CHAPTER 3: ENERGY, CATALYSIS AND BIOSYNTHESISBasic Thermodynamics-First Law of Thermodynamics: -Energy cannot be created or destroyed, but it can be converted from one form to another-Conversion between different forms of energy:-Potential  kinetic  heat-Chemical-bond  kinetic  heat-Chemical-bond  electric  kinetic-Electromagnetic  electron  heat-Second Law of Thermodynamics: -Energy spontaneously tends to disperse = ENTROPY -The Second Law states that ENTROPY increases whenever anything happens. -The text defines entropy as disorder, but more accurately, it is the dispersal of energy.-How do cells manage to create and maintain order despite ever increasing entropy?-Cells use a tremendous amount of energy to create and maintain order. - The Second Law still holds true because entropy in the surroundings increases, largely due to the release of heat (also energy!)-Where do cells get the energy required to create and maintain order?-The environment-Light (electromagnetic energy) -Food (chemical bond energy)- Cells obtain energy from the oxidation of organic molecules (partial harvest of bond energies) -Glucose + 6O2  6CO2 + 6H2O -In the presence of oxygen: -The most energetically stable form of C is CO2 -The most energetically stable form of H is H2OOxidation and Reduction-Generally applies to the gain or loss of electrons -Loss of electron = oxidation -Gain of electron = reduction-Electron transfer often also involves a proton -A + e- + H+  AH -Dehydrogenation = oxidation -Hydrogenation = reduction-Reduced organic compounds yield more energy (electrons) for chemical work: -fats > sugarsFree Energy, G-The molecules of a living cell possess energy because of their vibrations, rotations, and movement through space, and because of the energy that is stored in the bonds between individual atoms -The free energy, G (in kcal/mole), measures the energy of a molecule that could in principle be used to do useful work at constant temperature, as in a living cell -Energy can also be expressed in joules (1 cal = 4.184 joules)-What determines whether a chemical reaction can occur? -Change in free energy  Delta G (change from one molecular state to another)-Energetically favorable reactions have a negative Delta G-Chemical reactions within the cell do not occur in a closed system and are reversible. -Thus, Delta G depends on the energy stored in chemical bonds (Delta Gº) and also on the concentration of the molecules in a reaction.-Delta G = Delta G°+ RT ln [products]/[reactants]-Delta Gº, the standard free energy, reflects the intrinsic energy stored in bonds and is defined under standard conditions: -25ºC (298ºK) -1 atm pressure -All reactants and products at 1 M concentration -pH 7- RT = gas constant × absolute temp = 0.616 @ 37ºC-Energetically favorable reactions have a negative Delta G-ATP  ADP + Pi (Delta Gº/-7.3 kcal/mole)-glucose + fructose  sucrose (+5.5 kcal/mole)-Energetically unfavorable reactions (positive DG) are those that create order.-Effect of concentrations on Delta G (Example)glyceraldehyde 3-P (G3P)  dihydroxyacetone-P (DHAP)Delta Gº = -1.8 kcal/mol Delta G = Delta Gº + RT ln [products]/[reactants] Delta G = Delta Gº + RT ln [DHAP]/[G3P], so Delta G = -1.8 kcal/mol + 0.616 ln [DHAP]/[G3P]If [G3P] = 0.001 M and [DHAP] = 0.1 M : Delta G = -1.8 kcal/mol + 0.616 ln [0.1]/[0.001] Delta G = -1.8 kcal/mol + 2.8 kcal/mol = +1.0 kcal/mol*The “favored” direction of the reaction is reversed-Delta G at Equilibrium-There is no work at equilibrium so Delta G = 0 -0 = Delta G = Delta Gº + RT ln Keq-The effect of concentration is just sufficient to balance Delta Gº.-At equilibrium the forward and reverse RATES for a reaction are equal, but not necessarily the concentrations of the reactants and products.-Relationship between Delta Gº and Keq-0 = Delta G = Delta Gº + RT ln Keq -Delta Gº = -RT ln Keq = -0.616 ln Keq-The greater the value for Keq, the more negative Delta Gº -Delta Gº and Keq values can be used to predict: 1. Ratio of reactants to products at equilibrium 2. Direction of reactionsPredicting Reactions-To predict the outcomes of a reaction (as in which direction will it proceed and when will it stop), we must measure its standard free-energy change (Delta Gº)-This quantity represents the gain or loss of free energy as one mole of reactant is converted to one mole of product under “standard conditions”-All molecules present at a concentration of 1 M and pH 7.0-Delta Gº for some reactions-glucose-1-P  glucose-6-P = -1.7 kcal/mole-sucrose  glucose + fructose = -5.5 kcal/mole-ATP  ADP + Pi = -7.3 kcal/mole-glucose + 6O2  6CO2 + 6H2O = -686 kcal/mole-Coupled Reactions-The energetically unfavorable reaction is driven by the energetically favorable reaction because the free-energy change for the pair of coupled reactions is less than zero-Types of coupled reactions:-Sequential “siphon”-Activated carrierBiosynthesis and Activated Carrier Molecules-Activated carriers store energy in the form of a transferable chemical group or as high-energy electrons. -ATP, NADH and NADPH-Coupling to ATP Hydrolysis Consider a generalized condensation reactionA - OH + B – H  A – B +H2OThis reaction is energetically unstableCoupling to ATP hydrolysis occurs in two steps ATP  ADP1. A – OH  A – O – PB-H2. A – O – P  A – B + H2OPNet Reaction: A – OH + B – H + ATP  A – B + ADP + P + H2O-Coupling reactions to redox of NAD/NADP-Spontaneous Reactions-Glucose + 6O2  6CO2 + 6H2O -Delta G= -686 kcal/mole -This oxidation reaction has a very large, negative DG. Therefore, according to the Second Law, it can proceed “spontaneously.” -A large amount energy is dispersed during this oxidation. If simply burnt, the energy is lost as heat. -Cells carry out this process in many steps to harness some of the energy for chemical work. Oxidation of glucose not very efficient.Enzymes-Activation Energy-Enzyme lowers activation energy for catalyzed reactions-Even energetically favorable reactions need a boost Enzymes supply the boost -Enzymes (usually proteins) increase the rate of reactions by reducing the activation energy-Enzymes are the same before and after the reaction-Enzymes do not change the equilibrium point for a reaction, only the reaction rate-Enzymes lower the activation energy for both the forward and reverse reactions by the same