1. Enzymes are proteins that accelerate biochemical reactions without being altered. They have high substrate specificity and increase reaction rates by lowering activation energy. 2. The active site of an enzyme is complementary to its substrate. Substrate binding occurs through lock-and-key or induced-fit models. 3. The rate of enzyme reactions is affected by substrate and enzyme concentration, temperature, and pH. Higher concentrations and temperatures increase rates while deviating from optimal pH decreases rates.