Microbial Metabolism: Fueling Cell Growth

• Eduard Buchner, a German chemist, showed that crushed yeast cells could convert sugar to ethanol, awarded Nobel Prize in 1907


  1897
• All cells need to accomplish two fundamental tasks: Synthesize new parts and Harvest energy to power reactions
• Metabolism


  Sum of chemical reactions in a cell
• Clear solution of sugar, ammonia, mineral salts, trace elements
• Photosynthetic organisms harvest energy in sunlight to power synthesis of organic compounds from CO2
• Pasteur failed to extract something from inside the cells that would convert sugar
• Louis Pasteur set out to show that yeast were producing the alcohol


  1850s
• Energy in the universe cannot be created or destroyed, but it can be changed from one form to another
• Processes that generate ATP for Chemoorganotrophs

  1. Substrate-level phosphorylation

  2. Oxidative phosphorylation
• Cells use energy to produce ATP


  By adding to adenosine diphosphate (ADP)
• Energy


  The capacity to do work
• Prokaryotes use remarkably diverse energy sources and terminal electron acceptors
• Free energy

  Energy available to do work
• Implications of microbial metabolism

  • Biofuels
  • Food and beverage production
  • Important in laboratory
  • Important models for study
  • Unique pathways are potential drug targets
• Exergonic reactions

  Reactants have more free energy than products (catabolic)
• Alcohol and CO2 are produced in grape juice while yeast cells increase in number
• Forms of energy

  • Potential: stored energy (chemical bonds, rock on hill, water behind dam)
  • Kinetic: energy of motion (moving water)
• Enzymes

  Biological catalysts that speed up conversion of substrate into product by lowering activation energy
• Cells use multiple steps when degrading compounds

  Energy released from exergonic reactions powers endergonic reactions
• Endergonic reactions

  Products have more free energy than reactants (anabolic)
• Electrons removed through series of oxidation-reduction reactions or redox reactions
• Hydrogenation

  Reduction
• Chemical Energy Sources for Prokaryotes

  • Organic, inorganic compounds
  • O2, other molecules
• Redox reactions

  Substance that loses electrons is oxidized, substance that gains electrons is reduced
• Metabolic pathway


  Series of chemical reactions that converts starting compound to an end product
• ATP

  Adenosine triphosphate: energy currency of cell
• Dehydrogenation

  Oxidation
• When electrons move from molecule with low affinity for electrons to one with high affinity, energy is released
• Yeast cells added

  They multiplied, sugar decreased, alcohol level increased
• Chemoorganotrophs obtain energy from organic compounds and depend on activities of photosynthetic organisms or chemolithoautotrophs
• Processes that generate ATP for Photosynthetic organisms

  Photophosphorylation
• Glucose is also the starting point for all cellular components including proteins, lipids, carbohydrates, and nucleic acids
• Glycolysis provides a small amount of ATP
• E. coli can grow in glucose-salts medium
• The Role of Electron Carriers

  1. Energy harvested in stepwise process

  2. Electrons initially transferred to electron carriers

  3. Can be considered hydrogen carriers

  4. Ultimately drive synthesis of ATP or biosynthesis
• More energy is released when the difference in electronegativity (affinity for electrons) is greater
• Electron Carriers

  • Nicotinamide adenine dinucleotide (carries 2 electrons and 1 proton)
  • Flavin adenine dinucleotide (carries 2 electrons and 2 protons; that is, 2 hydrogen atoms)
  • Nicotinamide adenine dinucleotide phosphate (carries 2 electrons and 1 proton)
• Fermentation recycles electron carriers in a cell that cannot respire so that it can continue to make ATP
• Glucose is the energy source for E. coli
• O2 is a terminal electron acceptor in aerobic respiration