1Problem Set 2-Answer Key BILD1 FA 2008 1)How does an enzyme catalyze a chemical reaction? Define the terms and substrate and active site. An enzyme lowers the energy of activation so the reaction proceeds at a faster rate than if it were uncatalyzed. The enzyme accomplishes this by bringing reactants into closer contact within the active site and facilitating bond breakage or union. The substrate is the molecule bound by the active site of the enzyme and converted into product. The active site is that portion of the enzyme that binds with the substrate molecule to initiate the formation of product. 2) Label the terms A thru E on the energy diagram curve at the right. A = products; B = ΔG; C = transition state or unstable intermediate; D = energy of activation (EA); E = substrates or reactants a)Endergonic b)No, the reaction requires an infusion of energy. c)ΔG > 0 as ΔG = GProducts−GReactants. d)Yes, this reaction is reversible. The reaction can go in the forward manner where the reactant goes to form the product and it can also proceed in the reversed manner where the product is used to form the reactant. The energy diagram suggests that the reverse reaction may be more favorable than the forward. e)Adding an enzyme will lower the activation energy, the amount of energy needed to overcome the energy barrier, and therefore decrease D. An enzyme, by definition, will speed up the rate of the reaction in both the forward and the reverse reactions, as a result does not change the Gibbs free energy of the reactants (E) and the products (A). f)Adding an enzyme does not change the Gibbs free energy. It only increases the rate of the reaction by lowering the activation energy. AC BD E
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