How do enzymes affect the rate of reaction?

Enzymes are known as biological catalyst and work by lowering the activation energy of a reaction. They do this by providing an alternative pathway which speeds up the reaction without the catalyst undergoing a permanent change. The substrate binds to the active site of the enzyme allowing an intermediate to be formed which has a lower activation energy than if there was no catalyst. As a globular protein, pH and temperature affect the bonds that hold the enzymes structure making enzymes sensitive to these factors.  An important thing to remember is that enzymes do not affect the equilibrium of a reaction.