Key_Unit2_chapterproblems - Gerhart Key for Unit 2 review...

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Gerhart 11/5/2010 Key for Unit 2 review questions found at the end of the chapters The answers to a selection of the review questions are given below. Catalysts 1a. This value, together with the concentrations of the A and B dictate the rate of the forward reaction (choose one from a, b, c, d, or e above). What is the name for this value? B or C (energy of activation of the forward reaction, either with or without the enzyme). 1b. This value is unaffected by heat or the presence of a catalyst (choose one from a, b, c, d, or e above). What is its name? D (change in free energy, or Δ G) 1c. At equilibrium this value dictates the value of the ratio ([A] x [B]) / ([C] x [D]) (choose one from a, b, c, d, or e above) D (change in free energy determines whether reactants or products are energetically favored) 2. Explain the lock and key model of enzyme function, including the role played by the active site of the enzyme. The active site of an enzyme provides a 2- or 3-dimensional surface, or pocket, that fits the shape of the substrate rather like a key fits into a lock. The active site positions the substrate so that it is more likely to react, and may interact with the substrate to tweak its bonds, add or subtract electrons from the substrate, and otherwise lower the energy required for the substrate to reach the transition state energy level. 3. Draw an energy profile (like that shown in the figure for question 1) for an endergonic reaction. Alter the profile to show the affect of an enzyme. Label energy of activation, transition state, products, reactants, and Δ G. It’s essentially the diagram above, but flipped horizontally so that reactants have less energy and products more. In other words, run the reaction above in reverse to get the answer to this question. Metabolism / Chemistry basics 1. When a chemistry book presents electron shells, it generally emphasizes that shells represent distinct energy levels. Electron shells are also said to represent distance from the positive charges in the nucleus. Are these two viewpoints contradictory? Why or why not? The two viewpoints are not contradictory. Electrons that are further from the nucleus have more energy. This is because electrons are attracted to protons, and forcing electrons further from the protons thus requires an input of energy (or an opposing force, such as negatively charged electrons that have all ready occupied the shells closer to the nucleus). 2. Refer to the figure to answer the following questions. a. Is the forward reaction exergonic (releasing energy overall) or endergonic (requiring net energy input)?
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Gerhart 11/5/2010 b. Is the forward reaction spontaneous? Yes c. Which arrow represents the activation energy for the forward reaction? a d. Which arrow represents the activation energy for the reverse reaction? c e. Which arrow represents the overall free energy change ( Δ G) for the reaction? b f. Are the products of this reaction “stable”? How can you tell? Yes, in that there is a
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This note was uploaded on 03/08/2011 for the course BIS 2A taught by Professor Grossberg during the Fall '08 term at UC Davis.

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Key_Unit2_chapterproblems - Gerhart Key for Unit 2 review...

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