Chapter 13 - Chapter 13 Principles of Bioenergetics Read Intro to part II on your own 13.1 Bioenergetics and Thermodynamics A Biological Transformations

Chapter 13 - Chapter 13 Principles of Bioenergetics Read...

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Chapter 13 Principles of Bioenergetics Read Intro to part II on your own 13.1 Bioenergetics and Thermodynamics A. Biological Transformations obey Laws of thermodynamics 1 law, - in any physical or chemical change total amount of E in universe st is constant (E not created or destroyed) 2nd law entropy of universe (S) is always increasing Background - what is entropy use 3 quantities to describe the energy of chemical processes Enthalpy ( Ä H j/mol) heat content of the system, is negative if heat released Entropy ( Ä S J/mol @ K) randomness of the system, is positive if gets more random Free Energy ( Ä G j/mol) energy available for doing work is - for spontaneous reactions Review of Gen Chem terms Internal Energy -E -Sum of kinetic and potential energy of all particles in a system Enthalpy -H- heat content of a reaction Entropy -S- a measurement of randomness in a system Gibbs Free Energy -G- Amount of energy available to do work In biological systems, P, T constant Ä G = Ä H -T Ä S Since Ä H is a measure of heat released to surrounding you can think of as randomness of surroundings Ä S is randomness of system itself So Ä G is a measure of overall randomness of universe and as long as that is negative, the randomness of universe has increased and the reaction can be spontaneous B. Cells Require Sources of Free Energy Most cells are in isothermal and isobaric environment (Constant T and P) Since constant T, cannot use heat flow as energy source So Gibb Free energy is only form of energy available
2 eq C. Free energy related to K aA + bB 6 cC + dD eq K = [C] [D] / [A] [B] c d a b eq Ä G= -RT lnK If not at equilibrium will try to move in that direction Ä G is a measure of how far from equilibrium you are when everything is o []=1M T=298 P=1atm [gas]=1 atm Not a great def for biochemists 1M H = pH 0 + 2 [H O]=55.5M and essentially a constant 2 Ä G ’ used in Biochem for pH=7, [H O]=55.5M and essentially a constant o eq Ä G ’ = -RT lnK’ o eq Note 1: - Ä G ’, K >1, reaction go toward products o eq + Ä G ’, K <1, reaction go toward reactants o eq can use to convert from Ä G to K Note 2: This book state that [Mg ] is also treated as a constant. I have 2+ not seen that before Problem 2(b) from end of chapter Calculate Ä G for the reaction: o Dihydroxyacetone phosphate W glyceraldehyde 3-phosphate eq Given that the K’ for the reaction is 0.0475 eq Ä G ’= -RT ln K’ o =8.3145 J/K·mol ×298K ×ln(.0475) = +7550 J/mol = 7.55 kJ/mol D. Actual free-energy changes depend on reactant and product concentrations Ä G ’ the energy change when [] start at 1M o Ä G the energy change that occurs for a reaction under a particular set of conditions Note these are different. Lots of tables around that tabulate Ä G ’ for various biochemical reactions o
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