4-1 Chapter 4: Outline Thermodynamics First Law Second Law Free Energy Standard free energy changes Coupled reactions Hydrophobic effect (revisited) Role of ATP

4-2 Bioenergetics Each formation or breakdown of a biomolelcule involves an associated energy change. Thermodynamics is the field of chemistry that studies these energy changes. The goal of thermodynamics is to predict whether a reaction will occur spontaneously which, in a chemical sense, means it will continue without energy input once started.

Thermodynamics The heat and energy transformations studied by thermodynamics take place in a system (defined by the investigator) connected to the surroundings (the rest of the universe). Closed system: energy exchanged between system and surroundings. Open system-matter and energy exchanged between system and surroundings.

4-4 First Law-1 Energy is neither created nor destroyed. or  E = q+w  E is the change in the internal energy and is a state function, i. e. independent of path. q is heat and is not a state function. w is work and is not a state function.

4-5 First Law-2 Biochemical systems function at constant pressure, volume, and temperature. H(enthalpy) = E + PV or  H =  E and  H = q (heat flow) The change in enthalpy for a reaction is calculated using the equation  H reactants =  H products –  H reactants -  H is exothermic +  H is endothermic

4-6 First Law-3 Given the equation and the  H f values, calculate the  H for the reaction. 6 CO H 2 O  C 6 H 12 O O 2kJ/mol C 6 H 12 O CO O 2 0 H 2 O [1* *0]-[6* *-68.4)]=+670 kJ Prod - Reactants

4-7 Second Law With a spontaneous reaction, the entropy of the universe increases.  S univ =  S system +  s surroundings In irreversible processes, entropy is a driving force.

Gibb’s Free Energy Gibb’s free energy change (  G) is the most useful thermodynamic function for predicting reaction spontaneity. The two other thermodynamic quantities that contribute to the value for  G:  H=enthalpy change (energy change measured at constant pressure)  S=entropy change (related to the state of disorder in a system)

4-9 Gibb’s Free Energy: 2 The three thermodynamic quantities are related by the following equation:  G =  H -T  S sys For biochemists,  G is usually measured at 25 o C, one atm for a gas, and at a concentration of 1 M for solutes except hydronium ion which is at pH 7. These conditions specify a standard  G represented as  G o ’.

4-10 Gibb’s Free Energy: 3 In a spontaneous reaction: free energy decreases,  G is negative energy is released by the reaction reaction is said to be exergonic In a nonspontaneous reaction: free energy increases,  G is positive energy is absorbed by the reaction reaction is said to be endergonic

4-11 Examples,  G values (From standard tables)  G o ’,kJ/mol (kcal/mol) Exergonic reaction: ATP + H 2 O  ADP + Pi-30.5 (-7.3) Endergonic reaction: glucose-6-phosphate to fructose-6-phosphate+ 1.7 (+0.4)

4-12  G o and K eq For the reaction aA + bB = cC + dD  G =  G o + RT ln [C] c [D] d [A] a [B] b At equilibrium,  G = 0  G o = - RT ln K eq

4-13 Coupled Reactions Frequently in biochemistry two reactions are “coupled” or run as a pair. One reaction is endergonic but the second reaction is exergonic. The sum of the reactions (and the  G changes) is overall exergonic and consequently the reaction pair is overall spontaneous. This is shown on the next slide.

4-14 Coupled Reactions: 2  G o ’(kcal/mol) 1.glucose-6-P  fructose-6-P fructose-6-P + ATP  fructose-1,6-bisP + ADP glucose-6-P + ATP  fructose-1,6-bisP + ADP The overall reaction 3 (sum of 1+2) is exergonic. Sum of  G o ’ 1 +  G o ’ 2 is  G o ’ 3 or –3.0 kcal/mol. Overall reaction is spontaneous

Bioenergetics and ATP Hydrolysis of adenosine triphosphate (ATP) provides the free energy to drive most endergonic reactions. ADP + P i = -7.3 kcal/mol AMP + PP i = -7.7 kcal/mol PP i  2 P i = -8 kcal/mol

4-16 ATP Drives several processes: Biosynthesis of biomolecules Active transport across membranes Mechanical work (e. g. muscle contraction) Can carry phosphoryl groups from higer- energy compounds to lower-energy compounds.

4-17 kJ/mol kcal/mol Glucose-6-P Fructose-6-P ATP  AMP + PP i ATP  ADP + P i P-creatine Glycerate-1,3-bP Phosphoenolpyruvate  G o’ for ROPO H 2 O