1. Pages 32-33 Specification area 3.1.4.2
Enzyme inhibition
Pages 32-33
Specification area

2. Specification

3. Objectives Describe the nature of enzyme inhibition
Explain how competitive inhibitors affect the active site
Explain how non-competitive inhibitors affect the active site
Explain control of metabolic pathways

4. Enzyme Inhibitors Enzymes can be deactivated by enzyme inhibitors.
Many drug molecules are enzyme inhibitors.
Native arsenic
Mercury
Photo: US EPA
Some heavy metals (above) are examples of poisons which act as irreversible enzyme inhibitors.

5. Objective 1 Describe the nature of enzyme inhibition
Name the 2 types of inhibitor
What is affected by an inhibitor which affects the active site?

6. Enzyme inhibitors: mode of action

7. Objective 2 Explain how competitive inhibitors affect the active site
Where do they bind?
What effect do they have on the active site?
Can the effect of this inhibitor be reduced in any way?

8. Objective 2 Explain how competitive inhibitors affect the active site
Where do they bind?
What effect do they have on the active site?
Can the effect of this inhibitor be reduced in any way?
Active site
Occupy the active site preventing the formation of enzyme substrate complexes
Increase the concentration of substrate

9. What effect do they have on the active site?
Objective 3 Explain how non-competitive inhibitors affect the active site
Where do they bind?
What effect do they have on the active site?
Can the effect of this inhibitor be reduced in any way?

10. Objective 3 Explain how non-competitive inhibitors affect the active site
Where do they bind?
What effect do they have on the active site?
Can the effect of this inhibitor be reduced in any way?
Allosteric site NOT THE ACTIVE SITE
Change its shape so it is no longer complementary to the substrate
NO – the number of inhibitor molecules will each affect an enzyme

11. Comparing competitive and non-competitive inhibitors

12. Compare and contrast Competitive Non-competitive
Inhibitor has similar shape to substrate
Binds to active site
Does not alter enzyme shape
Inhibitor and substrate compete for active site
Level of inhibition reduced as substrate concentration increased
At high substrate concentration inhibitor has little effect

13. Compare and contrast Competitive Non-competitive
Inhibitor has similar shape to substrate
Does not
Binds to active site
Binds at a different site
Does not alter enzyme shape
Active site shape changed
Inhibitor and substrate compete for active site
Inhibitor does not enter active site
Level of inhibition reduced as substrate concentration increased
Inhibition level unchanged by adding more substrate
At high substrate concentration inhibitor has little effect
Inhibitor has same effect as it changes the enzyme

14. Objective 4 Explain control of metabolic pathways

15. End-product inhibition
Enzyme inhibition is important in regulating metabolic pathways. The final (end) product often acts as a regulator of the pathway in a process called end-product inhibition.
When the amount of end product is high, it binds non-competitively to an enzyme in the pathway, blocking further production of itself.
When the amount of end product falls, inhibition ends and the pathway restarts.
Teacher notes
End-product inhibition is an example of negative feedback.
The synthesis of ATP is regulated in this way, with ATP acting as the inhibitor.

16. End product inhibition
Select feedback
inhibition
Metabolic pathways are sequences of chemical reactions
each controlled by a different enzyme
INHIBITS
enzyme 1 2 3 4 A B C D E
The initial
substrate
is converted by a series of
intermediate compounds
into the
final product
If E builds up it is wasteful to the cell
As E builds up it inhibits enzyme 1 so halting further production
usually by reversible non-competitive inhibition
Further production of the end product is prevented

17. Homework Summary questions p33 Control of metabolic pathways p33
Practice questions pp34-5
Revise for end of topic test

18. Assessment
Self Test next week (teacher)

19. Extension activity - Student models
3 people need to be a competitive inhibitor
One needs to be a non-competitive inhibitor
6 people need to be substrates
6 people need to form an enzyme molecule
Your teacher will instruct you on what to do

20. Keywords
Competitive, non-competitive, inhibitor, active site