Transcript Bacterial Cell Structure (continued)

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Ways to think about peptidoglycan
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Bacterial Cell Structure (continued)
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Gram negative cell wall
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Outer membrane
• Lipid bilayer membrane: Asymmetric
– Inner and outer leaflets
• Inner leaflet made of phospholipids; outer leaflet is
made of lipopolysaccharide (LPS)
• LPS = endotoxin
– Proteins for transport of substances
• Porins: tri-subunit, transmembrane proteins
– Barrier to diffusion of various substances
• Lipoprotein: anchors outer membrane to PG
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Structure of LPS
extends from cell
surface.
contains odd
sugars e.g.
KDO.
Gln-P and fatty acids
take the place of
phospholipids.
www.med.sc.edu:85/fox/ cell_envelope.htm
Periplasmic Space
www.arches.uga.edu/~emilyd/ theory.html
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Periplasm
• The periplasm is the “stuff” in
that space,
– A hydrated gel including the PG
– Binding proteins that aid in
transport
– Hydrolytic enzymes for breaking
down large molecules
– Chemoreceptor proteins that help
direct swimming
– Enzymes for synthesizing PG, OM
• Must be in Gram + bacteria also.
Glycocalyx: capsules and slime layers
“Sugar covering”: capsules are firmly
attached, slime layers are loose.
Multiple advantages to cells:
prevent dehydration
absorb nutrients
cell
capsule
protection from predators, WBCs
protection from biocides (as part of biofilms)
attachment to surfaces and site of attachment by others.
www.activatedsludge.info/ resources/visbulk.asp
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Non-Carbohydrate layers
• S Layers
– Crystalline, protein layers
– Found widely in Archaea, also in G- and G+
• Polypeptide capsule
– B. anthracis has a poly D-glutamic acid capsule
TEM image of a freeze-etching preparation of a
bacterial cell exhibiting an S-layer with square
(p4) lattice symmetry. Bar, 100nm
http://www.nano.boku.ac.at/1143.html?&L=1
Fimbriae and pili
Both are appendages made of
protein
Singular: fimbria, pilus
Both used for attachment
Fimbriae: to surfaces (incl. host
cells) and other bacteria.
Pili: to other bacteria for
exchanging DNA (“sex”).
www.ncl.ac.uk/dental/oralbiol/ oralenv/images/sex1.jpg
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Fimbriae and pili-2
http://www.mansfield.ohio-state.edu/~sabedon/006pili.gif
Flagella
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•Flagella: protein appendages for
swimming through liquid or across wet
surfaces.
•Rotate like propellers.
•Different from eukaryotic flagella.
Arrangements on cells:
polar,
Lophotrichous,
amphitrichous,
peritrichous.
www.ai.mit.edu/people/ tk/ce/flagella-s.gif
www.bmb.leeds.ac.uk/.../icu8/ introduction/bacteria.html
From the membrane in: the bacterial cytoplasm
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• Cytoplasm is a gel made of
water, salts, LMW molecules,
and lots of proteins.
• DNA = nucleoid, w/ proteins
• Plasmids = small circular DNA
• Ribosomes: site of protein
synthesis.
Cytoplasm may also contain inclusions, gas vacuoles,
extended membrane systems, or magnetosomes.
But generally NO membrane-bound organelles.
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Inclusions and granules
• Storage molecules found as
small bodies within cytoplasm.
• Can be organic (e.g. PHB or
glycogen) or inorganic (Sulfur,
polyphosphate.
– PHB, a type of PHA,
degradable plastic
(polyester); glycogen, a
polymer of glucose.
– Sulfur, a metabolic byproduct; polyphosphate,
polymer of PO4
http://www.accessexcellence.org/WN/SUA12/marg499.html
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Magnetosomes
Magnetospirillum
magnetotacticum
“Membrane”- coated pieces of
magnetite, assist bacteria in
moving to microaerophilic
environments. An organelle?
North is down.
www.calpoly.edu/~rfrankel/ mtbphoto.html
http://geoweb.tamu.edu/courses/geol101/lab/topo_maps/IMG00006.GIF