Enzymes are amazing molecules. They are produced by living cells, with each cell containing several hundred enzymes. They are extremely specific, generally reacting with only one substrate. They can speed up the rate of chemical reactions by as much as a million times, by lowering the activation energy without being used up or being unchanged. Within a cell, in the absence of enzymes, reactions would take place at too slow a rate to sustain life. To increase the rate of reactions, high temperatures would be necessary and this would be lethal to the cell.
Activation energy without an enzyme, molecules react by randomly colliding, but energy has to be applied. For a reaction to take place molecules, known as substrates, have to collide with enough energy to break or form bonds, reacting products. The energy required to make substrates react is collide the activation energy. Binding for activity: Substrate molecules bind to the active site of an enzyme. The substrate molecules are usually much smaller than the enzymes. When the substrate binds to the enzyme, they slot neatly into the active site.
This idea is called the lock and key model because the substrates seem to fit into the active site as a key fits into a lock. Temperature: at lower temperatures, 5-30 degrees, increasing the temperature provides more heat energy. This increases the kinetic energy which makes both the substrate molecules and the enzyme molecules move faster. There will be an increase in the number of collisions between the substrate and the active site of the enzyme, resulting in more enzyme-substrate complexes and in turn the formation of more products.
As the temperature continues to increase, to above 40, the enzyme and the substrate molecules move even faster. However, the structure of the enzyme molecule vibrates so energetically that some of the bonds holding the structure together begin to break. The enzymes begin to lose its globular shape, which affects the active site so much so that the substrate will no longer fit in it. The enzyme is said to become denatured and will not regain its correct shape even if the temperature is lowered.