Chp.14 Principles of BioenergeticsMetabolism = the sum of all chemicalreactions that take placein a cell or organism.Bioenergetics = the quantitative study ofthe energy transductions that occur inin living cells and the nature and functionof the chemical processes underlying thesetransductions.4 x 10 11metric tons of carbonare turned over in thebiosphere each year.Catabolic pathways generally converge. Anabolic pathways divergeSome pathways are cyclic.AMetabolic“Map”Acetyl-CoAplays centralroleVoet & VoetFig. 15-1Acetyl-Coenzyme AFig 3-6 Page 57Oxidation of glucose24 electronsGlucose + 6O26CO2+ 6H2O∆G’o = -686 kcal/moleGlycolysis -> Citric Acid Cycle -> Oxidative PhosphorylationA fraction of this free energy will beharvested as chemical energy in theform of ATPBiological Systems Obey the PhysicalLaws of Thermodynamics∆G = ∆H - T∆S∆H = ∆U + P∆VG = Gibbs Free EnergyH = EnthalpyS = EntropyU = Internal EnergyFirst Law of Thermodydamics -The Principle of Conservation of EnergyFor any physical or chemical change, the total amount ofenergy in the universe remains constant; energy may change form as it is transported from one region to another, but itcannot be created or destroyed.Living systems can couple energy requiring reactions tothose which are spontaneous (exergonic)A chemical example of reaction couplingThe Second Law of ThermodynamicsIn all natural processes, the entropy of the universeincreases.The oxidation of glucose results in a significant increasein entropy.Free Energy Calculations:aA + bB cC + dD , ∆Grxnenzyme∆G = ∆G'o + RT ln[C] [D] [A] [B]cdab∆G < 0, product formation is favored∆G = 0, reaction at equilibrium∆G > 0, substrate formation favoredcdab∆G'o = -RT ln eq eqeqeq[C] [D] [A] [B]At equilibrium,If all [i] = 1 M,∆G = ∆G'oAdenosine triphosphate (ATP)Why is ATP a “high-energy” compound ?Garrett & GrishamFig. 3.8ATP in water is not readily convertedto ADP, but needs enzymes to mediate hydrolysis.ATP + H2O Slow reactionADP + HPO42-ATP iskineticallyverystableATP the universal energy carrier.It releases a significant amount of free energy upon hydrolysis.But not too much so it can be a conduit between “high energy”phosphate donors and low energy acceptors.Why are the hydrolysis products (ADP+Pi) more stable than the reactants (ATP)?(1) More resonance forms per phosphate in hydrolysis productsATPADP Pi(2) Charge separation in products(3) Better solvation of productsCreatine.E = E' + lnoRT [e- acceptor] nF [ e- donor]E = reduction potential F = Faraday's constant n = number electrons∆G =
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