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PART II: Energetics and Enzymes

PART II: Energetics and Enzymes. Free energy of formation (G 0 f ) for compounds. Energy needed for the formation of a compound Used to calculate ΔG 0 ’ of a reaction If the formation of a compound is exergonic, then Gº f is - If the formation of a compound is endergonic, then Gº f is +.

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PART II: Energetics and Enzymes

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  1. PART II: Energetics and Enzymes

  2. Free energy of formation (G0f) for compounds • Energy needed for the formation of a compound • Used to calculate ΔG0’ of a reaction • If the formation of a compound is exergonic, then Gºf is - • If the formation of a compound is endergonic, then Gºf is +

  3. Free energy of formation

  4. Predicting reactions • ΔGº’ of A+BC+D Gºf [products]- Gºf [reactants] • ΔGº’ of the reaction H2 + ½ O2H2O ΔGº’= Gºf [H2O]- (Gºf [H2] + Gºf ½ O2) (- 237.2) – (0 + ½ 0) = - 237.2 KJ/mol • Is this endergonic or exergonic?

  5. What is the ΔGº’ of the following reactions? • CH4 + ½ O2CH3OH • H2S + 4H20 + 8Fe+3  8Fe+2 + 10H+ + SO4-2 • (at pH7)

  6. Prosthetic groups Bound very tightly to enzymes Example: heme group in cytochromes Enzymes associate with other molecules • Coenzymes • Bound loosely to the enzyme • Examples: vitamins

  7. PART III Oxidation-Reduction and Energy-Rich Compounds

  8. Example • H2 + fumarate2-succinate2- • Oxidation of Hydrogen: (electron donor) • H22 e- +2 H+ • Reduction of fumarate: (electron acceptor) • fumarate2- + 2 e- +2 H+  succinate2- • 2 half reactions – are linked • 1 reaction = oxidation and electron donor • 1 reaction = reduction and electron acceptor

  9. Reduction potential, E0' • The tendency of a compound to accept or release electrons • Vertical tower of reduction potentials • The most negative E0's on the top • Greatest electron donor potential • Those with the most positive E0's on the bottom • Greatest electron acceptor • Donors can pass electrons to acceptors below them on tower only • As electrons are passed from a donor, energy is released  E0‘ = G0'

  10. Electron tower

  11. Questions? • Which compound on the tower has the greatest ability to donate electrons? • Which compound on the tower has the greatest ability to accept electrons? • Can cytochrome B donate electrons to iron (Fe+3)? • Can ubiquinone accept electrons from iron Fe+3?

  12. Does anyone know in the electron transport chain, what compound has the greatest ability to accept electrons and what compound has the greatest ability to donate electrons?

  13. Reduction potentials • ΔEo’= difference in potential • The larger the ΔEo’ during a redox reaction, the greater the energy released • Or the farther the electrons fall down the tower the more potential energy produced

  14. Redox reactions in metabolism • NAD+/NADH: catabolic reactions • NADP+/NADPH: anabolic reactions • NAD+/NADH, E0’ = -0.32 • Is NADH a good electron acceptor or electron donor?

  15. In metabolism there are different electron carriers • NADH • FADH2 • NADPH They carry hydride ions = 2 hydrogen + 2 electrons Acetyl CoA – carries an activated sulfhydryl group ATP carries an activated phosphate group

  16. Questions • Is NAD+ in the oxidized or reduced form? • Is FADH2 in the oxidized or reduced form? • If a series of reactions is about to take place, would you say that NADH is going to be oxidized or reduced? What about FAD+? • Which of the following compounds would pick up electrons – NAD+, NADH, FAD+ or FADH2?

  17. NADH is formed during glycolysis NAD+ is regenerated during fermentation or the electron transport chain Role of NAD+/NADH in metaobolism

  18. Carrier molecules involved in different biochemical reactions Carrier molecule Group carried • ATP phosphoryl • NADH and NADPH electrons (and hydrogen) • FADH2 electrons (and hydrogen) • Coenzyme A acetyl

  19. High Energy Bonds

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