Post on 14-Apr-2018
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Prokaryotic Cell Structure
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The Prokaryotic CellMajor Structures
Cytoplasmic membrane
Cell wall
Cytoplasm
Inclusions
Nucleoid
Glycocalyx
Flagella
Pili & fimbrae
Endospores
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The Cytoplasmic MembraneOverview
~ 8 nm thick
Completely surround the
cell
Establishes the integrity ofthe cell
Selective barrier
Contains integral
membrane proteins Highly ordered yet
relatively fluid (fluid
mosaic)
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Cytoplasmic MembraneThe Phospholipid Bilayer
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Cytoplasmic MembraneUnit Membranes
Ectothiorhodospira halochloris photosynthetic membrane stacks
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The Cytoplasmic MembraneStructure
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The Cytoplasmic MembraneFunction
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The Cell Wall of Prokaryotes
Provides shape, rigidity
Keeps bacterial cells from lysing due to
internal turgor pressure
Two major types
Gram-negative: multilayered, complex
Gram-positive: single layer, thicker
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Cell Walls of Bacteria
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The Gram-Positive Cell Wall
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The Cell Wall of ProkaryotesThe Gram-Negative Outer Membrane
A second lipid layer
Contains polysaccharide
and protein
Lipid and polysaccharidelinked to form
lipopolysaccharides
Often called the
lipopolysaccharide layeror LPS.
Lipid A = endotoxin
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The Gram-Negative Cell Wall
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The E. coliNucleoid
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Bacterial Flagella
Long, thinappendages free atone end and attachedto the cell at the other
end. ~ 20 nm in diameter
Flagellar arrangement Polar
Lophotrichous Perithrichous
Flagellin: proteinsubunit of flagella
Peritrichous
Polar
Lophotrichous
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Flagellar Arrangements
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Structure of the Prokaryotic Flagellum
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Bacterial Cell Surface StructuresFimbriae & Pili
Both structurally similar to flagella but not
involved in movement
Fimbriae
Much shorter than flagella
Inherited trait
Enable cell to adhere to surfaces, formpellicles or biofilms
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Bacterial Cell Surface StructresFimbriae & Pili
Pili
Similar structurally to fimbriae but longer
Only one or two per cell
Serve as receptors for certain viruses
Involved in the process of conjugation
Involved in attachment of certain pathogenic
bacteria to tissues
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Fimbrae & Pili
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E. coliPilus
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Bacterial Cell Surface StructuresCapsules & Slime Layers
Glycocalyx: the polysaccharide material lying
outside the cell
Capsule: a rigid, tight matrix that can exclude
particles Slime layer: easily deformed, does not exclude
particles, hard to see
Functions
Attachment of pathogens Protection from phagocytosis
Resistance to desiccation
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Bacterial Capsules
Acinetobactersp. (negative stain) Rhizobium trifoli
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Endospores
Differentiated cells formed
within the vegetative cell
(sporangium)
Highly resistant to heat,
drying, radiation, acids,
chemical disinfectants
Bacillus, Clostridium
Dormancy maintained for
long periods