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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. 485 – 509, 512 - 521. 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. 487) to distinguish between catabolic and anabolic pathways. 2. Δ G = Δ H - T Δ S a. Name and define each of the terms in the above equation (pp. 490 - 491). What units are used for each of these terms? (Note this equation is almost never used by biochemists because we work at one temperature and don't measure heat formation.) b. Distinguish between Δ G, Δ G°, and Δ G'° (p. 491).
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2 3. Δ G'° = -RT ln K'eq a. What is the sign of Δ G'° when the reaction proceeds in the written direction (p. 492)? b. Δ G is determined by measuring the equilibrium constant. Using the sample calculations on pp. 492 and 494 - 495 as a guide, do problems 2, 3, and 6 (pp. 522 - 524). c. Using Table 13-4 (p. 493), compare the free energy content of acid anhydride and ester bonds. 4. Of the equations shown in the textbook, the Gibbs equation is the most useful for biochemists because it involves concentrations which can be measured (equation 13-4; p. 493). To analyze the energetics of a pathway in vivo we first measure Keq in vitro , calculate Δ G'° and then measure Δ G in vivo by measuring the concentrations of products and reactants and applying equation 13-4. G = G’° + RT ln ([C][D] / [A][B]) 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 (p. 494)? c.
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