1. ENZYMES

2. Outline Review – What is an enzyme? Models of enzyme activity
Lock and key
Induced fit model
Factors affecting enzyme activity
Temperature pH
Regulation of enzyme activity
Inhibition
Allosterically
Feedback inhibition

3. “Biological catalysts”: Speed up reactions in the body
What is an enzyme?
“Biological catalysts”: Speed up reactions in the body

4. What is a catalyst????
a substance which increase in the rate of a chemical reaction due to it’s participation.
The effect of a catalyst may vary due to the presence of other substances known as inhibitors or poisons (which reduce the catalytic activity)
Promoters (which increase the activity).
The opposite of a catalyst, a substance that reduces the rate of a reaction, is an inhibitor.

5. The antonym…
The opposite of a catalyst, a substance that reduces the rate of a reaction, is an inhibitor.

6. Literacy T.Y.P minutes.
List three synonyms and three antonyms of a catalyst.
Give an example of each.
Share with your peers.

7. Often globular (spherical) in shape
Type of protein
Polymer of amino acids
Often globular (spherical) in shape
Contain “active sites” – depressions or grooves on the surface where molecules can bind

8. Binding to an enzyme is very selective:
Active sites interact with specific molecules to catalyze specific reactions
The molecule that binds to an enzyme is called its “substrate”

9. Enzymes lower the activation energy required for a reaction to occur.
Stabilizes the transition state by stretching the bonds of the substrate

10. Some enzymes need to bind to additional molecules to function:
Cofactors (usu. metal ions), or
Coenzymes (act like shuttles btw. enzymes)
Apoenzyme – The enzyme, without its cofactors/coenzymes
Holoenzyme – The active form, bound to cofactors/coenzymes

11. MODELS OF ENZYME ACTIVITY
Lock and Key model
Induced fit model

12. The “Lock and Key” model
The enzyme has an active site that is unchanging
Substrates bind  chemical process occurs

13. Induced fit model The enzyme can change its shape
One substrate molecule binds weakly
The enzyme’s active site changes shape so that a second substrate molecule can bind
The second substrate binds  Chemical process (rx) occurs

15. FACTORS AFFECTING ENZYME ACTIVITY
Temperature pH

16. Temperature

17. Too much heat will disrupt the 2° , 3° and 4° structure
Increase in activity with temperature (molecules have more energy) but only to a certain point.
Too much heat will disrupt the 2° , 3° and 4° structure
Denaturation & loss of function

19. Every enzyme has a temperature at which it functions best – this is the optimal temperature
For human enzymes it is usually 37°C (body temp.)

21. pH Enzymes also have optimal pHs
These will vary according to the location in which they function
Location
Optimal pH
Pepsin
Stomach 2
Trypsin
Small intestine 8

23. REGULATION OF ENZYME ACTIVITY
Inhibition
Allosterically
Feedback inhibition

24. Competitive inhibition
Are very similar in shape to an enzyme’s substrate.
Bind to the active site, and physically block the correct substrate from binding.

25. Competitive Inhibition

26. Enzyme Efficiency / Rate of Rx

27. Noncompetitive inhibition
May be allosteric OR
The inhibitor directly affects the enzyme so that it cannot carry out its function. (chemicals that alter the enzyme’s shape and therefore function)

28. Noncompetitive inhibition

29. Noncompetitive inhibition

30. Comparing the 2 inhibitions

31. Allosteric Regulation
Allosteric site – Site on an enzyme that can bind with an effector.
NOT the same as active site.
Effector:
Activator, or
Inhibitor

32. Inhibition vs Activation Inhibitors vs Activators
Some substances can inhibit enzyme function – Inhibitors
Some substances can enhance enzyme function – activators
Inhibition can be either competitive or noncompetitive

33. Allosteric activator Allosteric inhibitor Stabilize the active-form
Stabilize the inactive form
See pg. 73, Figure 7

34. Feedback inhibition Often biological reactions occur in a series.
Feedback inhibition: The product of a series of enzyme-catalyzed reactions acts to allosterically inhibit an enzyme that acts earlier in the series.

35. WHY IS FEEDBACK INHIBITION important?
5 minutes discussions:
WHY DO CELLS NEED FEEDBACK?
WHY DO YOU NEED FEEDBACK?
“TWO-WAY” WORLD
ANYONE?

36. SOME APPLICATIONS
Cheese-making
Cow enzyme rennet

37. Insulin for Type 1 diabetics

38. Lactase to digest lactose

39. There are three main enzymes found in a human body
digestive enzymes
metabolic enzymes
food enzymes

40. Who’s ‘ase is it anyways?
Naming enzymes most end in “ase”