in step 1, the substrate fits into the active site in the enzyme, in step 2, only the substrate with the complementary shape can fit into the enzyme and this forms the enzyme-substrate complex , the substrate is the key and the enzyme is the lock, this is the lock and key hypothesis, in step 3, while the substrate is attached to the enzyme, a chemical reaction occurs and the substrate is converted into its products, in step 4, the products then leave the active site, and the enzyme remains unchanged it can now catalyse another reaction
