1. SBI 4U: Metablic Processes
ENZYMES
Section 1.3

2. SBI 4U: Metablic Processes
Enzyme Introduction
Enzymes are biological catalysts that lower the activation energy of a reaction and in doing so, increase the rate of the reaction.
Most enzymes are proteins.
The name of an enzyme often ends in –ase.
Ex. Amylase (breaks down starch)
Ex. Maltase (breaks down maltose)
Section 1.3

3. SBI 4U: Metablic Processes
Enzyme Introduction
Enzymes catalyze over 4,000 reactions
Each enzyme works only with a specific reactant called the substrate.
Enzymes work best under an optimal range of pH and temperature. Outside of this range they will denature.
Section 1.3

4. Enzyme-Substrate Interaction
SBI 4U: Metablic Processes
Enzyme-Substrate Interaction
The substrate will bind to the active site of the enzyme (a pocket or groove in 3D structure).
There is only one active site on an enzyme.
Enzyme-substrate complex: an enzyme with its substrate attached to the active site.
The enzyme may have an allosteric site as well where inhibitors or activators will bind.
Section 1.3

5. Enzyme-Substrate Interaction
SBI 4U: Metablic Processes
Enzyme-Substrate Interaction
Section 1.3

6. SBI 4U: Metablic Processes
Lock and Key Model
In 1894, Emil Fischer suggested that the enzyme and substrate have complimentary geometric shapes and fit into each other like a key into a lock.
The model explained enzyme specificity but not the stabilization of the transition state, the state between the substrate and the products.
Section 1.3

7. SBI 4U: Metablic Processes
Induced-Fit Model
In 1958, Daniel Koshland modified the lock and key model.
His Induced-fit model states that the substrate causes the enzyme to change its shape to better hold the substrate.
Active sites were seen as ‘flexible’ and not rigid structures like before.
Section 1.3

8. SBI 4U: Metablic Processes
Activation
Some enzymes require a molecule known as an activator to attach to their allosteric site in order for their active site to be receptive to substrate.
Section 1.3

9. SBI 4U: Metablic Processes
Inhibition
Inhibition is when the enzyme’s active site is prevented from binding to a substrate.
There are many different types of inhibition.
Section 1.3

10. Competitive Inhibition
SBI 4U: Metablic Processes
Competitive Inhibition
Competitive Inhibitors: an inhibitor competes with the substrate for access to the active site of the enzyme.
animation
Section 1.3

11. Non-competitive Inhibition
SBI 4U: Metablic Processes
Non-competitive Inhibition
Noncompetitive Inhibitors: substances that attach to the allosteric site and change the shape of the active site to prevent the substrate from binding to it.
Section 1.3

12. SBI 4U: Metablic Processes
Feedback Inhibition
When enzyme-catalyzed reactions occur in a sequence, feedback inhibition is when the product(s) of one reaction allosterically inhibits an enzyme of a previous reaction.
animation
Section 1.3

13. Inhibition by Location
SBI 4U: Metablic Processes
Inhibition by Location
Location: restricting the location of enzymes to certain locations within the cell helps to regulate activity
incorporation into specific organelle membranes or fluid-filled spaces (cytoplasm / inside organelles)
Section 1.3

14. Industrial Uses of Enzymes
SBI 4U: Metablic Processes
Industrial Uses of Enzymes
Section 1.3

15. Rate of Enzyme Activity
SBI 4U: Metablic Processes
Rate of Enzyme Activity
An increase in temperature increases the rate of reaction. However, when an enzyme is involved, if the temperature reaches beyond a critical point, denaturation may occur and since the enzyme is not functioning the reaction will slow down. (Body enzymes optimal: 37 degrees C)
Altering the pH may also alter the effectiveness of the enzyme, as most have an optimum pH (Ex. digestive enzymes)
Section 1.3

16. Rate of Enzyme Activity
SBI 4U: Metablic Processes
Rate of Enzyme Activity
Limiting Factor: The number of enzymes can be a limiting factor when the amount of substrate is increased, it takes time to catalyze a reaction; the enzymes become saturated.
Some enzymes need other components before they work properly:
Cofactors: nonprotein components that bind to the enzyme active site or the substrate to help the enzyme.
Coenzymes: these compounds often shuttle molecules from one enzyme to another.
Section 1.3