We have seen that enzymes have a definite three-dimensional shape which is complementary shape to the material that the enzyme acts on, the substrate. The first step in any enzyme- catalyzed reaction is the formation of an enzyme-substrate complex. The substrate attaches to the region of the enzyme known as the active site. A chemical reaction then takes place with the formation of the products. The enzyme is then free to react again with any available substrate.

Anything that interferes with the formation of the enzyme-substrate complex can reduce the amount of product from that enzyme. Later in the class we will be discussing drugs. The enzyme/substrate model will be especially useful then. Many drugs function by inhibiting enzyme activity. The drug will fit into the active site much like the substrate and block the reaction normally catalyzed by the enzyme. Suppose a certain Enzyme makes Insulin (a small protein hormone). A drug that inhibits the action of that enzyme would prevent the formation of Insulin. Symptoms after taking that drug would be similar to Diabetes.

Many drugs compete with the substrate for active site binding and prevent the substrate from entering the active site. Unlike the substrates, which exit the active site after the reaction, many enzyme inhibitors remain in the active site indefinitely. This permanently prevents the enzyme from doing its job. A change in the shape of the enzyme can also prevent it from catalyzing reactions.

Enzyme function is dependent on substrate active site interactions. If the substrate doesn't fit..... no reaction. When we discuss Genetics we will examine how the shape of an enzyme gets changed. Here's a hint, Genes, Mutations and Genetic Disorders. Nova Movie (Large File)

Next look at some Protein Hormones.