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Bacterial Cell Structure (continued)
You are here.
Peptidoglycan structure
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•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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Outer membrane
• 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
Periplasmic Space
www.arches.uga.edu/~emilyd/ theory.html
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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
cell
capsule
protection from predators, WBCs
protection from biocides (as part of biofilms)
attachment to surfaces and site of attachment by others.
S-layers are highly structured protein layers that function like
capsules
www.activatedsludge.info/ resources/visbulk.asp
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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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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
Prokaryotic vs. eukaryotic flagella
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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
http://www.bgu.ac.il/~aflaloc/bioca/motil1.gif
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Spirochetes have internal flagella
• Axial filament: a bundle of internal flagella
– Between cell membrane and outer membrane
in spirochetes
– Filament rotates, bacterium corkscrews
through medium
Some bacteria move without flagella
• Gliding
– No visible structures, requires solid surface
– Slime usually involved.
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Axial filaments
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
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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
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 by-product;
polyphosphate, polymer of PO4
www.qub.ac.uk/envres/EarthAirWater/ phosphate_removal.htm
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Magnetosomes
Membrane coated pieces of
magnetite, assist bacteria in
moving to microaerophilic
environments. An organelle?
North is down.
Magnetospirillum
magnetotacticum
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
Only eukaryotes.
Both prokaryotes and
eukaryotes.
http://bio.winona.msus.edu/bates/genbio/images/endocytosis.gif
http://www.gla.ac.uk/~jmb17n/Teaching/JHteaching/Endocytosis/figures/howdo.jpg
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How molecules get through the membrane
Small molecules like
gases can diffuse
through the bilayer.
Larger or more
hydrophilic molecules
require transport
proteins.
Active transport
requires
metabolic energy.
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Review of eukaryotic cells
Mitochondrion
Plasmalemma (cell membrane)
nucleus, ribosomes
lysozome
endoplasmic reticulum
golgi body
www.steve.gb.com/ science/cell_biology.html