Microbial Metabolism - Download as PowerPoint by 3KYoLCe

VIEWS: 117 PAGES: 22

									        Microbial Metabolism
• Overview of metabolism (you should know about
  TCA cycle, Embden-Meyerhof pathway-
  glycolysis, Proton motive force etc.)
• Overview of nutrition
• Culture media
• Energetics
• Enzyme catalysis
• Oxidation and reduction
• Electron carriers
• Energy conservation
Metabolism
     Energy classes of microbes
• microbes need three things to grow:
   – Energy source
   – Nutrients (C)
   – Suitable environmental conditions
• Energy source
   – Phototroph (light)
   – Chemotroph (chemicals)
      • Chemoorganotroph (organic chemicals)
      • Chemolithoautotroph (inorganic chemicals)
               Macronutrients
•   Carbon (CO2 or organic compounds)
•   Hydrogen (H2O or organic compounds)
•   Oxygen (H2O or organic compounds)
•   Nitrogen (NH3, NO3-, organic N-compounds)
•   Phosphorus (PO43-)
•   Sulfur (H2S, SO42-, organic compounds)
•   Potassium (K+)
•   Magnesium (Mg2+, salts)
•   Sodium (Na+)
•   Calcium (Ca2+, salts)
•   Iron (Fe3+, Fe2+, or salts)
           Iron as a nutrient
• Needed for aerobic metabolism
  (cytochromes, iron-sulfur proteins)
• Insoluble under aerobic conditions
  – Fe(OH)3, FeOOH
  – Solubilized by siderophores
Siderophore
Iron uptake
    Micronutrients and growth
             factors
• Micronutrients: Metals and metalloids
  – Generally not necessary to add to medium
  – Deficiencies can arise when medium
    constituents are very pure
• Growth factors: organic requirements
  – Vitamins, amino acids, purines, pyrimidines,
    acetate
             Culture media
• Defined: all chemicals are ostensibly known
• Complex (undefined): contains substances
  with unknown chemistries, such as
  peptones, yeast extract, lake water, soil
  extract, etc.
                Energetics
• Gibbs Free-Energy (G)
• Reaction has a free-energy change
  – Negative: exergonic
  – Positive: endergonic
  – Zero: equilibrium
• Standard concentrations—tables of ΔGf°’
            Redox Reactions
• Reactions can be written as half-reactions
  – Oxidation: removal of electrons
     • S → P + e- or            H2 → 2H+ + 2e-
  – Reduction: addition of electrons
     • S + e- → P   or   O2 + 4H+ + 4e- → 2H2O
• Energetics of redox reactions can be
  considered as electrical potentials (see
  electron tower)
Calculation of reaction energetics
• First, must write balanced equation
  – E.g., 2H2 + O2 → 2H2O
• Calculation of ΔG°’ for a reaction
  – ΔG°’ = ΔGf°’products - ΔGf°’reactants
  – ΔG°’ = 2 x (-237.2 kJ/mol) – (2 x 0 + 0)
• Calculation of ΔG for a reaction
  – ΔG = ΔG°’ + RT x ln(k)
              Electron Tower
• A redox reaction needs a reducing and oxidizing
  half-reaction
• Reactions with stronger tendency to give up
  electrons are higher (more negative) on the tower
• To determine which direction the reactions go, see
  which is ―higher‖ on the electron tower
• Note the position of important electron carriers
  (NAD, FAD, cytochrome a) and external electron
  donors/acceptors (H2, organic compounds, O2)
Chemical kinetics and enzyme
          catalysis
Electron carriers: NAD
NAD+   as co-enzyme
NADH as co-enzyme
     NAD as electron carrier
• NAD+ + ED → EDox + NADH
• NADH + EA → EAred + NAD+
• Overall reaction:
  – ED +EA → EDox + EAred
      High-energy compounds
• ATP is the energy currency of the cell
  – High energy released when phosphate is
    hydrolyzed (ATP, ADP, AMP)
• Acetyl phosphate
• Acetyl coenzyme A
• Phospho-enol pyruvate
 Modes of E Conservation-ATP
• Fermentation: in which redox reaction ocurs
  WITHOUT a terminal electron acceptor
  (couple oxiation with subsequent reduction of an organic
  product generated from initial substrate)
• Respiration: in which O2 or another oxidant
  serves as an electron acceptor
  MORE Modes of E generation
• Anaerobic Respiration
• Chemolitho(auto)trophy
• Photo(auto)trophy

• WHAT DO ALL THESE HAVE IN
  COMMON?
Overview of fermentation

								
To top