Study Notes
Enzymes are globular proteins that act as biological catalysts, accelerating chemical reactions without being consumed. They have specific active sites where substrates bind, forming enzyme-substrate complexes. The Lock and Key Hypothesis suggests that enzymes and substrates fit together precisely like a key in a lock. Example: The enzyme sucrase only binds to the substrate sucrose. Induced-fit Hypothesis — proposes that the active site of an enzyme changes shape slightly to fit the substrate better. Example: Hexokinase changes shape when glucose binds to it. Activation Energy — the energy required to start a reaction, which enzymes lower to speed up reactions. Example: Enzymes reduce the activation energy needed for the breakdown of hydrogen peroxide by catalase.
Exam Tips
Key Definitions to Remember
- Enzyme
- Active site
- Enzyme-substrate complex
- Activation energy
- Lock and Key Hypothesis
- Induced-fit Hypothesis
Common Confusions
- Confusing the Lock and Key Hypothesis with the Induced-fit Hypothesis
- Misunderstanding how enzymes lower activation energy
Typical Exam Questions
- What is the Lock and Key Hypothesis? It is the idea that enzymes and substrates fit together precisely like a key in a lock.
- How do enzymes lower activation energy? Enzymes lower activation energy by stabilizing the transition state and reducing the energy needed for the reaction.
- What happens to an enzyme at extreme pH levels? The enzyme may denature, altering the active site and preventing substrate binding.
What Examiners Usually Test
- Understanding of enzyme specificity and active sites
- Differences between Lock and Key and Induced-fit Hypotheses
- How enzymes affect reaction rates and activation energy