Prokaryotes bacteria

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Chapter27

• Prokaryotes (bacteria archaea)

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Domains and kingdoms

• The Kingdom Monera includes all prokaryotic
  celled organisms
• The bacteria and Archaea
• The Domains separate the bacteria and the Archaea
  (archaebacteria)
• The three domains are Bacteria, Archaea, and
  Eukarya

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Introduction

• Microscopic
• Found almost everywhere (ubiquitous)
• Vast numbers exist on earth
• Found thriving in extreme conditions
• Exhibit a wide variety of metabolic types
• Perform many essential functions for other
  organisms

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Structure, function, genetics

• Unicellular but, may aggregate into colonies
• Microscopic (average 1-5 micrometers)
• The most common shapes are
• Spheres (cocci, coccus)
• Rods (bacilli, bacillus)
• Spirals (spirochete, spirillus)

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Structure

• The Inside thick liquid is the cytoplasm. It
  contains water, electrolytes, nutrients, wastes,
  metabolic intermediates
• The DNA (chromosome) is not within a nucleus but,
  exposed to the cytoplasm
• Ribosomes are in the cytoplasm
• The cell (plasma) membrane is made of lipids and
  proteins and encloses the cytoplasm
• The cell membrane is surrounded by the cell wall

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Prokaryotic cell walls

• Protect the cell
• Gives the cell its shape
• Made of peptidoglycan
• Still allows movement of substances into and out
  of the cell
• Two major types
• Gram negative Gram positive

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Prokaryotic cell walls

• All bacteria will stain either Gram (purple) or
  Gram (pink)
• Used to classify bacteria
• The way they stain is a result of their cell wall
  structure
• It also can tell about the characteristics of
  bacteria

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Gram negative

• Has a relatively thin layer of peptidoglycan
• Has an outer membrane surrounding the
  peptidoglycan
• In general, more resistant to antibiotics
• Substances in outer membrane are toxic
• Outer membrane helps Gm- evade the immune system

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Gram positive

• Has a thicker layer of peptidoglycan
• Does not have an outer membrane
• In general, easier to treat with antibiotics
• However, some GM bacteria are very difficult to
  treat with antibiotics

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Structures in some bacterial species (capsules)

• If present, capsules are located outside of the
  cell wall
• Made of polysaccharide or protein
• Allows adherence to each other or substrates
• Protects from the host immune system or
  dehydration

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Structures in some bacterial species (fimbriae or
attachment pili)

• If present, they extend from the cell membrane to
  the outside of the cell
• Numerous, short, hair-like, protein appendages
• Allows adherence to each other or substrates
• Shorter and more numerous than flagella

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Structures in some bacterial species (flagella)

• If present, they extend from the cell membrane to
  the outside of the cell
• One or many, long, whip-like, protein appendages
• Allows for motility
• Longer than fimbriae
• Chemotaxis

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Internal structures

• Cytoplasm
• No organelles
• No nucleus
• One, small, circular, chromosome
• May have plasmids
• Have smaller ribosomes

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Internal structures (endospores)

• Only in some bacterial species
• A tough, resistant, structure that allows some
  bacteria to survive harsh conditions
• Forms inside the cell when conditions deteriorate
• Contains bacterial genetic material enzymes
• Cell ruptures and releases the endospore
• Endospore remains alive but, dormant indefinitely
• When conditions improve, endospore germinates and
  grows into a bacterium

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Prokaryotic reproduction (asexual)

• Most often, bacteria reproduce themselves
• The process is called binary fission
• The bacteria replicates its chromosome
• The bacteria divides into to cells each with one
  chromosome
• This is fast but, produces clones (genetically
  identical)

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LE 12-11_3
Cell wall
Origin of replication
Plasma membrane
E. coli cell
Bacterial chromosome
Chromosome replication begins. Soon thereafter,
one copy of the origin moves rapidly toward the
other end of the cell.
Two copies of origin
Origin
Origin
Replication continues. One copy of the origin is
now at each end of the cell.
Replication finishes. The plasma membrane grows
inward, and new cell wall is deposited.
Two daughter cells result.
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Prokaryotic reproduction (sexual, called
conjugation)

• Produces genetic diversity
• Two bacteria of similar species join by a tube
  called a sex pili
• The donor cell donates DNA to the other cell
  through the sex pili
• The recipient cell incorporates the new DNA into
  its chromosome
• The new genes may code for things that help the
  bacteria survive (antibiotic resistance, toxins,
  capsules)

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Prokaryotic metabolic types

• Heterotrophs
• Phototrophs
• Chemotrophs
• Autotrophs

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Oxygen needs of prokaryotes

• Obligate aerobes
• Obligate anaerobes
• Facultative anaerobes
• Aerobic respiration
• Anaerobic respiration

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Benefits of prokaryotes

• Nitrogen fixation
• Decomposition
• Removal of CO2
• O2 production
• Food source

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Pathogenic bacteria

• Cause diseases by
• Exotoxins
• Endotoxins
• Digestive enzymes
• Blockage