The enzymes' structure is extremely important to how it functions. The enzyme itself is shaped a specific way so that the substrate (the food) can be broken down. The substrate fits into the active site of the enzyme like a lock and key.An enzyme will not work on a substrate that it does not fit with. When the enzyme is exposed to heat or the wrong pH, it will denature and will not fit with its substrate to break it down. Thus, the enzyme substrate complex will not be formed, breaking down the substrate into the products of chemical digestion.