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8/9/2019 Microscopy & Cell Structure
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Microscopy and
Cell Structure
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Typical Bacterial Shapes
Also Pleomorphic Bacteria, which vary in their shape(e.g., Corynebacterium).
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Typical Bacterial Arrangements
streptococci
sarcina
staphylococci
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Prokaryotic
Cell Structures
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Typical Prokaryotic Cell
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CytoplasmicM
embra
ne
Movement across membrane for many substancesis controlled by membrane proteins.
Escherichia colihas >200 membrane proteins. Many of these proteins are involved in transport
across membranes.
Others of these proteins allow a bacterium to senseits surrounding environments(e.g., as in chemotaxis). Movement is via:
Simple Diffusion (including osmosis)
Facilitated Diffusion (with concentrationgradient & no energy expended)
Active Transport (against concentrationgradient & energy expended)
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SimpleDiffusion
--Osmosis
solute
molecules/ions
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CytoplasmicM
embra
ne
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Protein-
Mediate
dTransport
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ActiveTra
nsport
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The Prokaryotic Cell Wall
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The Prokaryotic Cell Wall
Determines cell
shape.
Prevents osmotic
lysis.
In some cases
recognized by host
immune system.
Target for
antibiotics.
Part of cell
envelope.
In Bacteria,composed of
Peptidoglycan.
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Gram-Pos vs. Gram-Neg.
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Gram-Positive Cell Envelope
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Gram-NegativeC
ellEnvelope
cell wall
endotoxin
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Gram-Negative Cell Envelope
Periplasm: Site
of preliminary
nutrientdegradation.
LPS: Protection from
antibiotics such as
penicillin plus againstcertain toxins.
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Lipopo
lysaccha
ride(LPS)
Lipid A =Endotoxin
Carbohydrate has
negative charge andprovides protection
against some
antibiotics & some
toxins (e.g.,
detergents).
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Mycoplasmalac
kCellWalls
Note:Pleomorphic
Mycoplasma pneumoniae causesWalking Pneumonia
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Glycocalyx
Protection (e.g.,
Streptococcuspneumoniae from
phagocytosis)
Attachment (e.g.,
Streptococcus
mutans causing
dental plaques)
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Ca
psuleStaining
Capsules are moreregular and
gelatinous.
Slime Layers are
less regular and
more diffuse.
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Bacteria Flagella (plural)
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Flage
llarArra
ngemen
ts
also atrichous
e.g.,E. coli
Polar
Flagellum
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Chemot
axis
Also
Phototaxis,etc.
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Pili (sing. Pillus)
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Closed Circular Chromosome
Also Plasmids, which are
smaller, circular pieces of
DNA.
Plasmids usually
encodeexpendablefunctions, e.g.,
antibiotic
resistance.
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