Enzymes are substrate specific proteins which act as biological catalysts and as temperature increases, we see an increase in enzyme activity. This occurs because an increase in temperature causes molecules to move faster, increasing the likelihood of successful collisions between the specific substrate and the active site of the enzyme. Enzyme activity will increase with temperature until it reaches its optimum temperature where activity and rate of reaction is at its highest. After this optimum temperature, enzyme activity rapidly decreases due to denaturation. Denaturation is an irreversible change occurring when the bonds holding the enzyme together are broken, causing a change in the shape of the active site. This change means that the specific substrate can no longer fit with the enzyme's active site and enzyme activity decreases.