Transcript Effect of osmotic pressure on cells

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Bacterial Cell Structure (continued)
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Peptidoglycan structure
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Bacteria and Osmotic pressure
• Bacteria typically face hypotonic environments
– Insides of bacteria filled with proteins, salts, etc.
– Water wants to rush in, explode cell.
• Peptidoglycan provides support
– Limits expansion of cell membrane
– Growth of bacteria and mechanism of penicillin
• Bacteria need other protection from hypertonic
situations
– Water leaves the cell; cell membrane shrinks
– Lack of water causes precipitation of molecules, death
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Effect of osmotic pressure on cells
• Hypotonic:
water rushes in;
PG prevents cell
rupture.
• Hypertonic:
water leaves
cell, membrane
pulls away from
cell wall.
In this example, the ENVIRONMENT
relative to the inside of the cell.
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Cell Wall Exceptions
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• Mycobacterium and relatives (Gram + cells)
– Wall contains lots of waxy mycolic acids
– Attached covalently to PG
• Mycoplasma: no cell wall
– Parasites of animals, little osmotic stress
• Archaea, the 3rd domain
– Pseudomurein and other chemically different wall
materials (murein another name for PG)
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: 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, present in Gram +
bacteria also.
– 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
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Glycocalyx: capsules and slime layers
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“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
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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Protein appendages used
for locomotion.
Made of subunits
Rotate like propellers.
Different from eukaryotic flagella.
Arrangements on cells:
polar, lophotrichous peritrichous.
www.ai.mit.edu/people/ tk/ce/flagella-s.gif
www.bmb.leeds.ac.uk/.../icu8/ introduction/bacteria.html