Products + 1. 2. The place on the enzyme where the substrate fits is called the active site. 3. The lock and key model states that, in the same way a key fits into a specific lock, the substrate fits into the active site of a specific enzyme. 4. 5. 6. As temperature increases the substrate and enzyme molecules have more kinetic energy therefore more chance of successful collisions. 7. 8. Every enzyme also works best at a specific pH – the optimum pH.