INTRODUCTION

If we were to extract the chemicals from a living cell and watch them react with one another, we'd probably have to wait a long time—perhaps longer than the normal life of the cell—to see many reactions take place. On their own, many of the chemicals react too slowly to support an organism's metabolism. Living cells circumvent this problem by producing biological catalysts, called enzymes. Enzymes lower the amount of energy required (activation energy) to trigger chemical reactions, making reactions more likely to occur and thereby increasing reaction rates. In the accompanying animation, we look at a reaction in which an enzyme holds a substrate molecule at the enzyme's active site and facilitates the molecule's conversion into a product. We will examine the relative rates of this reaction in the presence or absence of the enzyme, as well as in the presence of enzyme inhibitors.

Video titled: Animation 8.1: Enzyme Catalysis

Transcript Area

CONCLUSION

A variety of molecules can affect the rates of enzyme-catalyzed reactions. This animation focuses on chemical inhibitors that cause reversible inhibition. That is, they can bind and thereby inhibit the action of the enzyme, and then they can become unbound, allowing the enzyme to function again.

Competitive inhibitors bind to the active site of the enzyme, preventing substrate binding. This type of inhibition can be overcome by increasing the concentration of substrate molecules, because the inhibitor and substrate compete for the same binding site.

Uncompetitive inhibitors bind to the enzyme after the substrate has already bound. Uncompetitive inhibitors prevent the release of products. This type of inhibition is not overcome by an increase in substrate concentration.

Noncompetitive inhibitors bind at a site other than the active site, changing enzyme structure so that normal substrate binding cannot occur. This type of inhibition is not overcome by an increase in substrate concentration.

Textbook Reference: Key Concept 8.5 Enzyme Activities Can Be Regulated

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