1. ENZYMES Each enzyme lowers the activation energy of the reaction it catalyses. The induced-fit model of enzyme action. The properties of an enzyme relate to the tertiary structure of its active site and its ability to combine with complementary substrate(s) to form an enzyme-substrate complex. The specificity of enzymes Students should be able to: appreciate how models of enzyme action have changed over time appreciate that enzymes catalyse a wide range of intracellular and extracellular reactions that determine structures and functions from cellular to whole-organism level.

2. Enzymes  Exam Question: Explain how protein structure is determined and its importance. (10+ marks) Outcomes: -Define the term enzyme and its function. -Use diagrams to explain the structure of an enzyme and describe how it works -Use stages to explain the mechanism of enzyme action. -Explain how models of enzyme action developed and change over time.

3. Structure of an enzyme  Enzymes are catalysts:  They help break down or build up molecules in reactions  they allow reactions to happen more easily at lower activation energy.  Enzymes are globular proteins. They have quaternary structures.  Active site – made up mostly of the R groups of some of the amino acids  Allosteric site Outcomes: -Define the term enzyme and its function. -Use diagrams to explain the structure of an enzyme and describe how it works -Use stages to explain the mechanism of enzyme action. -Explain how models of enzyme action developed and change over time.

4. Lock and Key model 1. Substrate joins at the active site by hydrogen bonding 2. Forms an enzyme-substrate complex 3. Bonds broken in the substrate to break it down. Substrate is turned into products 4. Products bonded to enzyme are released from enzyme 5. Enzyme ready to break down next substrate. Q: Why is shape important here? Q: Why are enzymes specific to their substrate? COMPLIMENTARY SHAPE Outcomes: -Define the term enzyme and its function. -Use diagrams to explain the structure of an enzyme and describe how it works -Use stages to explain the mechanism of enzyme action. -Explain how models of enzyme action developed and change over time.

5. Induced fit model Outcomes: -Define the term enzyme and its function. -Use diagrams to explain the structure of an enzyme and describe how it works -Use stages to explain the mechanism of enzyme action. -Explain how models of enzyme action developed and change over time.

6. Task:  In a table identify the differences between the lock and key model and induced fit model of enzyme action: Outcomes: -Define the term enzyme and its function. -Use diagrams to explain the structure of an enzyme and describe how it works -Use stages to explain the mechanism of enzyme action. -Explain how models of enzyme action developed and change over time. Lock and KeyInduced fit Active site is rigidActive site is flexible Active sites fit is exact with substrate Active site molds around substrate Substrate binds to enzyme and enzyme breaks substrate bonds Binding of substrate causes change in shape of enzyme which starts the bond breaking process.

7. Why is the induced fit model a better model?  The induced fit model is more accepted because:  It is known protein shapes are changeable due to hydrogen bonds and van-der waals forces.  It explains why products are released easily as their shape has been changed in a way that the active site can no longer mold/accommodate them. Outcomes: -Define the term enzyme and its function. -Use diagrams to explain the structure of an enzyme and describe how it works -Use stages to explain the mechanism of enzyme action. -Explain how models of enzyme action developed and change over time.

8. HW:  Make a model of an enzyme.  Include in your model, the ideas of:  The active site  Enzyme specificity and complimentary shapes for the active site.  Enzyme substrate complex  The allosteric site CAKE IS A GOOD IDEA!