Metabolic Reactions Enzymology Catabolism Litho/Phototrophy Anabolism Microbial Metabolism

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

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)

Negative ΔG o ’ = spontaneous (exergonic) reaction. –Negative ΔH; heat release during reaction –Positive ΔS; increase in randomness –Reaction equilibrium shifts to product. Positive ΔG o ’ = 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! ΔG o ’ = 0 –Direction of reaction is from high to low concentrations. –Reversible reactions. Standard Free Energy Change (ΔG o ’) and Reaction Equilibrium

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

Spontaneous (-ΔG o ’ or +ΔE’ o ): ½ O 2 + NADH → H 2 O + NAD + ΔE’ o = 0.815V – (-0.42V) = 1.235V Better Donors Better Acceptors Endergonic (+ΔG o ’ or -ΔE’ o ): H 2 O + NADP + → ½ O 2 + NADPH ΔE’ o = -0.42V – 0.815V = V

Electron Carriers: 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 NADH reduced FAD oxidized

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

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.