Effect of Temperature

Temperature affects enzyme activity in two opposing ways.Up to the optimum: raising the temperature gives the enzyme and substrate molecules more kinetic energy. They move faster and collide more often, so more enzyme-substrate complexes form per second and the rate increases. For many reactions the rate roughly doubles for every 10 °C rise.The optimum temperature is the temperature at which the rate is fastest. For many human enzymes it is close to 37 °C.Above the optimum: the atoms in the enzyme vibrate more strongly. This breaks the hydrogen and ionic bonds that hold the tertiary structure. The shape of the active site changes, so the substrate no longer fits and fewer enzyme-substrate complexes form. The enzyme is denatured. Denaturation is permanent, so the rate falls steeply.At low temperatures enzymes are inactive, not denatured. They work again when warmed.The temperature coefficient, Q₁₀, compares rates 10 °C apart:Q₁₀ = rate at (T + 10 °C) ÷ rate at TWorked example: the rate is 4 units at 20 °C and 8 units at 30 °C, so Q₁₀ = 8 ÷ 4 = 2. If Q₁₀ = 2 and the rate at 25 °C is 3.0 units, the rate at 35 °C is 3.0 × 2 = 6.0 units.