1. Factors Affecting Enzyme Activity

2. Learning Outcomes
apply knowledge of proteins to explain the effects on enzyme activity of: pH
temperature
substrate concentration
enzyme concentration
competitive inhibitors, and non-competitive inhibitors including heavy metals
differentiate between the roles of enzymes and coenzymes in biochemical reactions
identify the role of vitamins as coenzymes

3. Factors affecting enzyme activity
Temperature pH
Concentration
Activation
Inhibitors
Co-enzymes

4. What happens to the rate of most chemical reactions as the temperature is increased?
Why?

5. Temperature All enzymes have an optimal temperature
Up to this temperature, the reaction rate increases as temperature increases
Above this temperature, denaturation of the enzyme occurs (irreversible)

6. What would you expect to be the optimal temperature of enzymes that function in the human body?

7. Effect of temperature on enzyme activity
Optimal temperature
Enzyme activity
Temperature

8. How might a strong acid or base affect a protein?

9. pH All enzymes have an optimal pH
High or low pH causes reduced enzyme activity and denaturation of the enzyme

10. Effect of pH on enzyme activity
Optimal pH
Enzyme activity pH

11. Fig. 6.8

12. What happens if we increase or decrease the concentration of substrate?

13. Substrate concentration
Increasing the substrate concentration increases the reaction rate
only to the point where all enzymes are being used

14. Effect of substrate concentration
Enzyme activity
Substrate concentration

15. What if we add more enzyme?
How would this happen in the body?

16. Enzyme concentration
In cells, enzyme concentration is genetically controlled (control of protein synthesis)
Increasing the amount of enzyme will increase the reaction rate (as long as substrate is present)

17. Effect of enzyme concentration
Enzyme activity
Enzyme concentration

18. Activation
Enzymes may be “turned on” by the presence of another molecule (ex. The addition of a phosphate group, known as phosphorylation)

19. Enzyme activation

20. How could you prevent a substrate from binding to an enzyme active site?
Would this ever be a desirable outcome?

21. Inhibition
Inhibitors are molecules other than the substrate that bind to the enzyme and inhibit its activity

22. Competitive inhibition
Competitive inhibitors compete with the substrate by binding to the active site

23. Non-competitive inhibition
Non-competitive inhibitors bind to a different site on the enzyme (allosteric site)
Change the shape of the enzyme’s active site

24. Toxic heavy metals such as lead, cadmium and mercury can bind to enzymes causing denaturation
Act as non-competitive inhibitors

25. Feedback inhibition
Sometimes the product of the pathway acts as an inhibitor
This stops the pathway when there is enough of the product

26. Fig. 6.9a

27. Fig. 6.9b

28. Enzyme cofactors
Cofactors or coenzymes are non-protein molecules that assist the enzyme
May be inorganic ions ex. Copper, zinc, or iron
Often are organic molecules derived from vitamins
Function is often to transfer electrons or functional groups (ex. Phosphate) to the substrate

29. Vitamin deficiency results in interference with enzyme activity in various metabolic pathways
(so eat your veggies!)