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Microbial Metabolism

Microbial Metabolism. Metabolic Reactions Enzymology Catabolism Litho/Phototrophy Anabolism. Chemoorganoheterotroph Metabolism Overview:. Reduction; e - gain from donor. Oxidation; e - loss to acceptor. Laws of Thermodynamics.

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Microbial Metabolism

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  1. Microbial Metabolism Metabolic Reactions Enzymology Catabolism Litho/Phototrophy Anabolism

  2. Chemoorganoheterotroph Metabolism Overview: Reduction; e- gain from donor Oxidation; e- loss to acceptor

  3. Laws of Thermodynamics • First: energy is neither created not destroyed; it simply changes state. • E.g. light to chemical & heat; • E.g. chemical to work and heat • Second: the order of a system always decreases; it becomes more random (i.e. entropy increases). • E.g. gases expand • E.g. concentration gradients • Free Energy of Chemical Reactions: • Enthalpy (H) = reaction heat • Entropy (S) = degree of randomness; disorderliness • Change in Free Energy during a chemical reaction: (ΔG = ΔH - T·ΔS)

  4. Standard Free Energy Change (ΔGo’) and Reaction Equilibrium • Negative ΔGo’ = spontaneous (exergonic) reaction. • Negative ΔH; heat release during reaction • Positive ΔS; increase in randomness • Reaction equilibrium shifts to product. • Positive ΔGo’ = endergonic reaction. • Positive ΔH = heat absorbed during reaction • Negative ΔS = reaction becomes more ordered • Reaction equilibrium shifts to reactants • Requires coupling with strong exergonic reaction to shift reaction equilibrium to the product. The role of ATP! • ΔGo’ = 0 • Direction of reaction is from high to low concentrations. • Reversible reactions.

  5. Oxidation-Reduction (Redox) ΔEo’ = Change in standard reduction potential (Eo’)ΔE’o = (E’o acceptor - E’o donor)ΔGo’ = -nF·ΔE’o D + e-→ D- A+ + e-→ A Coupled ½ reactions: + A+ = acceptor; More positive E’o A reduced D- = donor; More negative E’o D oxidized

  6. Spontaneous (-ΔGo’ or +ΔE’o): ½ O2 + NADH → H2O + NAD+ ΔE’o = 0.815V – (-0.42V) = 1.235V Endergonic (+ΔGo’ or -ΔE’o): H2O+ NADP+→ ½ O2 + NADPH ΔE’o = -0.42V – 0.815V = -1.235V BetterDonors Better Acceptors

  7. Electron Carriers: NADH reduced • Electrons like to flow from negative to positive E’o; releasing energy in the transfer. • Electron Carrier Functions: • Control the release of energy for work. • Supply “reducing power” in anabolic reaction. • Electron Carrier Types: • NADH / NADPH (free) • FAD / FMN (free or as flavoprotein) • Coenzyme Q (= Ubiquinone) (“dissolved” in lipid membranes) • Cytochromes (Iron-porphyrin ring + protein) • Non-heme Iron Protein (e.g. ferredoxin FAD oxidized

  8. Electron Carriers: Ubiquinone (CoQ) Heme (iron-porphyrin ring)

  9. A cell must get fuel to do work. • Fueling reactions: • Control electron flow (donors to acceptors) • Electron carriers • Fueling or work (reductive biosynthesis) • Capture energy in a standard form (ATP) • Substrate level phosphorylation • Electron Transport System (ETS) involvement • Photophosphorylation • Oxidative phosphorylation • Work (mechanical, transport, biosynthesis) • Enzymes are needed to catalyze and control the rate of both fueling and work reaction.

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