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Lecture 4 Biochem - Bioenergetics The quantitative study of...

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Bioenergetics The quantitative study of how organisms gain and use energy If you want to understand bioenergetics, you have to understand thermodynamics….so lets review some thermodynamics… System: Could be a bacterial cell, a petri dish of bacteria cells, the earth, or the entire universe…that which is under study System can be isolated (constant V and P) or open Surroundings - that which is in the vicinity of the system, or everything excluding the system under study
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How do organisms obtain energy…. Metabolize food Sunlight - photosynthesis What do organisms use the energy from these types of processes for… Use for heat (to maintain body temperature), walk, breathe, send impulses along nerves, pump ions across membranes… some are obvious uses, some not so obvious…
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Exchange of heat and work in constant-volume and constant-pressure reactions. First Law of Thermodynamics: Internal Energy Change (E = q-w). At constant P, w = PV, q = E + n*RT Statement of the conservation of energy, it’s a bookkeeping rule. When a physical or chemical process occurs, total incomes and expenditures of energy must be equal. Heat = q + = system absorbs heat (endothermic) - = system releases heat (exothermic) - Work = w + = work done by system - = work done on system Energy change = E
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Consider a biochemical example, the oxidation of palmitic acid: CH 3 (CH 2 ) 14 COOH (s) + 23O 2 (g) 16CO 2 (g) + 16 H 2 O (l)
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E = q q = 9941.4 kJ/mol For (b) 23 moles of gas gives 16 moles of gas, so V decreases Surroundings do work on system, at end more heat is given off W = -17.3 kJ/mol, so q = (-9941.4 - 17.3) kj/mol = -9958.7 kJ/mol q = ∆ E + w q = ∆ E + P V q = ∆ E + nRT
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Enthalpy (H) H = E + PV At constant V, H = q At constant P, H = E + PV Heat obtained by oxidizing palmitic acid in an animal is the heat evolved at constant pressure, q = -9958.7 kJ/mol. When heat of reaction is measured at constant P it is H that is obtained. In this example, the difference in heat is 0.2% (the P V term). Most biochemical reactions occur in solution and don’t consume or generate gasses, so P V term is zero and can think of H as E. Do systems always go to the lowest energy state? Not all
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Lecture 4 Biochem - Bioenergetics The quantitative study of...

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