Reactants of a chemical reaction need to gain energy before they can undergo the reaction. This required energy is called the activation energy of the reaction and it is needed to break bonds within the reactants. At a later stage in the reaction energy will be released as new bonds form. The majority of biological reactions are exothermic. In exothermic reactions the energy released by the new bonds formed is greater than the activation energy. In other words, the reaction releases energy. Enzymes make it easier for reactions to occur by decreasing the activation energy required in the reactions that they catalyse.

Competitive Inhibitors
These are structurally similar to the substrate of the enzyme and bind to the active site. This means that when a competitive inhibitor binds to the active site of an enzyme, it prevents the substrate from binding to the active site. Only once the inhibitor has been released from the active site can the substrate bind. The inhibitor is called a competitive inhibitor as it competes with the substrate for the active site.

The effects of a competitive inhibitor can be reduced by increasing the substrate concentration. More substrate would successfully bind to the active site than inhibitor and therefore reducing the effect of the inhibition. The maximum rate of reaction or a level very close to the maximum rate of reaction can be reached.
Non-Competitive Inhibition
These are not similar to the substrate and they do not bind to the