S 2007 BIOC 3406

1. S 2007 BIOC 3406 01-18-07

2. Principles of Bioenergetics

3. Management of energy is a characteristic of living systems • ♫♫Stayin’ Alive… • Growth • Reproduction

4. Life uses energy to… • Synthesize the molecules of life • Produce • Motion • Heat • Light • Create gradients (establish potential fields) • Concentration • Chemical • Hydrogen ion • Electrical potential

5. Life obtains energy • From environmental heat? • From light? • - From chemical fuel • Respiration

6. Thermodynamics • Energy – “The capacity to do work” q, heat; disorganized energy. Can only do work by passing from high to low temperature w, work; organized energy. Can be pressure-volume work electrical work concentration work

7. “Free” energy • Essentially from the sun • Spectrum of very hot body • Energy density of cool body • Direct from sun • Photosynthetic cells • Heterotrophic cells

8. G, “Free” energy • Process converts reagents A into products B • G is the energy difference in the products B in their standard states and the reagents A in their standard states

9. Thermodynamics • E = q + w E is the change in internal energy (kinetic + potential energy) • H = E + PV ( at constant P) H is the Enthalpy; the “heat of reaction” at constant T and P • G = H - TS (constant T, P G is the change in Gibbs Free energy

10. Systems • Isolated • No interaction with the rest of the universe • Closed • Exchanges energy with the rest of the universe • Open • Exchanges matter as well as energy with the rest of the universe

11. Processes A  B In a real process, S is positive (2nd Law) (S of universe) G’s sign gives the character of the process G = 0 A, B already in equilibrium G > 0 A increases, B decreases G < 0 B increases, A decreases

12. Processes • If A↔B, at equil, then if start with A ↔ B, B will↑, A will↓ • If A↔ B, at equil, then if start with A ↔ B, A will↑, B will↓

13. Equilibrium • When A and B are in the same medium, there is continuous interconversion A  B and B  A If forward and backward rates are equal, system is in equilibrium Ratio of backward and forward rates = K, the equilibrium constant K is also numerically equal to the ratio of the products to the reagents at equilibrium

14. Q “Mass Action Ratio” • For any mixture of A and B, Q is the ratio of the products and reactants at any instant • If product of product concentrations > product of reactant concentrations, Q < 1 • If product of reactant concentrations > product of product concentrations, Q > 1 • If product of product concentrations = product of reactant concentrations, Q = 1

15. Meaning of Superscripts • “°” • Standard state: Reagents, products at 1M, pH 0 (H+ at 1M) (If acid-base reaction) • “’” • Biochemical standard state: pH 7, Mg2+ ~1 mM, aqueous solvent

16. G, G’° • G – A driving force • For conditions A, B (actual concentrations) • G’° – A driving force • For conditions A’°, B’°

17. G, G’° • G° = - RTln K =-RTln (std forward rate)/(std backward rate) • G = -RTln Q =-RTln (actual forward rate)/(actual backward rate)

18. Problems • p 518, 2-5

19. K 270 890 Glucose 6-phosphate + H2O  glucose + Pi ATP + glucose  glucose 6-phosphate G = G1 + G2 = - RTln K = - RTln K1 - RTln K2 = - RT(ln K1 + ln K2) = - RT (ln K1K2) = - RTln K

20. Phosphoryl Group Transfer • Hydrolysis of anhydrides, esters creates an acid or other active compound, drives equilibrium to the right • Hydrolysis of ATP • -30.5 kJ/mol • PEP +H2O  pyruvate • -61.9 kJ/mol! • 1,3-bisphosphoglycerate  Pi + 3-PG • -49.3 kJ/mol • Acetyl coenzyme A + H2O  CoASH • -31.4 kJ/mol