1. Lock and Key Model Enzymes are specific to their substrates Substrate and active site match each other in two ways: Structurally  substrates that don’t fit in the active site won’t react Chemically  substrates that are not chemically attracted to the active site won’t react

2. A different model: Induced Fit Allows for some enzymes being able to catalyze multiple reactions As the substrate approaches the enzyme, it changes shape to fit the substrate This stresses the substrate, reducing the activation energy of the reaction

3. Enzyme Inhibition - Competitive Inhibitor molecules have shapes very similar to substrate molecules These molecules compete for the active site on the enzyme If the active site is filled with a competitive inhibitor, the reaction is slowed down or stopped completely Ex…antibiotics (penicillin)

4. Effect on Reaction Rate The higher the concentration of inhibitor, the slower the rate of reaction

5. Enzyme Inhibition – Non-competitive Inhibitor molecules bind to a site other than the active site  the regulatory site The shape of the active site is changed as a result The substrate can no longer fit into the active site Ex…Heavy metals (Pb, Hg)

6. Effect on Reaction Rate As concentration of inhibitor increase, the rate of reaction decreases because there are fewer functional active sites available for reaction