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Bioenergetics

INTER 111: Graduate Biochemistry. Bioenergetics. The change in free energy for a reaction predicts the direction in which it will spontaneously proceed. What do positive, negative, and zero values for D G signify for a chemical reaction?

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Bioenergetics

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  1. INTER 111: Graduate Biochemistry Bioenergetics

  2. The change in free energy for a reaction predicts the direction in which it will spontaneously proceed. What do positive, negative, and zero values for DG signify for a chemical reaction? You should know the relationship of DG between the forward and back reactions and understand the coupling of standard free energy changes (DGo) for multiple reactions. There is a thermodynamic relationship between free energy, enthalpy, and entropy. Bioenergetics: Learning objectives

  3. Bioenergetics • Studies how energy is utilized and transferred in cells. • Is concerned with energy involved in making/breaking of molecular bonds within biological organisms. • includes the study of different cellular processes (cellular respiration, metabolism, growth, and development) that lead to production and utilization of energy in forms such as ATP molecules.

  4. Bioenergetics • It is primarily concerned with the initial and final energy states of a chemical reaction. • The change in free energy between the initial and final states of a reaction allows prediction if the reaction is possible. A B

  5. Relationship between changes in free energy, enthalpy, and entropy free energychange Energy available to do work Heat released or absorbed during a reaction enthalpy change DG = DH – TDS DG DH DS entropy change • Measure of randomness

  6. Changes in free energy of a reaction are defined in two different forms DGrxn = Gproduct – Greactant For any specified [A] and [B] Standard free energy change [A] = 1 M, [B] = 1 M, pH = 7 A B DG A B DGo

  7. A negative DG indicates the reaction is spontaneous as written DGforwardrxn = Gproduct – Greactant = GB – GA A B

  8. A positive DG indicates the reaction is not spontaneous as written DGbackrxn = Gproduct – Greactant = GA – GB A B

  9. The magnitude of DG for the forward and back reactions is equivalent DGforwardrxn= - DGbackrxn A B

  10. At constant temperature and pressure, DG and DGo are related. [B] [A] glucose 6-phosphate fructose 6-phosphate DG= DGo + RT ln A B AB

  11. DGo is predictive only standard conditions [B] [A] glucose 6-phosphate fructose 6-phosphate DG= DGo + RT ln A B DGo = standard free energy change DG = DGo = 1 M A B AB = 1 M standard conditions

  12. DG depends on the concentration of reactants and products [B] [A] glucose 6-phosphate fructose 6-phosphate DG= DGo + RT ln A B Can the reaction proceed in the forward direction, i.e.produce fructose 6-phosphate? DG = DGo = + 0.4 kcal/mol = 0.90 M A B AB nonequilibrium conditions = 0.09 M

  13. DG of a reaction is zero at equilibrium A B nonequilibrium conditions standard conditions equilibrium conditions DG = - 0.96 kcal/mol DG = DGo = + 0.4 kcal/mol DG = 0 kcal/mol = 0.90 M = 1 M = 0.66 M A A A B B B AB = 0.09 M = 1 M = 0.33 M

  14. DG of a reaction is zero at equilibrium [B]eq [A]eq A B equilibrium conditions = Keq=equilibrium constant DG = 0 kcal/mol = 0.66 M A DGo = - RT lnKeq B AB = 0.33 M

  15. DGo values of two consecutive reactions are additive ADP +glucose 6-phosphate ATP + glucose DGo= -4.0 kcal/mol GA glucose 6-phosphate fructose 6-phosphate DGo= +0.4 kcal/mol fructose 6-phosphate DGo= -3.6 kcal/mol glucose GB AB

  16. DG values of consecutive reactions are also additive • Additive property of free energy changes is central to biochemical pathways. • If sum of individual reaction DGs is negative, pathway can proceed as written.

  17. Coupling an energetically favorable process with and an unfavorable one

  18. Reactions are coupled through a common intermediate D D D + + Z A + + D XY BC

  19. Exergonic hydrolysis of ATP is often coupled to endergonic processes ATP ADP + Pi ATP AMP + PPi a g b

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