Lowering of Activation Energy (College Board AP® Biology)

Enzymes as Biological Catalysts

• Enzymes are biological catalysts

  • ‘Biological’ because they function in living systems

  • ‘Catalysts’ because they speed up the rate of chemical reactions without being used up or changed

Graph to Show How Enzymes Lower Activation Energy

The activation energy of a chemical reaction is lowered by the presence of a catalyst (ie. an enzyme)

Enzymes work by lowering the activation energy of a reaction

• All chemical reactions are associated with energy changes

• For a reaction to proceed there must be enough activation energy

• Activation energy is the amount of energy needed by the substrate to become just unstable enough for a reaction to occur and for products to be formed

  • Enzymes speed up chemical reactions because they influence the stability of bonds in the reactants

  • The destabilization of bonds in the substrate makes it more reactive

• Enzymes work by lowering the activation energy of a reaction and in doing so they provide an alternative energy pathway