First Law of Thermodynamics Conservation of energy Total energy of system plus surroundings constant energy out = energy in – energy stored energy stored (internal energy, E) = energy in – energy out  E = E products – E reactants  H = H products – H reactants (enthalpy)

Second Law of Thermodynamics Thermodynamic spontaneity Process spontaneous only if sum of entropies of system plus surroundings increases Spontaneity = feasibility in particular direction For every process  S system +  S surrounding > 0

Free Energy G = measure of spontaneity; only need parameters of system  G =  H – T  S For every process  G of system must be < 0

Relationship of  G to Equilibrium A ↔ B Equilibrium constant (K eq ) = Free energy lowest at equilibrium Tendency toward equilibrium provides driving force [B] eq [A] eq

Calculating  G A ↔ B aA + bB ↔ cC + dD = -RT ln () + RT ln () [B] eq [A] eq [B] specified [A] specified GG -RT lnK eq + RT ln () [B] specified [A] specified = -RT lnK eq + RT ln () [C] c [D] d [A] a [B] b = GG

Significance of  G for Reaction Feasibility  G < 0: feasible; energy produced by reaction  G > 0: not feasible; energy must be supplied to drive reaction  G = 0: at equilibrium

Standard Free Energy Change  G 0 =  G at 1 M reactants, products; 25ºC = -RT ln K eq = ln K eq or –1.36 log K eq G0G0 = -RT lnK eq + RT ln1

K eq > 1,  G 0 negative K eq < 1,  G 0 positive Standard conditions:  G 0 K eq (kcal/mol) Relationship Between  G 0 &K eq

Determining  G at Given Conditions from  G 0 specified conditions,  G standard conditions,  G 0 Indicates if reaction favorable under: -RT lnK eq + RT ln () [C] c [D] d [A] a [B] b = GG  G 0 + RT ln () [C] c [D] d [A] a [B] b = GG  G ln () [C] c [D] d [A] a [B] b =

Steady State Most reactions in cell far from equilibrium Part of multi-step pathways; uptake of energy Drive toward equilibrium performs work

Driving Unfavorable Reactions  G's of coupled reactions are additive Unfavorable reaction can be driven by coupled favorable reaction A ↔ B + C  G 0 = +4 kcal/mol (endergonic) B ↔ D  G 0 = -8 kcal/mol (exergonic) __________________________________________ A ↔ C + D  G 0 = -4 kcal/mol (exergonic)

ATP Is Universal Energy Carrier Large free energy released from hydrolysis ATP + H 2 O ↔ ADP + P i  G 0 = -7.3 kcal/mol ATP + H 2 O ↔ AMP + PP i  G 0 = kcal/mol

ATP Driven Reactions Hydrolysis often used to drive unfavorable reactions A ↔ B  G 0 = +3 kcal/mol A + ATP + H 2 O ↔ B + ADP + P i  G 0 = -4.3 kcal/mol

ATP-ADP Cycle Fundamental mode of energy exchange

ATP as High Energy Compound Resonance structures of hydrolysis products Large free energy difference between molecules Repulsion by ATP negative charges

Other High Energy Compounds Energy from release of phosphate group

Free Energies of Hydrolysis Standard free energies of hydrolysis of some phosphorylated compounds Compound kcal. /mol Phosphoenolpyruvate ,3-Bisphosphoglycerate-11.8 Creatine phosphate-10.3 ATP (to ADP)-7.3 Glucose 1-phosphate-5.0 Pyrophosphate-4.6 Glucose 6-phosphate-3.3 Glycerol 3-phosphate-2.2