369Lecture13_F11(1)

369Lecture13_F11(1) - Lecture 13 Ch 12 Overview of...

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Unformatted text preview: + Lecture 13: Ch 12 Overview of Metabolism and Free Energy CH369 Fall 2011 1 + Free Energy & Metabolic Reactions n Energy is the capacity to do work n Capacity to produce or undergo change n In biological systems, capacity for chemical change n Free energy is a property of a system n Bonds don’t actually have a certain amount of energy “stored” in them n Look at energy changes associated with a chemical reaction n For reaction: A + B ßà C + D n At equilibrium, no net change in concentration 2 K eq = C [ ] eq D [ ] eq A [ ] eq B [ ] eq + Free Energy & Metabolic Reactions n When not at equilibrium, reactants move to reach equilibrium values n Standard free energy change for reaction, ϶ G°’ n R = gas constant (8.3145 J/K/mol); T = temp (Kelvin) n What is “standard” (°) according to chemistry? n 25°C (298 K) n 1 atm pressure n 1 M n Not relevant for biological systems n Prime (‘) specifies reaction under standard biochemical conditions 3 " G # ° = $ RT ln K eq + Free Energy & Metabolic Reactions n In living cells, conditions seldom “standard” n Define actual change in free energy, ϶ G n At equilibrium, ϶ G = 0 n Spontaneity of reaction related to actual concentrations, not ϶ G°’ n Reaction with ϶ G = + can still occur, depending on reactant concentration 4 " G = " G # ° + RT ln C [ ] D [ ] A [ ] B [ ] " G # ° = $ RT ln K eq + Coupling of Reactions n Thermodynamically unfavorable reactions can proceed in vivo if coupled to favorable reaction n Costs energy to produce Glc-6-P n Couple with ATP hydrolysis n Net effect is thermodynamically favorable ( ϶ G = negative) n VERY common theme in biochemical systems 5 + Importance of ATP n Average human turns over his/her body weight in ATP per day n ATP is involved, directly or indirectly in virtually every area of biosynthesis in cells* n ATP appears to transfer energy from one thing to another n Not really “energy currency” though n Remember – energy is a capacity, not a tangible item 6 *http://onlinelibrary.wiley.com/doi/10.1016/0307-4412%2889%2990012-5/abstract + ATP Hydrolysis n Phosphoanhydride bonds of ATP are just regular covalent bonds n Why are they called “high energy” bonds? n Breaking of bonds produces large negative change in free energy n Why? n Products of hydrolysis more stable than reactants n Negative charges separated n Products have higher resonance stabilization n Greater delocalization of electrons n True of other phosphate derivatives also 7 + Pathway Regulation n Small ϶ G means small fluctuations in reactant and product concentrations n Not a strong drive to proceed in one direction n Large ϶ G have longer way to reach equilibrium n Stronger drive to proceed forward n Enzymes for these reactions work too slowly n Regulate pathway flux by adjusting the reaction rate n é [enzyme] n é activity of enzyme n Allosteric activators 8 + Lecture 13: Ch 13 Glucose Metabolism CH369 Fall 2011 9 + Pathways of Glucose Metabolism n Glycolysis n “Glyco” – “lysis”: breakdown of glucose monomer...
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This note was uploaded on 11/12/2011 for the course CH 369 taught by Professor Kbrowning during the Fall '07 term at University of Texas.

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369Lecture13_F11(1) - Lecture 13 Ch 12 Overview of...

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