaxis)
  or away (negative chemotaxis).
• Other prokaryotes can detect the presence of
  light (phototaxis) or magnetic fields
  (magnetotaxis).

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Growth, reproduction and genetic exchange
Endospore

• Binary fission Conjugation Transduction
  Transformation
• Endospore formation. Resting structures that
  withstand high heat, radiation, desiccation,
  toxins. Allow survival for hundreds of years.
  Form during unfavorable conditions. Low in water
  content (15 vs. 90 of normal cell). Tough wall
  forms that is one of the toughest biological
  structures.

Clostridium botulinum - Causes botulism.
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Metabolic Diversity

• Nutritional modes depend on how an organism
  obtains energy and a carbon source from the
  environment to build the organic molecules of
  cells.

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• Photoautotrophs are photosynthetic organisms that
  harness light energy to drive the synthesis of
  organic compounds from carbon dioxide.
• Among the photoautotrophic prokaryotes are the
  cyanobacteria.
• Among the photosynthetic eukaryotes are plants
  and algae.

Cyanobacteria
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• Chemoautotrophs need only CO2 as a carbon source,
  but they obtain energy by oxidizing inorganic
  substances, rather than light.
• These substances include hydrogen sulfide (H2S),
  ammonia (NH3), and ferrous ions (Fe2) among
  others. Use these to form H gradient then ATP.
• This nutritional mode is unique to prokaryotes.
• Symbionts with tubeworms at hydrothermal vents

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• Photoheterotrophs use light to generate ATP but
  obtain their carbon in organic form.
• This mode is restricted to prokaryotes.
• Chemoheterotrophs must consume organic molecules
  for both energy and carbon.
• This nutritional mode is found widely in
  prokaryotes, protists, fungi, animals, and even
  some parasitic plants.

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The majority of known prokaryotes are
chemoheterotrophs.

• These include saprobes, decomposers that absorb
  nutrients from dead organisms, and parasites,
  which absorb nutrients from the body fluids of
  living hosts.
• Some of these organisms (such as Lactobacillus)
  have very exacting nutritional requirements,
  while others (E. coli) are less specific in their
  requirements.

Lactobacillus sp.
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• Prokaryotes are responsible for the key steps in
  the cycling of nitrogen through ecosystems.
• Some chemoautotrophic bacteria convert ammonium
  (NH4) to nitrite (NO2-).
• Others denitrify nitrite or nitrate (NO3-) to
  N2, returning N2 gas to the atmosphere.
• A diverse group of prokaryotes, including
  cyanobacteria, can use atmospheric N2 directly.
• During nitrogen fixation, they convert N2 to
  NH4, making atmospheric nitrogen available to
  other organisms for incorporation into organic
  molecules.

Nitrosomonas spp
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• Nitrogen fixing cyanobacteria are the most
  self-sufficient of all organisms.
• They require only light energy, CO2, N2, water
  and some minerals to grow.

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• The presence of oxygen has a positive impact on
  the growth of some prokaryotes and a negative
  impact on the growth of others.
• Obligate aerobes require O2 for cellular
  respiration.
• Facultative anerobes will use O2 if present but
  can also grow by fermentation in an anaerobic
  environment.
• Obligate anaerobes are poisoned by O2 and use
  either fermentation or anaerobic respiration.
• In anaerobic respiration, inorganic molecules
  other than O2 accept electrons from electron
  transport chains.

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• Gram-negative, facultatively anaerobic, rod.
• Transmitted by the rat flea to humans, it caused
  the bubonic plague.

Yersinia pestis

• Gram-negative, tiny flagella at the end of the
  cell.
• main cause of chronic superficial gastritis,
  associated with both gastric and duodenal ulcers
• lives in the interface between the surface of
  gastric epithelial cells (the lining of the
  stomach).

Helicobacter pylori