ENZYMES. Enzymes An enzyme is a protein catalyst. Enzymes facilitate reactions without being used up. Lower the activation energy of a reaction. Generally, energy added to a reaction to speed it up is in the form of heat. This is not good for cells – Why?
Enzymes simply decrease the activation energy of a reaction therefore, they will not affect equilibrium nor will they cause a reaction that would not normally occur spontaneously to do so.
As the substrate nears the functional groups of the amino acids in the enzyme protein, the enzyme changes it shape to better accommodate the substrate.