INTER 111: Graduate Biochemistry

 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  G signify for a chemical reaction?  You should know the relationship of  G between the forward and back reactions and understand the coupling of standard free energy changes (  G o ) for multiple reactions.  There is a thermodynamic relationship between free energy, enthalpy, and entropy.

 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.

 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

FREE ENERGY CHANGE Energy available to do work Heat released or absorbed during a reaction ENTHALPY CHANGE ENTROPY CHANGE Measure of randomness HH GG SS

For any specified [A] and [B] Standard free energy change [A] = 1 M, [B] = 1 M, pH = 7  G rxn = G product – G reactant  G rxn = G product – G reactant A  B GG GG GoGo GoGo

 G forward rxn = G product – G reactant = G B – G A  G forward rxn = G product – G reactant = G B – G A A  B

 G back rxn = G product – G reactant = G A – G B  G back rxn = G product – G reactant = G A – G B

 G forward rxn = -  G back rxn A  B

 G =  G o + RT ln [B] [A] [B] [A] A  B glucose 6-phosphate fructose 6-phosphate A  B

 G =  G o + RT ln [B] [A] [B] [A] A  B glucose 6-phosphate fructose 6-phosphate A  B standard conditions A B = 1 M  G =  G o  G o = standard free energy change

 G =  G o + RT ln [B] [A] [B] [A] A  B glucose 6-phosphate fructose 6-phosphate A  B  G =  G o = kcal/mol A B = 0.90 M = 0.09 M Can the reaction proceed in the forward direction, i.e. produce fructose 6-phosphate? nonequilibrium conditions

nonequilibrium conditions standard conditions A B = 0.90 M = 0.09 M A B = 1 M  G = kcal/mol  G =  G o = kcal/mol equilibrium conditions A B = 0.66 M = 0.33 M  G = 0 kcal/mol A  B

equilibrium conditions A B = 0.66 M = 0.33 M  G = 0 kcal/mol A  B = K eq = equilibrium constant [B] eq [A] eq [B] eq [A] eq  G o = - RT ln K eq

 G o =  4.0 kcal/mol glucose 6-phosphate fructose 6-phosphate A  B  G o = +0.4 kcal/mol  G o =  3.6 kcal/mol G  A G  B ATP + glucose ADP + glucose 6-phosphate glucose fructose 6-phosphate

 Additive property of free energy changes is central to biochemical pathways.  If sum of individual reaction  Gs is negative, pathway can proceed as written.

X  Y + ZD + B  C +D+D A + D D

   ATP ADP + P i ATP AMP + PP i