Prokaryotes

1
Prokaryotes

• Lack nuclei
• Typically lack or have very few internal
  membranes
• Cytoplasm contains ribosomes, storage granules
  that hold glycogen, lipid, or phosphate compounds
• Metabolic enzymes are associated with the plasma
  membrane, especially where it is infolded to form
  limited internal membranes such membranes are
  generally referred to as a mesosome
• The plasma membrane interacts with the cytoplasm
  in signaling functions
• Motile bacteria have a corkscrew flagellum

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Prokaryotic Organization

• Key features
• No nucleus
• DNA held in nucleoid
• Cytoplasm dense
• Ribosomes
• Storage granules
• Limited membranes
• Plasma membrane
• Corkscrew flagellum
• Cell wall is complex
• Outer membrane
• Peptidoglycan layer
• Capsule
• Pili extend from cytoplasm

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Domains of Life
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BACTERIA

• ARCHAEBACTERIA
• Introns in DNA
• Lack peptidogycan in cell walls
• Live in extreme environments

• EUBACTERIA
• Includes most bacteria
• Most have one of three shapes
• May be divided into up to 12 phyla
• Classification is controversial

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Archaebacteria and Eubacteria

• Carl Woese has indicated, based on small subunit
  ribosomal RNA (SSU rRNA) sequencing, that there
  are two domains of bacteria
• Archaea
• Lack peptidoglycan in cell wall
• Produce methane gas
• Ether-linked lipids
• Live in early Earth conditions
• Extreme halophiles, thermophiles, and acidophiles
• Eubacteria
• Have peptidoglycan in cell wall
• Are rifamycin-sensitive (blocks transcription)
• All other bacteria

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TYPES OF ARCHAEBACTERIA
Methanogens living in sewage
Thermoacidophilies Living in hot springs
Extreme halophile living in the Great Salt
Lake
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The Archaea

• Methanogens
• Anaerobes
• In digestive tracts of animals
• Produce methane gas
• Extreme halophiles
• Live in saturated salt
• Many are photosynthetic
• Extreme thermophiles
• Live in hot springs
• Often live in acidic environments (acidophiles)

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The Eubacteria

• Most abundant bacteria
• Important in the biosphere
• Major producer of primary production (of carbon
  via photosythesis)
• Most numerous organisms in the soil
• Most important nitrogen fixing organisms, often
  via symbiotic associations
• e.g. rhizobial bacteria in root nodules

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Bacteria

• Bacteria are prokaryotes
• They are cells
• They lack nuclei
• There are two professional viewpoints regarding
  the general, overall classification of
  prokaryotes
• Some biologists support the concept that they
  constitute two domains Archaea and Eubacteria
• Other biologists classify them into two kingdoms,
  Archaebacteria and Eubacteria
• Most are very small 0.5 1.0 mm in diameter

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BASIC SHAPES OF EUBACTERIA
ROD-SHAPED
SPIRILLA
SPHERICAL
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Cell Walls

• Provides support for cell
• Protects against osmotic shock
• Most bacteria well adapted to hypotonic
  conditions
• Most bacteria grow poorly in hypertonic
  conditions hence jams, salted foods prevent
  bacterial growth
• Cell wall composition unique to bacteria
• Eubacterial cell wall made of peptidoglycan
• Complex of polymerized amino sugars and short
  polypeptides
• Is really one polymer surrounding the cell

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Capsules and Pili

• Many bacteria secrete a capsule, or slime layer
• Used to attach, prevent phagocytosis
• Can be used to enhance infective bacteria
• Pili are hair-like appendages
• Allow attachment to surfaces
• Are sometimes involved in bacterial conjugation
  (sexual activity that involves the transfer of
  DNA)

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The Bacterial Flagellum

• Rotates
• Is corkscrew-shaped
• Three parts
• Basal body
• Hook
• Filament (made of one protein flagellin)
• Cell uses ATP to pump protons out
• Protons diffuse through membrane at basal body
• Breakdown of gradient converted to rotation

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The Gram Stain

• Bacterial cell wall differences can be used to
  identify and categorize cells
• 1888 Christian Gram developed the Gram Stain
• Some bacteria retain crystal violet stain after
  alcohol wash
• Called gram-positive
• Other cells referred to as gram-negative
• Stain retention determined by cell wall
  organization
• Gram-positive cells have thick peptidoglycan wall
• Gram-negative cells have outer membrane and thin
  peptidoglycan layer

