03 - Chapter 3 Thermodynamics of Biological Systems ....

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Chapter 3 Thermodynamics of Biological Systems . . . . . . . . . . . . . . . . . . . . . . . . Chapter Outline v Thermodynamic concepts Systems Isolated systems cannot exchange matter or energy with surroundings Closed systems exchange energy but not matter Open systems exchange both energy and matter First Law: •E = q + w •E = change in internal energy (state function), q = heat absorbed, and w = work done on the system H = E + PV: H = enthalpy (energy transferred at P=constant): •H = q when work limited to P•V •Hº = -Rd(lnK eq )/d(1/T): van’t Hoff plot RlnK eq vs 1/T (R = gas constant = 8.314J/mol K Second Law: Disorder or randomness S=klnW where k = Boltzmann’s constant = 1.38x10 -23 J/K, W = number of ways of arranging the components of a system at •E = 0. dS = dq/T for reversible process Third law: Entropy of a perfectly ordered, crystalline array at 0 K is exactly zero S = C p dlnT 0 T , C p = heat capacity = dH/dT for constant P process Gibbs free energy: •G = •H + T•S •G = •G° + RTln([P]/[R]) and •G° = -RTln([P] eq /[R] eq ) When protons involved in process: •G°’=•G° ± RTln[H + ] (“+” if reaction produces protons; “-” if protons consumed) v Coupled processes: Enzymatic coupling of a thermodynamically unfavorable reaction with a thermodynamically favorable reaction to drive the unfavorable reaction. Thermodynamically favorable reaction is often hydrolysis of high-energy molecule v Energy transduction: high-energy phosphate ATP and reduced cofactor NADPH Phototrophs use light energy to produce ATP and NADPH Chemotrophs use chemical energy to produce ATP and NADPH v High-energy molecules Phosphoric anhydrides (ATP, ADP, GTP, UTP, etc.) Enol phosphates (phosphoenolpyruvate a.k.a. PEP) Phosphoric-carboxylic anhydrides (1,3-bisphosphoglycerate) Guanidino phosphates (creatine phosphate) v Why is hydrolysis of high-energy bonds favorable Destabilization of reactant due to electrostatic repulsion Product isomerization and resonance stabilization Entropy factors v Thermodynamics of ATP hydrolysis influenced by: pH, cation concentration, reactant and product concentrations
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Chapter 3 . Thermodynamics of Biological Systems 30 Chapter Objectives Laws of Thermodynamics The first law of thermodynamics is simply a conservation of energy statement. The internal energy changes if work and/or heat are exchanged. In biological systems, we are usually dealing with constant-pressure processes and in this case the term enthalpy, H , is used. Enthalpy is the heat exchanged at constant pressure. Since enthalpy is heat, it is readily measured using a calorimeter or from a plot of R(lnK eq ) versus 1/T, a van't Hoff plot. (To get ahead of the story, the point is that if •G and •H are known, •S can be calculated.) The second law of thermodynamics introduces the term entropy, S , which is a measure of disorder or randomness in a system. A spontaneous reaction is accompanied by an increase in
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03 - Chapter 3 Thermodynamics of Biological Systems ....

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