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BCH110A-LEC2_Bioenergetics_2011

# BCH110A-LEC2_Bioenergetics_2011 - BIOC 110A Fall 2011...

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BIOC 110A, Fall 2011 LEC 2, Biological Thermodynamics (Dr. Ziegler © 2011) 1 Lecture 2 Biological Thermodynamics (Bioenergetics) Reading : Lehninger Principles , 5th ed.: chapter 1, pp. 20-27; chapter 13, pp. 489-511 Thermodynamics calculations: Worked examples 13-1 (p. 492) and 13-2 (p. 503), which will not be gone over in class ; practice problems (chapter 13, pp. 522-523) #2-15. Abbreviated solutions are at end of textbook; detailed solutions are in the back The Absolute, Ultimate Guide to Lehninger…, 5th edition”, on reserve in Science Library BIOCHEMISTRY 110A Fall 2011 M. Ziegler Key Concepts Transformation of energy and matter from surroundings --> complex, orderly structures Bioenergetics : the quantitative study of energy transformations in biological systems -- these concepts are the underpinnings for all of biochemistry and molecular biology Change in Gibbs free energy ( Δ G) for a reaction quantitates the energy available to do useful work is related to the change in enthalpy and the change in entropy: Δ G = Δ H - T Δ S Actual free energy change ( Δ G) depends on 2 parameters: 1. standard free energy change for that reaction ( Δ G o ) (and thus to K eq , deFning where equilibrium for this reaction lies) , and 2. actual mass action ratio , reFecting actual starting conditions , the actual concentrations of reactants and products Δ G (actual) = Δ G o + RTln{actual mass action ratio} Standard free energy change for a reaction ( Δ G o ): the change in free energy for going from STANDARD CONDITIONS TO EQUILIBRIUM . reFects K eq : Δ G o = – RTlnK eq

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BIOC 110A, Fall 2011 LEC 2, Biological Thermodynamics (Dr. Ziegler © 2011) 2 Key Concepts, continued SIGN of Δ G tells us DIRECTION the reaction would have to go to reach equilibrium (the "spontaneous" direction). Reactions ALWAYS proceed in direction to go toward equilibrium . Negative value for Δ G means equilibrium lies to right (reaction will go as written, left to right). Positive value for Δ G means equilibrium lies to left (reaction will go right to left). Δ G gives NO information about RATE at which reaction will go. Free energy changes are ADDITIVE . For coupled or sequential reactions , overall free energy change for process is SUM of Δ Gs for component reactions or processes . Additivity of free energy changes permits FREE ENERGY COUPLING : an exergonic reaction can "drive" an endergonic reaction (sum of component Δ Gs is negative) if the reactions can be coupled. Key Concepts, continued Compounds with high group transfer potentials (large negative free energies of hydrolysis) can be used to “drive” endergonic processes in cells (free energy coupling). Enzymes are
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BCH110A-LEC2_Bioenergetics_2011 - BIOC 110A Fall 2011...

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