BIOL 201 - Lecture 4

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  1. What are the principal differences between Archaea and Bacteria?
    • rRNA nucleotide sequences– Cell wall and membrane lipids differ
    • • A key evolutionary (and ecological) feature?
    • Bacteria: – Are scarce in extreme environments – Can form endospores– Are associated with disease– Are more diverse in forms of energy acquisition (some can photosynthesize)
    • Bacterial cell walls always contain peptidoglycan, but in differing amounts
  2. What is the significance of the Gram stain response?
    • • Common diagnostic tool
    • • Gram +ves (A monophyletic group)– very resistant to osmotic stress– can form endospores– usually chemoheterotrophs– non-motile and without appendages
    • • Gram -ves (>9 different groups) – utilise periplasmic space for • Nutrient acquisition• Nutrient processing• Detoxifying environment
    • • G+ves and G-ves often found together in microbial communities in organisms, soils, water bodies….
  3. Some Gram+ bacteria can form highly resistant dormant structures
    • • Endospores: Gram positive only
    • – E.g. Clostridium andBacillus spp. such as botulism and anthrax
    • • Akinetes: Cyanobacteria
  4. Archaea
    • • Cell walls: No peptidoglycan, but may or may not retain G stain depending on wall thickness
    • • Membrane lipids: distinctive from both Bacteria and Eukarya in that lipid ‘tails’ are branched, and sometimes linked
    • • Transcriptional machinery more similar to eukaryotes (TATA binding, etc)
    • • 4 major functional groups:– Methanogens– Archaeal sulfate reducers– Extreme halophiles– Extreme thermophiles
    • But they are frequent in soils, freshwater and marine environments
  5. energy/nutritional groups of prokaryotes
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  6. Chemoheterotrophs: Saprobes = “The Decomposers/Recyclers”
    • Energy and carbon supplied from organic compounds
    • • Saprobes exist on non-living matter (e.g. Actinomycetes (such as Streptomyces), Azotobacter, Clostridium)
    • • Metabolic product of one bacterial species is often the substrate for another (examples ahead)
    • • Antibiotic production common
  7. Anaerobic chemoheterotrophy: Fermentation
    • Respiration: Glucose + O2-> Energy + H2O + CO2Many bacteria (and archaea) evolved in, and thrive in, low oxygen environments
    • Fermentation: When O2is low, chemical energy isoften released by metabolising pyruvate to: -Lactate by bacteria and archaea - Ethanol by fungi and plants
  8. Bacterial roles in food production
    • – Lactobacteria (lactose –> lactic acid fermenters)• Milk products: Yogurt, Cheddar cheese, Mozzarella, Cottage cheese, cheese curds, Buttermilk……• Beers: Belgian ‘lambic style’ and Wheat beers• Bread: Sourdough• Pickled vegetables–
    • Malo-lactic fermenters• Some Wines: Alsace and N American whites. Benefit from Malic to Lactic conversion that reduces acidity
    • – Acetic acid fermenters (e.g. Acetobacter) Vinegar
    • – Propionibacterium: E.g ‘eyes’ in ‘Swiss’ cheese
  9. Chemoheterotrophic symbionts: e.g. Rumen bacteria and archaea
    • • Rumen: A specialised stomach containing prokaryotic cultures
    • • An anaerobic culturing hotspot for prokaryotes
    • • Eat twice –regurgitate fermented cud
    • • Plant leaf and shoot material often dominated by cellulose
    • • Prokaryotes and fungi produce cellulases
    • • Cellulose -> (by cellulase) Glucose -> (via Fermentation) Acetate and fatty acids
    • > Absorption into bloodstream for aerobic respiration by host animal
    • > (via Methanogenesis) CH4in some animals
    • eg. Legumes and Alder
  10. Chemoheterotrophs: Pathogenic and parasitic bacteria
    Some animal hosts: PneumoniaLeprosyTetanusCholeraListeriosisSyphilis…
  11. Photoautotrophs
    • Cyanobacteria (“Blue green algae”):
    • CO2+ 2H20 (CH2O) n+ H20 + O2
    • Purple and Green Sulfur bacteria:
    • CO2+ 2H2S (CH2O) n+ H20 + 2S
  12. Cyanobacteria
    • Pigments - chlorophyll a, phycobilins(phycocyanin, phycoerythrin)
    • Resting stages - Akinetes
    • Ability to fix nitrogen – Heterocysts
    • Critical roles in:evolution of lifeglobal C and N cycles
    • Storage capacities for C (glycogen), P and N
    • Many symbiotic forms
    • Stromatolites
  13. Chemoautotrophs
    • Energy by oxidising sources such as NH4, Fe2+, S, HS-, CH4, H2 while fixing CO2for carbon
    • • Nitrifiers: NH4-> Nitrate
    • • Iron oxidisers: Fe2+ -> Fe3+
    • • Sulfur oxidisers: S -> SO2-
    • • Methanotrophs: CH4-> CO2
    • • Some methanogens: H2-> CH4
    • • Globally important biogeochemical transformations
  14. Methanogens
    • • Only in the Archaea
    • • Strictly anaerobic metabolism
    • • Some methanogens are autotrophs, some are chemoheterotrophs (acetate ->CH4)
    • • Natural gas (methane is odourless)
    • • Methane a very important greenhouse gas
  15. Photoheterotrophs
    • A purple nonsulfur bacterium, Rhodospirillum rubrum. Grown in low light, this individual has developed many photosynthetic pigments.
    • Extraordinary metabolic flexibility… OR chemoheterotrophy (+/-O2)Occur in mud and water of lakes, ponds and seashores where there is abundant organic matter and little sulfur (e.g. sewage polluted lakes)

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BIOL 201 - Lecture 4
2011-09-29 18:11:40

prokaryotes (2)
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