Overview Kinetic theory for two molecules to react they must be within bond-forming distance possess enough kinetic energy to overcome the activation energy (Ea) factors that affect these two conditions will either decrease or increase the reaction rate temperature: causes an increase in kinetic energy concentration of reactants: increases probability of collisions Gibbs free energy change (ΔG) is the free energy change between the products and the reactants reflects the direction of a reaction and amount of reactants and products at equilibrium, but does NOT determine the rates of reaction ΔG < 0: reaction is spontaneous and favors product formation ΔG = 0: reaction is at equilibrium and proceeds in both direction at equal rates ΔG > 0: reaction is nonspontaneous and favors reactant formation Ea determines the rate of the reaction a large Ea will have a slower rate a small Ea will have a faster rate enzymes lower the Ea allowing the reaction to proceed at a faster rate enzymes do NOT change the ΔG of the reaction just the Ea enzymes are sensitive to temperature and pH Enzymes Kinetics Michaelis-Menten Equation an equation that relates the initial reaction velocity (Vi) to the substrate concentration Vmax is directly proportional to the [E] Km is the Michaelis-Menten constant which represents the substrate concentration at which Vi is half the maximum velocity (Vmax) Km = [S] at 1/2 Vmax Km is related to the enzyme's affinity for the substrate [S] ↑ Km = ↓ affinity ↓ Km = ↑ affinity inhibitors affect these enzyme parameters competitive increases Km noncompetitive decreases Vmax Lineweaver-Burk Equation an inverted form of the Michaelis-Menten equation used to calculate Vmax and Km from experimental data at below enzyme saturation levels the equation is in the format y = ax + b (a is the slope and b is the y intercept) y = 1/Vi x = 1/[S] a = Km/Vmax b = 1/Vmax helpful hints the smaller value of -1/Km, the greater the Km ↑ y-intercept = ↓ Vmax