Unit10 - Unit 10 1 UNIT 10 PART A: BIOENERGETICS PART B:...

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Unit 10 1 U NIT 10 P ART A: B IOENERGETICS P ART B: C HEMISTRY OF C ARBOHYDRATES P ART C: G LYCOLYSIS P ART A: B IOENERGETICS Assignment: Nelson & Cox, pp. 481 – 503, 507 - 517. All living cells must obtain energy from their surroundings and expend it as efficiently as possible. Plants gather most of their energy from sunlight; animals use the energy stored in plants or other foods that they consume. The processing of this energy is central to the understanding of biochemistry. Bioenergetics, the quantitative analysis of how organisms gain and utilize energy, is a special part of the general science of energy transformation which is called thermodynamics. 1. Use Fig. 3 (p. 483) to distinguish between catabolic and anabolic pathways. 2. Of the equations shown in the textbook, the Gibbs equation is the most useful for biochemists (equation 13-3; p. 494). G = G’° + RT ln ([C][D] / [A][B]) (Note that the terms G’° and G°’ used elsewhere are the same.)
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2 The term, Δ G'° is different from the chemist's Δ G° in that the standard state is at a pH of 7.0 (or other specified value) instead of a pH of zero. The equation, a quantitative version of Le Châtelier's principle, shows the relationship of the free energy of a reaction to the concentration of reactants and products. The logarithmic term in the equation comes from an integration of the ideal gas law used in calculating the free energy necessary to compress a gas. The units of Δ G are Kcal/mol (or KJoules/mol). Both units are commonly used but the use of Joules is increasing. 1 cal.= 4.184 J. (Note that the Calorie used for food is one Kcal!) a. Which term in the Gibbs equation can be used to predict whether a reaction will proceed? Note : It is Δ G, not Δ G , which determines whether a reaction will go spontaneously or not. Thus, why do the authors of most texts talk about coupled reactions, thermodynamic feasibility, etc . in terms of Δ G ? The reason is mostly a matter of convenience because these values can easily be looked up in tables. Sometimes Δ G and Δ G'° can, however, be very different! For example, one reaction in the citric acid cycle has a Δ G'° of +7.1 Kcal/mol and a negative Δ G. Although the Δ G'° would not suggest it, the reaction occurs spontaneously in the citric acid cycle due to the concentration term in the Gibbs equation. b. What does Δ G tell you about the rate of the reaction? 3. Δ G is determined by measuring the equilibrium constant. G’° = - RT ln Keq Using the sample calculations on pp. 492 and 494 - 495 as a guide, do problems 2 and 11 (pp. 518 - 519). 4. It is possible for a reaction with a positive Δ G'° to be driven by a coupled reaction which has a negative Δ G'°. Explain why this can occur. Using the example on page 501 as a guide, do problem 10 (p. 519). 5.
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This note was uploaded on 04/06/2008 for the course BIOBM 3300 taught by Professor Blankenshi during the Fall '08 term at Cornell University (Engineering School).

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Unit10 - Unit 10 1 UNIT 10 PART A: BIOENERGETICS PART B:...

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