1. Enzyme Action
Objective: To understand the role of enzymes in
the body and how they function.
Outcomes:
Recall the function of enzymes.
Describe the structure of enzymes.
Compare the two different models that
explain how enzymes work.
Sunday, 28 September 2014
Keywords
Active site
Substrate
Enzyme-substrate
complex
Lock and key model
Induced fit model

2. Enzymes
Globular proteins that catalyse chemical reactions in living
organisms (biological catalysts):
Properties
Specific (tertiary protein structure)
Increase rate of the reaction
Unchanged at the end of the reaction
Need them Reactions too slow to maintain life

3. Enzymes are specific
A substrate is a reactant which binds to an enzyme.
When a substrate or substrates binds to an enzyme, the enzyme
catalyzes the conversion of the substrate to the product.
e.g. Sucrase is an enzyme that binds to sucrose and
breaks the disaccharide into fructose and glucose.

4. The active site of an enzymes is typically a pocket or groove on
the surface of the protein into which the substrate fits.
The specificity of an enzyme is due to the fit between the active
site and that of the substrate.

5. Models of enzyme action
The lock and key model The induced fit model
Use page 31 and 32 to create a
table/diagram/notes
summarising the differences
between these two models of
enzyme action.

6. The lock and key model
Substrate
molecules
Enzyme is rigid.
Active site Enzyme
Reaction happens (bonds
either made or broken)
Product
Enzymes have a specific 3D
structure
Enzyme-substrate
complex

7. But…
Other molecules could bind to enzymes at different sites.
This altered the activity of the enzyme.
The enzyme was flexible.

8. Models of enzyme action
The induced fit model
• The active site fits to the substrate,
and the enzyme changes shape
slightly.
• This interaction is called induced fit.

9. Enzyme Action
Scientists often try to explain their observations by producing a representation of how something works. This is known as a scientific model.
The lock and key model The induced fit model