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Chapter 13 Lecture Outline
Energetics and Catabolism
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Building the Cell Catabolism Breaking down molecules for energy Anabolism Using energy to build cell components Reducing entropy, creating order Metabolism Balance between catabolism and anabolism Central biochemical pathways used for both TCA cycle, glycolysis, pentose phosphate shunt Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Metabolism Sunlight Reduced geological compounds (rocks, inorganic compounds) (Reduced) biological macromolecules (starch, fats) (Major energy source today) (Energy source for animals) (First energy source) Phototrophy Lithotrophy Organotrophy ANABOLISM CATABOLISM Long-term energy storage Energy Short-term energy storage Biosynthesis Carbon, nitrogen, water ATP Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Catabolism Always Generates Heat
Illustrated in microbial composting Actinomycetes digest wood and newspaper Thermophiles take over compost digestion at °C
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Refresher Carbon source for biomass Energy source Electron source
Auto- Hetero- Energy source Photo- Chemo- Litho- Organo- Electron source
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Chemotroph Only in archaea Phototroph
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Electron Transfer Major source of cell energy Passage of electrons releases energy Requires electron donor, electron acceptor Electron transport found in all cells Different donors, acceptors Electron energy can be stored Reduced chemicals Concentration gradient Phosphorylation of chemicals Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Energy Carriers ATP NADH NADPH FADH2
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Catabolism: The Microbial Buffet
Microbes have great catabolic diversity Electron donors Lithotrophy: inorganic molecules Organotrophy: organic molecules Phototrophy: use light energy to reduce compounds, then use these as electron donor Electron acceptors Respiration: inorganic molecules are terminal electron acceptors Aerobic: oxygen Anaerobis: other inorganic compounds, e.g. nitrate Fermentation: organic molecules are terminal electron acceptors Chemotrophy Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Organotrophy Wide range of organic compounds digested Polysaccharides Converted to glucose Lipids Converted to acetyl-CoA And glycerol Amino acids Aromatic compounds Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Glucose metabolism Fermentation Respiration
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Glucose Metabolism Glucose pyruvate Three pathways EMP ED PPS
Many bacteria, archaea, eukaryotes ED Enteric bacteria PPS
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Glucose metabolism Fermentation Respiration
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Fermentation Completes glucose metabolism Glucose is oxidized NADH is reduced Must be reoxidized to NAD+ + H+ Pyruvate product builds up Must be eliminated In the absence of oxygen Pass electrons back to pyruvate or to Acetyl-CoA produced from pyruvate Convert pyruvate into other products Useful for cell, or easy to eliminate Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Fermentation Examples
S. cerevisiae (baker’s yeast) Decarboxylate pyruvate CO2 produced causes bread to rise Reduce acetaldehyde to ethanol Vertebrate muscles Lactate buildup, reoxidized when O2 present E. coli Mixed fermentation produces formate, acetate Propionibacterium CO2 produced makes holes in cheese Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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Swiss Cheese (Emmentaler)
Fermentation product of Propionibacterium freudenreichii Lactate Propionate, acetate, and CO2
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Glucose metabolism Fermentation Respiration
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Respiration Complete oxidation of pyruvate/acetylCoA to CO2 and H2O
Pyruvate = glycolysis product AcCoA = lipid oxidation product Utilizes TCA (tricarboxylic acid) cycle Typically with inorganic electron acceptor Respiration produces more energy than fermentation Maximal 38 ATPs Fermentation up to 2 ATPs conducted only when no inorganic acceptor present
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Aromatic Catabolism Bacteria can degrade many compounds Pseudomonas, Rhodococcus Aromatic compounds converted to pyruvate Allows growth in wide range of environments Used for bioremediation Cleaning up oil spills Cleaning industrial sites Degrading toxic compounds Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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As a Whole Bacteria Can Metabolize Almost Any Compound
Extracellular polysaccharides Bacterium CJ2 Catabolizes the pollutant napthalene
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Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
Concept Quiz What do fermentation and the TCA cycle have in common? They both oxidize pyruvate. They both produce energy. They both eliminate waste pyruvate. Answer: D Microbiology: An Evolving Science © 2009 W. W. Norton & Company, Inc.
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