1. ENZYMES

2. 10
Enzymes
-Enzymes are proteins that function as biological catalysts
-Catalyst: a substance that speeds up a chemical reaction
and is not changed by the reaction.
They are present in the cytoplasm of all cells
There are hundreds of different enzymes but each enzyme
speeds up only one kind of reaction. They are specific.
For example, glucose and fructose might join up slowly to
form sucrose
glucose- -fructose
With the right enzyme present, the reaction happens faster
glucose- -fructose

3. 12
The substrate molecules fit the shape of the enzyme
enzyme
substrate A
substrate B

4. 13

5. 14
substrates combine temporarily with enzyme
enzyme joins substrates together

6. 15
enzyme unchanged new compound released
and ready for by enzyme
next reaction

7. 16
Different types of enzyme reaction
The last 4 slides show how an enzyme is involved in
combining substrates to create a larger molecule
For example, the enzyme could be building up a sucrose
molecule from glucose and fructose (anabolic reaction)
The next sequence shows how an enzyme can help to
break a large molecule into smaller molecules (catabolic
reaction)
For example an enzyme can split a sucrose molecule
into the smaller glucose and fructose molecules

8. 17
A ‘breaking-down’ reaction
the shape of the substrate molecule
fits the enzyme shape
this is called
the active site
of the enzyme

9. 18
Intermediate stage (1)
substrate combines
temporarily with enzyme
enzyme will break
molecule here

10. 19
Intermediate stage (2)
substrate splits and
separates from enzyme

11. 20
Final break-down products
enzyme ready for
next reaction
end-products

12. 21
Properties of enzymes
-Enzymes can act on only one type of substrate (specific)
-They always produce the same end products
-Although they take part in the reaction, they are not used up
-Because enzymes are proteins, they are denatured by heat
or some chemicals
Denaturing involves a change of shape in the enzyme
molecule so that it cannot combine with the substrate
Individual enzymes work best at a particular temperature
and pH (acidity or alkalinity)

13. 22
Enzymes can act on only one type of substrate
this substrate cannot combine
with this enzyme
this substrate cannot combine
with this enzyme

14. Because enzymes are proteins, they are denatured by 23
heat or some chemicals
enzyme
enzyme +
denatured
substrate
by heat
denatured enzyme cannot combine with substrate

15. ENZYME ACTION 24
1
E
1. A glucose molecule combines with
glucose
the active site on an enzyme
molecules

16. ENZYME ACTION 24
1
E
1. A glucose molecule combines with
glucose
the active site on an enzyme
molecules

17. 25
E
2 A region of the active site is still available

18. 26
3 One end of a growing starch
molecule combines with the
glucose molecule at the active
part of starch
site molecule
E

19. 27
4 The growing starch molecule breaks
free from the enzyme which is now free
to repeat the reaction
E

20. 28
Enzyme action
11 2
E E part of starch
molecule
glucose
E 3
molecules E
E E 4

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

22. 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.

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

24. Enzyme activity
Four Variables

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

26. Rate of Reaction
Temperature

27. Temperature
Rate of Reaction
0 10 20 30 40 50 60

28. 5- 40oC Temperature
Increase in Activity
40oC - denatures
Rate of Reaction
0 10 20 30 40 50 60
<5oC - inactive

29. 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

30. Effect of heat on enzyme activty
Denaturing the protein

31. ph
• The ph scale measures how acidic or alkaline a
substance is.
• The chemical properties of many solutions enable
them to be divided into 3 categories:
1) Neutral: solutions with a ph of 7.
2) Alkaline: solutions with a ph greater than 7
3) Acidic: solutions with a ph less than 7.

32. Ph scale

33. Rate of Reaction
pH

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

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

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

37. pH
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

38. Enzyme Concentration
Rate of Reaction

39. Enzyme Concentration
Rate of Reaction
Enzyme Concentration

40. Substrate Concentration
Rate of Reaction

41. Substrate Concentration
Rate of Reaction
Substrate Concentration

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

43. 37
Question 1
Enzymes are
(a) proteins
(b) lipids
(c) carbohydrates
(d) a combination of these

44. 38
Question 2
An enzyme can
(a) change a reaction
(b) prevent a reaction
(c) slow down a reaction
(d) speed up a reaction

45. 39
Question 3
A substrate is a substance which
(a) an enzyme acts on
(b) is produced by an enzyme reaction
(c) is a particular kind of enzyme
(d) is any chemical substance in a cell

46. 40
Question 4
An enzyme can
(a) combine with different substrates
(b) form different kinds of end-product
(c) function at temperatures above 90oC
(d) speed up a reaction in the cytoplasm

47. 41
Question 5
The part of an enzyme which combines with the substrate
is called
(a) the reaction centre
(b) the active site
(c) the action centre
(d) the reaction site

48. 42
Question 6
After being exposed to a high temperature an enzyme
cannot function because
(a) it has been broken down
(b) its shape has been changed
(c) its composition has been changed
(d) it cannot separate from its substrate