Bacteria and Archaea

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Bacteria and Archaea

• Chapter 27

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YOU MUST KNOW

• The key ways in which prokaryotes differ from
  eukaryotes with respect to
• Genome
• Membrane bound organelles
• Size
• Reproduction
• Mechanisms that contribute to genetic diversity
  in prokaryotes, including
• Transformation
• Conjugation
• Transduction
• Mutation

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Structural Functional Adaptations

• Structural and functional adaptations contribute
  to prokaryotic success
• Both the domain Bacteria and the domain Archaea
  are made up of prokaryotes.
• Prokaryotes have NO TRUE NUCLEI or internal
  compartmentalization.
• The DNA of prokaryotes is concentrated in the
  nucleoid region and has little associated
  protein.
• Relative to eukaryotes, prokaryotes have simple,
  small genomes.
• In addition to their one major chromosome,
  prokaryotic cells may also possess smaller,
  circular, independent pieces of DNA called
  plasmids.

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Prokaryotic Shapes

• In general, prokaryotes exist in three common
  shapes
• Cocci (round)
• Bacillus (rod-shaped)
• Spirilla (spiral)

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Prokaryotic Reproduction

• Prokaryotes reproduce through an asexual process
  called binary fission, and they continually
  synthesize DNA.

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Prokaryotic Structure

• Outside their cell membranes, most prokaryotes
  possess a cell wall that contains peptidoglycan.
• Gram-positive bacteria have simpler cell walls
  with more peptidoglycan.
• Gram-negative bacteria have cell walls that are
  structurally more complex.

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Prokaryotic Structure

• The cell wall of many prokaryotes is covered by a
  capsule, a sticky layer of polysaccharide or
  protein.
• The capsule enables prokaryotes to adhere to
  other substrate or to other individuals in a
  colony. Some capsules protect against
  dehydration.
• Some prokaryotes stick to their substrate or to
  one another by means of hair-like appendages
  called fimbriae.
• The ability of some prokaryotes to withstand
  harsh conditions is attributed to endospores, a
  tough wall that forms outside the cell wall.

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Prokaryotic Motility

• Prokaryotes use appendages called pili that
  adhere to each other or to surrounding surfaces.
• About half of the prokaryotes are motile, because
  they possess whiplike flagella.

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Genetic Diversity in Prokaryotes

• Rapid reproduction, mutation, and genetic
  recombination promote genetic diversity in
  prokaryotes
• While mutation is the major source of genetic
  variation in prokaryotes, there are three
  mechanisms by which bacteria can transfer genetic
  material between each other
• Transformation (the uptake of foreign DNA from
  the surrounding environment).
• Conjugation (the direct transfer of genes from
  one prokaryote to another).
• Transduction (the transfer of genes from one
  prokaryote to another via a viral vector).

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Lateral Gene Transfer in Prokaryotes
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Major Nutritional Modes in Prokaryotes
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Oxygen Needs in Prokaryotes

• Obligate aerobes cannot growth without oxygen
  because they need oxygen for cellular
  respiration.
• Obligate anaerobes are poisoned by oxygen. Some
  use fermentation, whereas others extract chemical
  energy by another form of anaerobic respiration.
• Facultative anaerobes use oxygen if it is
  available, when oxygen is not available, they
  undergo fermentation.
• Some prokaryotes can use atmospheric nitrogen as
  a direct source of nitrogen in a process called
  nitrogen fixation. They convert N2 to NH4.

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Molecular Systematics Prokaryotic Phylogeny

• Molecular systematics is illuminating prokaryotic
  phylogeny.
• The first prokaryotes that were classified in the
  domain Archaea are known as extremophiles and
  live in extreme environments
• Extreme Halophiles live in saline environments.
• Extreme Thermophiles live in very hot
  environments.
• Other Archaea do not live in extreme
  environments.
• Methanogens use carbon dioxide to oxidize H2 and
  produce methane as a waste product.

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Ecological Importance of Prokaryotes

• Prokaryotes play crucial roles in the biosphere
• Many prokaryotes are decomposers, breaking down
  dead organic matter.
• Many prokaryotes are symbiotic, forming crucial
  relationships with other species.
• Some prokaryotes are pathogenic and cause illness
  by producing poisons. Antibiotics are chemicals
  that can kill prokaryotes. They are NOT
  effective against viruses.
• Many bacterial plasmids contain resistance genes
  to different antibiotics.

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Human Uses of Prokaryotes

• Prokaryotes are used by humans in many ways
• Prokaryotes are used in bioremediation, removing
  pollutants from soil, air, or water.
• Includes sewage treatment, oil spill clean up,
  and radioactive material precipitation.
• Prokaryotes are symbionts in the gut, and can be
  used to make vitamins, and assist in digesting
  food.
• Prokaryotes are used in gene cloning and
  producing transgenic organisms.
• Prokaryotes are used in a wide variety of food
  productions cheese, yogurt, and other products.