1. BIOLOGY 12
Enzymes

2. Enzymes
Video
Enzyme Basics

3. Like all catalysts, enzymes work by lowering the activation energy for a reaction, thus dramatically increasing the rate of the reaction. As a result, products are formed faster and reactions reach their equilibrium state more rapidly. Most enzyme reaction rates are millions of times faster than those of comparable un-catalyzed reactions. As with all catalysts, enzymes are not consumed by the reactions they catalyze, nor do they alter the equilibrium of these reactions.

4. Enzymes proteins catalysts for biological reactions substrate specific
they initiate chemical reactions without being used in the reaction (reusable)
usually named after their substrate, most end in “ase” (ex. Maltase)
“Lock and Key” Fit  Induced Fit Model

5. Enzymes
they lower the activation energy, therefore increase the rate of reaction

6. Enzymes activity is lost if they are denatured
the unfolding and inactivation – by heating or chemical denaturants, which disrupt the three-dimensional structure of the protein

7. Enzymes
How Enzymes Work

8. Enzyme Action Lock and Key Model
substrate binds to active site of enzyme
enzyme-substrate complex forms
substrate reacts and product is formed
product is released (enzyme is unchanged by reaction)

9. Enzyme Action

10. Enzyme Action Induced Fit Model
scientists have modified the “lock and key” model
enzyme structure is flexible – not rigid
the shape of the enzyme’s active site and the shape of the substrate do not need to match exactly

11. Enzyme Action
when the enzyme and substrate join, the enzyme changes its shape slightly (adjusts to fit)
this increases the range of substrate specificity

12. Enzyme Action

13. Catalytic Cycle of an Enzyme

14. Activation Energy (EA)
the minimum amount of energy required to start a chemical reaction
examples:
Oxygen gas + Hydrogen gas + Heat (A.E) = Water
Wood + Oxygen + Burning Match (A.E) = Burning wood

15. Activation Energy (EA)
enzymes use a variety of mechanisms that lower activation energy and speed up a reaction
*see graphs on page 69
Activation Energy Graph

16. example of why we have enzymes:
enzymes allow reactions to take place at lower temperature (i.e. body temperature)
the reactions of living organisms cannot depend on heat as a source of activation energy
high temperatures would destroy cells
heat would be far too random of a source of activation energy (not dependable)
cells must carry out specific reactions at definite times

17. Recap on Enzymes
each is specific – guides only one type of cell reaction
they are not permanently changed or used up during a reaction
can be used over and over again
the shape of the enzyme is crucial to the reaction

18. Factors Affecting Enzyme Activity
environmental factors
cofactors and coenzymes
enzyme inhibitors

19. Factors Affecting Enzyme Activity
temperature
up to a point, the speed of the reaction increases with the increase in temperature
most enzymes function optimally around body temperature (between 35o – 40oC)
extreme temperatures can denature an enzyme

20. Factors Affecting Enzyme ActivitypH
the optimal pH is between 6 and 8 (near neutral)

21. Factors Affecting Enzyme Activity
cofactors
inorganic non-protein helpers are sometimes needed for optimal enzyme activity
examples:
vitamins
zinc
iron must be present in the quaternary structure of hemoglobin in order for it to pick up oxygen

22. Factors Affecting Enzyme Activity
enzyme inhibitors
competitive:
has a structure similar to the substrate
competes with the substrate for the active site
occupies the active site

23. Factors Affecting Enzyme Activity
enzyme inhibitors
non-competitive:
does not have a structure like the substrate
binds to the enzyme but not active site
changes the shape of enzyme and active site
substrate cannot fit into altered active site
no reaction occurs

24. Factors Affecting Enzyme Activity

25. Factors Affecting Enzyme Activity
How Enzymes Work

26. Lets Label It

27. Questions
You turn on a battery powered tape deck and the reels in the cassette begin to rotate.
How does this example explain energy transformation?
A. Potential energy (stored energy) in the batteries was converted to kinetic energy (mechanical energy).

28. Questions
Suppose you started a fire by using a magnifying glass to focus the sun’s image on some paper.
What is the source of activation energy for this reaction?
A. The concentrated sunlight was absorbed and changed to heat. This heat provided the activation energy.

29. Questions
Explain how the enzyme maltase can control a reaction involving maltose, but not one involving sucrose.
Maltose consists of two bonded glucose units, whereas sucrose consists of a glucose bonded to a fructose.
If the active site of the enzyme maltase fits with maltose, it will not fit with sucrose.

30. Compare and Contrast Kinetic Energy / Potential Energy
Endergonic / Exergonic
Enzyme/ Substrate
Lock and Key Model / Induced Fit Model
Enzyme / Coenzyme
Competitive Inhibitors / Non-Competitive Inhibitors

31. Questions
Page 77 #1, 4, 5, 6, 7, and 8.