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Gram-positive and Gram-negative Cell Walls
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Most Species of Eubacteria may be Grouped Based
on Staining

• Gram-Negative
• Lack thicker layer of peptidoglycan
• Stain pink
• Endotoxins

• Gram-Positive
• Thicker layer of peptidogycan
• Stain purple
• Exotoxins (released when bacteria die)

Gram-positive
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Giant Bacterium

• But size is not an indicator Epulopiscium
  fishelsoni is a giant bacterium from the gut of
  the surgeonfish
• Here, 600 mm long and 80 mm wide, much larger
  than the large protist Paramecium (other cells in
  picture)

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Nutrition and Growth

• Saprophtes ex decomposers
• Photoautotrophs ex blue-green algae
• Obligate anaerobes ex tetanus
• Facultative anaerobes ex E.Coli
• Obligate aerobes ex tuberculosis
• Thermophilic bacteria
• Most bacteria grow at at neutral pH but some grow
  best at a pH of 6 or lower
• Bacteria that produce yogurt and sour cream

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Anabaena a Eubacterium

• Complex, free-living photosynthetic
• A cyanobacterium
• The larger cells fix nitrogen, are
  oxygen-sensitive

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Bacterial Chromosome

• Bacteria have a circular genomic DNA molecule -
• Single chromosome
• 1000X longer than cell if stretched out
• Also have plasmids
• Small, circular DNA fragments
• Can replicate independently of the genomic DNA or
  be integrated into genomic DNA
• Carry genes for resistance, for genetic exchange
  or for enzymes

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Bacterial Sexual Reproduction

• Most simply put, sex is transfer of genetic
  information.
• Three mechanisms known for bacterial sexual
  reproduction
• Transformation
• Bacteria take up DNA from environment
• Griffiths 1928 experiment with S and R bacteria
  showed that DNA was heritable substance
• Transduction
• Genes are transferred through phage (next slide)
• Conjugation
• Two cells of opposite mating type come together,
  form pili bridges bridges through which DNA is
  transferred

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Conjugation of E. coli
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Bacterial Pathogens

• Some are disease-causing agents
• Most bacteria are not harmful
• Many have positive relationship with hosts e.g.
  human gut microbe E. coli
• But many are pathogenic
• Cause serious disease
• Cholera
• Diphtheria
• Tuberculosis

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Antibiotics

• Antibiotics are drugs that combat bacteria by
  interfering with cellular functions
• Penicillin interferes with cell wall production
• Tetracycline interferes with protein production
• Sulfa drugs produced in the laboratory
• Broad-spectrum antibiotics will affect a wide
  variety of organisms

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Endotoxins

• Pathogenic bacteria can produce exotoxins, which
  increase their success but tend to be very
  damaging to the host
• Often the toxin, not the bacterial infection, is
  most dangerous
• Examples
• Diphtheria toxin
• Botulism toxin
• Endotoxins
• Not secreted but are components of the cell wall
• Affect host when released from dead bacteria
• Can bind macrophage, cause the release of
  fever-inducing agents
• Resistant to heating

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Commercial Bacteria

• Bacteria used in many commercial processes
• Lactic acid bacteria convert lactic acid to
  simpler monomers
• Used in yogurt, acidophilous milk for
  lactose-intolerant people
• Bacteria used for making
• Cheeses
• Fermented meats such as salami
• Pickling agents such as vinegar
• Bacteria also used to make pharmaceutical agents
• Also used as means to make biomedical agents and
  biological molecules
• Used also to reduce pollution as bioremediation
  agents

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Penicillin

• This amazing fungus produces the famous
  antibiotic, penicillin. In 1928. Alexander
  Fleming observed that a mold called Penicillium
  notatum produced a substance, later known as
  penicillin, that killed bacteria in its presence.
  This antibiotic was the first of many to be found
  and used to treat infections.
• Interferes with cell wall production.

This fungus makes antibiotics and cheese. Other
varieties of the fungus produce blue cheese and
Roquefort cheeses.
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Kochs Postulates

• Robert Koch, late 19th Century
• Defined conditions likely to identify a pathogen
• Present in all infected individuals
• Sample of the micro organism can be grown in
  culture from the host
• Culture produces disease in a second host
• Microorganism can be recovered from second,
  experimentally created host