 “Ability to do work”  Chemical, positional (potential), kinetic (heat), etc. Energy

 Energy is never created or destroyed, only transformed  Entropy (disorder) increases Laws of thermodynamics

 G = free energy   G = change in free energy for some process Free energy glucose + O 2 6 CO 2 + H 2 O oxidation (“burning”)  G = G products – G reactants If G products < G reactants then  G < 0: energy is released exergonic process “spontaneous” process G = H - TS

 G = free energy   G = change in free energy for some process Free energy ADP + PO 4 ATP  G = G products – G reactants If G products > G reactants then  G > 0: energy is required endergonic process “non-spontaneous” process G = H - TS

  G is related to the equilibrium for a reaction  At equilibrium:  Rate of forward and reverse reactions are equal  Amounts of reactants and products don’t change  Amounts of reactants and products may not be equal Free energy k eq = [products] [reactants] at equilibrium If exergonic, k eq > 1 (more products) [CO 2 ] [glucose] > 1 If endergonic, k eq < 1 (more reactants) [ATP] [ADP] < 1

  G does not tell us about the rate of reaction! Free energy For glucose → CO 2, k eq ≈

 Why doesn’t glucose break down on its own?   G doesn’t show the energy path from reactant to product Activation energy

 Is this process endergonic or exergonic? cis to trans transition in retinal

trans-retinal cis-retinal light

Catalysts free energy (G) reaction progress → trans cis GG activation energy

trans-retinal cis-retinal light RPE65

Catalysts free energy (G) reaction progress → trans cis no RPE65 with RPE65 GG activation energy

 Speed up reactions by lowering E A  Not a product or reactant, not changed  Bind molecules transiently Catalysts free energy (G) reaction progress → trans cis no RPE65 with RPE65 GG activation energy

 Proteins  Biological catalysts  Active site Enzymes active site

 Proteins  Biological catalysts  Active site Enzymes trans retinal = substrate

 Active site exactly fits substrate  Doesn’t explain why the enzyme catalyzes the reaction Lock and key model trans retinal = substrate

 Substrate bends to fit active site  Active site flexes to fit substrate  Stabilizes transition state Induced fit model trans retinal

 Which end of a protein do you think this protease cleaves?  Pancreatic enzyme used to break down protein in digestion of foods. Carboxypeptidase A

 Classic support for induced fit.  What is the role of the Zn 2+ ion? Carboxypeptidase A

 What will happen over time? Enzymes and equilibrium 100 grasshoppers

 Will this change the outcome of the experiment? Enzymes and equilibrium 100 grasshoppers

Enzymes and equilibrium 100 no enzyme with enzyme no enzyme with enzyme 100 endergonicexergonic

Enzymes and equilibrium 10 no enzyme with enzyme no enzyme with enzyme 90 endergonicexergonic 90 10

Enzymes do not change:  Equilibrium   G  k eq  How much product is made Enzymes do change:  Rate of reaching equilibrium Enzymes and equilibrium