Different enzymes catalyse specific reactions. Explain why enzymes can only catalyse specific reactions.

A simple way of thinking about why enzymes catalyse only specific reactions is to think of the enzyme and the substrate (the compound the enzyme is acting upon) as a lock and key system. Enzymes have a particular part called the active site, which is where the enzyme acts on the substrate and the reaction takes place. This active site on the enzyme is the lock while the key would be the substrate. Because enzymes are proteins, they have a very specific order of amino acids that make up their structure (including the active site), meaning that only one key can fit in. The active site, or "lock" will recognise the substrate or "key" and will only let that one in and therefore can only catalyse a specific reaction.