a catalyst is a substance which increases the speed of a reaction without being changed or used in the reaction
enzymes are biological catalysts which speed up chemical reactions
every enzyme has an active site with a unique shape that fits onto the substance involved in a reaction
for the enzyme to work the substrate has to fit into its active site. if the substrate doesnt match then the reaction wont be catalysed
changing the temperature changes the rate of an enzyme-catalysed reaction
if it gets too hot some of the bonds break changing the shape of the active site so the substrate no longer fits. the enzyme is denatured
all enzymes have an optimum temperature that they work best at
if the PH is too high or too low it interferes with the bonds holding the enzyme together. this changes the shape of the active site and denatures the enzyme
all enzymes have an optimum PH which is often PH7 but not always
