Bacterial Cell Structure (continued)
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Peptidoglycan structure
•Bacteria typically face hypotonic environments
•Peptidoglycan provides support,
Limits expansion of cell membrane
•Bacteria need other protection from hypertonic situations

Gram negative cell wall
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• Lipid bilayer membrane
– Inner and outer leaflets
• Inner leaflet made of phospholipids; outer leaflet is made of lipopolysaccharide (LPS)
• LPS = endotoxin
– Proteins for transport of substances
• Porins: 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
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Periplasmic Space 6 www.arches.uga.edu/~emilyd/ theory.html

Periplasmic space:
• A lot like cytoplasm, with
– Peptidoglycan layer
– Proteins that aid in transport
– Proteins that break down molecules
– Proteins that help in synthesis.
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Glycocalyx: capsules and slime layers
“Sugar covering”: capsules are firmly attached, slime layers are loose.
Multiple advantages to cells: prevent dehydration absorb nutrients capsule protection from predators, WBCs protection from biocides (as part of biofilms) cell attachment to surfaces and site of attachment by others.
S-layers are highly structured protein layers that function like capsules
8 www.activatedsludge.info/ resources/visbulk.asp

Fimbriae and pili
Both are appendages made of protein
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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

Flagella
•Flagella: protein appendages for swimming through liquid or across wet surfaces.
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•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

Prokaryotic vs. eukaryotic flagella 11
Prokaryotic flagella :
•Made of protein subunits
•Protrude through cell wall and cell membrane.
•Stiff, twirl like a propeller
Eukaryotic flagella :
•A bundle (9+2) of microtubules (made of protein)
•Covered by cell membrane
•Whipping action www.scu.edu/SCU/Departments/ BIOL/Flagella.jpg
img.sparknotes.com/.../monera/ gifs/flagella.gif

Chemotaxis
• Bacteria change how they move in response to chemicals
• Bacteria move toward attractants
(e.g. nutrients).
• Bacteria move away from repellants.
• In this figure, bacteria use up nutrients in the agar, then move outward to where more nutrients are, producing rings of growth.
http://class.fst.ohio-state.edu/fst636/SP2004_mustafa/chemotaxis%20demo_SP04.htm
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Runs and Tumbles: bacteria find their way
13 http://www.bgu.ac.il/~aflaloc/bioca/motil1.gif

Spirochetes have internal flagella
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Axial filament: a bundle of internal flagella
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Between cell membrane and outer membrane in spirochetes
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Filament rotates, bacterium corkscrews through medium
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• Gliding
– No visible structures, requires solid surface
– Slime usually involved.

Axial filaments
15 http://images.google.com/imgres?imgurl=http://microvet.arizona.edu/Courses/MIC420/lecture_notes/spirochetes/gifs/spirochete_crossection.gif& imgrefurl=http://microvet.arizona.edu/Courses/MIC420/lecture_notes/spirochetes/spirochete_cr.html&h=302&w=400&sz=49&tbnid=BOVdHqe pF7UJ:&tbnh=90&tbnw=119&start=1&prev=/images%3Fq%3Daxial%2Bfilament%2Bbacteria%26hl%3Den%26lr%3D%26sa%3DG

Gliding Motility 16
Movement on a solid surface.
No visible organelles of locomotion.
Cells produce, move in slime trails.
Unrelated organism glide: myxobacteria, flavobacteria, cyanobacteria; appear to glide by different mechanisms.
Cells glide in groups, singly, and can reverse directions.
www.microbiology.med.umn.edu/ myxobacteria/trails.jpg

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From the membrane in: the bacterial cytoplasm
• 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 by-product; polyphosphate, polymer of PO
4 www.qub.ac.uk/envres/EarthAirWater/ phosphate_removal.htm

Magnetosomes
Membrane coated pieces of magnetite, assist bacteria in moving to microaerophilic environments. An organelle?
North is down.
Magnetospirillum magnetotacticum
19 www.calpoly.edu/~rfrankel/ mtbphoto.html

How things get in (and out) of cells
• Eukaryotic cells
– Have transport proteins in membrane
– Have a cytoskeleton made of microtubules
• Allows for receptor mediated endocytosis, phagotcytosis, etc.
• Cell membrane pinches in, creates vesicle
• Prokaryotic cells
– Have very little cytoskeleton
– Can NOT carry out endocytosis
– Entry of materials into cell by diffusion or transport processes ONLY.
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Illustrations: entry into cells
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Both prokaryotes and eukaryotes.
Only eukaryotes.
http://bio.winona.msus.edu/bates/genbio/images/endocytosis.gif
http://www.gla.ac.uk/~jmb17n/Teaching/JHteaching/Endocytosis/figures/howdo.jpg

How molecules get through the membrane
Small molecules like gases can diffuse through the bilayer.
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Larger or more hydrophilic molecules require transport proteins.
Active transport requires metabolic energy.

Review of eukaryotic cells
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Mitochondrion
Plasmalemma (cell membrane) nucleus, ribosomes lysozome endoplasmic reticulum golgi body www.steve.gb.com/ science/cell_biology.html