Enzymes and substrates share specificity in that an enzyme will only react with a specific substrate • This is because the active site is complementary in both shape and charge to a given substrate • The model by which this is known is ‘lock and key’ as the substrate is a precise structural fit for the enzyme, much like a lock and key • When the enzyme and substrate bind, they form an enzyme-substrate complex, before the substrate is catalytically converted into a product