Enzymes and Their Functionality

Challenges in Observing Enzymes

• Enzymes are extremely small and cannot be observed directly, even with electron microscopes.
• Microscopes provide still images, not real-time movement.

Modeling Enzyme Function

• Models are used to describe and understand enzyme functionality.
• Two main models: Lock and Key Model and Induced Fit Model.

Lock and Key Model

• Compares enzyme and substrate to a lock and key mechanism.
  • Enzyme active sites are specific and complementary to substrates.
  • Important to note: shapes are complementary, not identical.
• Enzyme-Substrate Complex: Forms when enzyme and substrate bind.
  • Temporary linkage; reduces activation energy for reactions.
  • Enzyme remains unaffected and reusable after the reaction.
• Limitations:
  • Only substrates with complementary shapes can bind.

Induced Fit Model

• Suggests that enzyme active sites are flexible, not rigid.
• Active site can change shape to fit various substrates.
• Allows formation of enzyme-substrate complex even if initial shapes are not complementary.
• Active site returns to original shape after reaction.
• Advantage: Can react with multiple substrates due to flexibility.

Comparison of Models

• Lock and Key Model: Fixed active site, specific to one substrate.
• Induced Fit Model: Flexible active site, can accommodate various substrates.
• Enzymes can follow either model depending on the situation.
  • No need to know which enzymes follow which model; understand the concepts and differences.

Similarities Between Models

• Both models allow formation of enzyme-substrate complex.
• Both models lower the activation energy for reactions.
• Enzymes are reusable after converting substrates to products.