3.2: Enzyme Catalysis

Topic 3.1 introduced enzymes and their reactions. You learned that enzymes catalyze reactions by reducing the activation energy of the processes. Topic 3.2 explains how enzymes do that, as well as the different classifications of reactions.

Vocab List

• Lock and Key Model (outdated)
• Induced Fit Model
  • Conformational change
• Exergonic reaction
  • Catabolic
  • Exothermic
• Endergonic reaction
  • Anabolic
  • Endothermic

Written Explanation

Catalysis models:

When scientists were first learning about enzymes, they believed that the substrate perfectly fit inside an enzyme's active site. This was the lock and key model. However, this model is slightly inaccurate. Besides it being observationally incorrect (the substrate never actually perfectly fits to an active site), the lock and key model fails to explain how an enzyme actually acts as a catalyst and reduces activation energy.

More recently, scientists have turned to the induced fit model. This model states that when a substrate binds to an enzyme's active site, both it and the enzyme slightly change shape to create a more ideal fit. It's this change in shape that serves to reduce the activation energy by placing stress on the bonds of the substrate or pushing substrates together. The change in shape of this type of reaction is called a conformational change (the enzyme and substrate "conform" to each other).

It is important to remember that although enzymes lower the activation energy of a reaction, they do not change the overall release or storing of energy which takes place through the reaction.

Types of reactions: