Dr. Alvin Fox

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The Bacterial Cell
Dr. Alvin Fox
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Key Words
Prokaryotic
Outer membrane
Eubacteria (Bacteria)
Periplasmic space
Oxidative phosphorylation
Eukaryotic
Spheroplast/protoplast
Plasmid
Flagella
Chromosome
Chemotaxis
Ribosome
Axial filament
Peptidoglycan (murein, mucopeptide)
Periplasmic binding protein
Gram stain
Permeases
Gram negative
Storage Granules
Gram positive
Pili (fimbriae)
Cell envelope
Capsule (slime layer, glycocalyx)
Cell membrane
Endospore (spore)
Cell wall
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PROKARYOTES
EUKARYOTES
BACTERIA
ARCHAEA
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Prokaryotes (Bacteria)

• Eubacter "True" bacteria
• human pathogens
• clinical or environmental
• one kingdom
• Archaea
• Environmental organisms
• second kingdom

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Eukaryotes

• Other cell-based life e.g.
• plants
• animals
• fungi

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Prokaryotic Cell (versus Eukaryotic Cell)

• Not compartmentalized
• Cell membranes lack sterols (e.g. cholesterol)
• Single circular chromosome
• Ribosomal are 70S
• - subunits
• 30S (16S rRNA)
• 50S (5S 23S rRNA)

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Bacteria versus Archaebacteria

• Eubacteria
• peptidoglycan (murein)
• muramic acid
• Archaebacteria
• pseudomurein
• no muramic acid

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Bacteria versus Archaebacteria

• 16S rRNA
• sequence very different

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Eukaryotic cell
Prokaryotic cell
(e.g. animal)
Flagellum
Nucleoid
Cell wall
Cell membrane
Rough endoplasmic reticulum
Nucleus
Gram
Pili
Gram -
Granule
Capsule
Cell (inner) membrane
Outer membrane
Cytoplasm
Ribosomes
Mitochondria
Cell wall
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Bacteria

• Plasmids
• Extra-chromosomal DNA
• multiple copy number
• coding pathogenesis and antibiotic
• resistance factors
• bacterial replication

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The Cell Envelope
Gram Stain
Gram Positive
Gram Negative
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Oxidative phosphorylation occurs at cell
membrane (since there are no mitochondria).
Cytoplasm
Cell Wall
Cell membrane

• The cell wall is outside of cell membrane
• rigid, protecting cell from osmotic lysis.

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GRAM POSITIVE
Lipoteichoic acid
Peptidoglycan-teichoic acid
Cytoplasmic membrane
Cytoplasm
GRAM NEGATIVE
Lipopolysaccharide
Porin
Outer Membrane
Braun lipoprotein
Periplasmic space
Inner (cytoplasmic) membrane
Cytoplasm
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Outer Membrane

• Gram negative bacteria
• major permeability barrier
• space between inner and outer membrane
• periplasmic space
• store degradative enzymes
• Gram positive bacteria
• no periplasmic space

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GRAM NEGATIVE CELL ENVELOPE
Outer Membrane (Major permeability barrier)
Lipopolysaccharide
Porin
Braun lipoprotein
Periplasmic space
Degradative enzyme
Periplasmic binding protein
Permease
Inner (cytoplasmic) membrane
Cytoplasm
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GRAM POSITIVE CELL ENVELOPE
Degradative enzyme
Peptidoglycan-teichoic acid
Lipoteichoic acid
Cytoplasmic membrane
Cytoplasm
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FLAGELLA

• Some bacteria are motile
• Locomotory organelles- flagella
• Taste environment
• Respond to food/poison
• chemotaxis

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• Flagella
• embedded in cell membrane
• project as strand
• Flagellin (protein) subunits
• move cell by propeller like action

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Axial filaments

• spirochetes
• similar function to flagella
• run lengthwise along cell
• snake-like movement

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Making Wall-less forms

• Result from action of
• enzymes lytic for cell wall
• antibiotics inhibiting peptidoglycan biosynthesis
• Usually non-viable
• Wall-less bacteria that dont replicate
• spheroplasts (with outer membrane)
• protoplasts (no outer membrane).
• Wall-less bacteria that replicate
• L forms

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Naturally Wall-less Genus

• Mycloplasma

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Pili (fimbriae)

• hair-like projections of the cell
• sexual conjugation
• adhesion to host epithelium

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Capsules and slime layers

• outside cell envelope
• well defined capsule
• not defined slime layer or glycocalyx
• usually polysaccharide
• often lost during in vitro culture
• protective in vivo

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Endospores (spores)

• Dormant cell
• Produced when starved
• Resistant to adverse conditions
• - high temperatures
• - organic solvents
• contain calcium dipicolinate
• Bacillus and Clostridium