Bioenergetic1 - Bioenergetics Bryant Miles Basis of...

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Bioenergetics Bryant Miles Basis of Thermodynamics Every living cell and organism must perform work to stay alive, to grow and to reproduce. The ability to harvest energy from nutrients or photons of light and to channel it into biological work is the miracle of life. Living organisms carry out a remarkable variety of energy transductions. The biological energy transductions obey the physical laws that govern all natural processes, including the laws of thermodynamics. 1 st Law of Thermodynamics The energy of the universe remains constant. 2 nd Law of Thermodynamics All spontaneous processes increase the entropy of the universe. State functions depend only on the initial and final conditions not on path taken between the initial and final conditions. They are independent of path . The important state functions for the study of biological systems are: G, the Gibbs free energy which is equal to the total amount of energy capable of doing work during a process at constant temperature and pressure. If Δ G is negative, then the process is spontaneous and termed exergonic. If Δ G is positive, then the process is nonspontaneous and termed endergonic. If Δ G is equal to zero, then the process has reached equibrium. H , the Enthalpy which is the heat content of the system. When Δ H is negative the process produces heat and is termed exothermic. When Δ H is positive the process absorbs heat and is termed endothermic. S , the Entropy is a quantitative expression of the degree of randomness or disorder of the system. When Δ S is positive then the disorder of the system has increased. When Δ S is negative then the disorder of the system has decreased. The conditions of biological systems are constant temperature and pressure. Under such conditions the relationships between the change in free energy, enthalpy and entropy can be described by the expression where T is the temperature of the system in Kelvin. Δ G = Δ H T Δ S Equilibrium Constants All spontaneous processes proceed until equilibrium is reached. Consider the following chemical reaction. A + B C + D k 1 k 2 The forward rate of product formation is = k 1 [A][B] The reverse rate of reactant formation is = k 2 [C][D] At equilibrium the concentrations of products and reactants are such that forward and reverse rates are equal k 1 [A eq ][B eq ] = k 2 [C eq ][D eq ]. A little algebra and presto
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] ][ [ ] ][ [ 2 1 eq eq eq eq eq B A D C k k K = = At equilibrium Δ G = 0. The biochemist standard state the concentration of reactants and products are initially set at 1 M, the temperature is 298 o K, the pressure is 1 atm, the pH is 7.0 and the concentration of water is 55 M. The biochemists constants are written as Δ G o ’ and K’ eq . This is the only standard state we will work with in this class so forgive if I occasionally drop the prime. Δ G o ’ is a constant characteristic for each reaction just as K’ eq is a constant characteristic for each reaction. These two constants have a simple relationship.
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This note was uploaded on 04/11/2010 for the course BICH bich 411 taught by Professor Bryantmiles during the Spring '10 term at Texas A&M.

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Bioenergetic1 - Bioenergetics Bryant Miles Basis of...

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