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Cell envelope G(+) vs G(-)
- G(-) has three layers
- inner membrane (cell membrane)
- cell wall (thin)
- outer membrane
- G(+) has two layers
- cell membrane
- cell wall (very thick)
- no outer membrane exists
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Characterize bacteria by temperature requirement
- low or high
- Some bacteria like E. coli can grow at higher than body temperature, 42 degrees Celsius, but other bacteria cannot. If a bacteria can’t grow at 42 degrees Celsius, it’s not E. coli.
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Characterize bacteria by nutritional requirement
- sugar utilization - glucose, lac, gal, etc.
- gas/acid production - H2S, Co2, lactic acid, etc.
- main criterion before mol biol development
- test by planting on an array/panel of diff sub, + or -, indexed in catalog
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Characterize bacteria by O2 requirement
- Aerobes: need O2
- Facultative anaerobes: can live w/ or w/o O2; most bacteria fall in this category
- Strict anaerobes: poisoned by O2; convert to spore in environment w/o O2; back to vegetative state when no O2
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Sequencing of bacterial genome
- 1995 - first bacteria, Haemophilus influenzae (cost ~1yr, millions $; not the cause of flu)
- 2004 - 300
- 2014 - 30,000
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Molecular identification of bacteria - fingerprint based on _______ signature sequence
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Why use 16S rRNA?
- essential for all living organisms
- chages little overtime (very conserved; the distance/difference represents evolutionary distance; eukaryotes, archaea, prokaryotes (bacteria))
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Functions of cell membrane
- permeability barrier
- protein anchor - secretion systems
- energy conservation
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Composition of cell membrane
phospholipid bilayer
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Cell wall functions
- prevents cell from bursting (rigid)
- maintains cell shape
- provides platform for appendages
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Cell wall composition - ________:
- Peptidoglycan
- N-acetypglucosamine (G) & N-acetylmuramic acid (M) form repeated sequence
- side chains coming off from M, made of -LAla-DGlu-DAP-DAla(-DAla) (DAP, diaminopimelic acid, on one chain attacks the DAla next to DAP in the other chain, kicking off the last DAla, forming peptide bond, catalyzed by peptidoglycan transpeptidase)
- Sugar chains form layers, peptide bridges make connections between the layers
- G(-): 4-5 layers
- G(+): 40-50 layers
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Cell wall is often used as the target for _______, at the same time, its composition is subject to ______ hence _____ is developed.
- antibiotic
- mutation
- drug resistance
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Linkage between G-M is _____, which is sensitive to ________, found in _____.
- β1,4-linkage
- lysozome
- saliva
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G(-) outer membrane
- phospholipid single layer w/ the hydrophilic side facing inward (cell wall)
- Lipopolysaccharide (LPS) connect to the hydrophobic side of phospholipid
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LPS in G(-) outer membrane
- lipid A: contains fatty acid and sugars, such as GlcN, which can be different depending on the bacteria, attached to the phospholipid tails
- core polysaccharide (rough core): keto-deoxy-octanoate (KDO, only found in LPS) and other sugars form polisaccharide branched chains
- O antigen (O-polysaccharide): most outside; long, linear polysaccharide consisting of many repeating saccharide sequences of 4 to 7 sugars.
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Lipid A
- endotoxin
- causes toxic shock syndrome, happens when infected by a lot of bacteria
- Sometimes LPS itself is called endotoxin, but it’s the Lipid A component that is
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O-antigen
- immunogenic.
- different O-antigens define serotypes
- each strain contains any genetic mutation
- diff serotype -> diff strain
- diff strain may have same serotype
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Why would a bacteria change or have so many different Oantigens?
Evade host immune system, body makes antibodies that target the strain, and this allows bacteria to evade them
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