Microbiology - L2 - Cell Envelope

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  1. 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
  2. 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.
  3. 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
  4. 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
  5. Sequencing of bacterial genome
    • 1995 - first bacteria, Haemophilus influenzae (cost ~1yr, millions $; not the cause of flu)
    • 2004 - 300
    • 2014 - 30,000
  6. Molecular identification of bacteria - fingerprint based on _______ signature sequence
    • 16S rRNA
    • S: Svedberg unit
  7. Why use 16S rRNA?
    • essential for all living organisms
    • chages little overtime (very conserved; the distance/difference represents evolutionary distance; eukaryotes, archaea, prokaryotes (bacteria))
  8. Functions of cell membrane
    • permeability barrier
    • protein anchor - secretion systems
    • energy conservation
  9. Composition of cell membrane
    phospholipid bilayer
  10. Cell wall functions
    • prevents cell from bursting (rigid)
    • maintains cell shape
    • provides platform for appendages
  11. 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
    • Image Upload 1
  12. 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
  13. Linkage between G-M is _____, which is sensitive to ________, found in _____.
    • β1,4-linkage
    • lysozome
    • saliva
  14. G(-) outer membrane
    • phospholipid single layer w/ the hydrophilic side facing inward (cell wall)
    • Lipopolysaccharide (LPS) connect to the hydrophobic side of phospholipid
  15. 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.
  16. 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
  17. O-antigen
    • immunogenic.
    • different O-antigens define serotypes
    • each strain contains any genetic mutation
    • diff serotype -> diff strain
    • diff strain may have same serotype
  18. 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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Microbiology - L2 - Cell Envelope
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Microbiology - L2 - Cell Envelope
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