Enzymes are large globular proteins with specificity. They combine with an complementary substrate to form an enzyme-substrate complex (ESC).
They are biological catalysts – they lower the activation energy needed for a particular biological reaction to occur. The activation energy is the minimum amount of energy needed to start a reaction – this is usually provided by heating.
However, enzymes can lose their ability to function – this is called denaturing. This occurs when the hydrogen bonds are broken, and the tertiary structure changes. Therefore, it can no longer catalyse that specific biological reaction.
What else do you think can cause an enzyme to denature?