1. Enzyme Action Learning objective: to describe different models for
enzyme action and to investigate factors which control the
rate of an enzyme reaction

2. Lock and Key

3. Lock and Key
However certain substances can bind to the enzyme at sites other than the
Active site and modify its activity (inhibitors/co-factors)
Idea that the enzyme is flexible

4. Induced Fit

5. Enzyme reactions
enzyme + substrate
enzyme-substrate complex

6. Enzyme reactions
enzyme + substrate
enzyme-substrate complex
E +S ES

7. Enzyme reactions enzyme + substrate enzyme-substrate complex E +S ES
enzyme + product
enzyme-substrate complex ES
E +P

8. How fast an enzyme is working
Enzyme activity
How fast an enzyme is working
Rate of Reaction

9. How fast an enzyme is working
Enzyme activity
How fast an enzyme is working
Rate of Reaction
Rate of Reaction = Amount of substrate changed (or amount product formed)
in a given period of time.

10. Enzyme activity
Rate of Reaction
Variable you are looking at

11. Enzyme activity
Four Variables

12. Enzyme activity Temperature pH Enzyme Concentration
Four Variables
Enzyme Concentration
Substrate Concentration

13. Temperature
Rate of Reaction

14. Temperature
Rate of Reaction 10 20 30 40 50 60

15. Temperature 5- 40oC Increase in Activity 40oC - denatures
Rate of Reaction 10 20 30 40 50 60
<5oC - inactive

16. Effect of heat on enzyme activty
If you heat the protein above its optimal temperature
bonds break
meaning the protein loses it secondary and tertiary structure

17. Effect of heat on enzyme activty
Denaturing the protein

18. Effect of heat on enzyme activty
Denaturing the protein
ACTIVE SITE CHANGES SHAPE
SO SUBSTRATE NO LONGER FITS
Even if temperature lowered – enzyme can’t regain its correct shape

19. pH
Rate of Reaction

20. pH
Rate of Reaction 1 2 3 4 5 6 7 8 9

21. pH
Narrow pH optima
Rate of Reaction 1 2 3 4 5 6 7 8 9

22. pH
Narrow pH optima
WHY?
Rate of Reaction 1 2 3 4 5 6 7 8 9

23. Effect charged residues at activepH
Narrow pH optima
Disrupt Ionic bonds - Structure
Rate of Reaction
Effect charged residues at active
site 1 2 3 4 5 6 7 8 9

24. Enzyme Concentration
Rate of Reaction

25. Enzyme Concentration
Rate of Reaction
Enzyme Concentration

26. Substrate Concentration
Rate of Reaction

27. Substrate Concentration
Rate of Reaction
Substrate Concentration

28. Substrate Concentration
Active sites full- maximum turnover
Rate of Reaction
Substrate Concentration