CU 0304 Enzymes

1. ENZYMES

2. Define the following terms:
1. Anabolic reactions: Reactions that build up molecules
2. Catabolic reactions: Reactions that break down molecules
Combination of anabolic and catabolic
3. Metabolism:
reactions
4. Catalyst: A substance that speeds up reactions
without changing the produced substances
5. Metabolic pathway: Sequence of enzyme controlled reactions
6. Specificity: Only able to catalyse specific reactions
7. Substrate: The molecule(s) the enzyme works on
8. Product: Molecule(s) produced by enzymes

3. Naming enzymes:
• Intracellular enzymes Work inside cells eg.DNA polymerase
• Extracellular enzymes Secreted by cells and work outside cells eg.
pepsin, amylase
• Recommended names Short name, often ending in ‘ase’ eg.
creatine kinase
• Systematic name Describes the type of reaction being
catalysed eg.
ATP:creatine phosphotransferase
• Classification number Eg. 2.7.3.2

4. Timeline of enzyme discovery
1835:
Breakdown of starch to sugar by malt
1877:
Name enzyme coined to describe chemicals in yeast that ferment sugars
1897:
Eduard Buchner extracted enzyme from yeast and showed it could work outside cells
1905:
Otto Rohm exyracted pancreatic proteases to supply enzymes for tanning
1926:
James B Sumner produced first pure crystalline enzyme (urease)
and showed enzymes were proteins
1930-1936:
Protein nature of enzymes finally established when digestive enzymes
crystallised by John H Northrop
1946: Sumner finally awarded Nobel prize

5. What Are Enzymes?
• Most enzymes are
Proteins (tertiary
and quaternary
structures)
• Act as Catalyst to
accelerates a
reaction
• Not permanently
changed in the
process
5

6. Enzymes are globular proteins
• Active site has a specific
shape due to tertiary
structure of protein.
• A change in shape of the
protein affects shape of
active site and the function
of the enzyme.

7. How do enzymes Work?
Enzymes work
by weakening
bonds which
lowers
activation
energy
7

8. Energy levels of molecules Enzymes lower the activation energy of a reaction
Activation energy
of uncatalysed
Initial energy state Activation energy reactions
of substrates of enzyme catalysed
reaction
Final energy state of
products
Progress of reaction (time)

9. Enzymes lower activation energy by forming an
enzyme/substrate complex
Substrate + Enzyme
Enzyme/substrate complex
Enzyme/product complex
Product + Enzyme

10. Lock and Key

11. Lock-and-key hypothesis assumes the active site
of an enzyme is rigid in its shape
How ever crystallographic studies indicate proteins are flexible.

12. Enzyme-Substrate
Complex
The substance
(reactant) an
enzyme acts on is
the substrate
Joins
Substrate Enzyme
12

13. In anabolic reactions
enzymes bring the substrate
molecules together.
In catabolic reactions the
enzyme active site affects
the bonds in substrates so
they are easier to break

14. Active Site
• A restricted region of an enzyme molecule which
binds to the substrate.
substrate
Active
Site
Substrate
Enzyme
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15. Induced Fit
• A change in
the shape of
an enzyme’s
active site
• Induced by
the substrate
15

16. Induced Fit
• A change in the configuration of
an enzyme’s active site (H+ and
ionic bonds are involved).
• Induced by the substrate.
Active Site
substrate
Enzyme
induced fit
16

17. Induced Fit

18. The Induced-fit hypothesis suggests the active site is
flexible and only assumes its catalytic conformation after
the substrate molecules bind to the site.
When the product leaves
the enzyme the active site
reverts to its inactive state.

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

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

21. Characteristics of enzymes
• Only change the rate of reaction. They do not change
the equilibrium or end products.
• Specific to one particular reaction
• Present in very small amounts due to high molecular
activity:
Turnover number = number of substrate molecules
transformed per minute by one enzyme molecule
Catalase turnover number = 6 x106/min

22. Enzymes in medicine
Glucose oxidase + peroxidase + blue dye on dipsticks to
detect glucose in urine:
Glucose oxidase
Glucose Hydrogen peroxide
peroxidase
Dye: Blue---Green---Brown
Dye changes according to
amount of glucose
Enzyme-linked immunosorbent assays (ELISAs)
detect antibodies to infections.

23. What Affects Enzyme
Activity?
• Three factors:
1. Environmental Conditions
2. Cofactors and Coenzymes
3. Enzyme Inhibitors
23

24. 1. Environmental Conditions
1. Extreme Temperature are the most
dangerous
- high temps may denature (unfold) the
enzyme.
2. pH (most like 6 - 8 pH near neutral)
3. Ionic concentration (salt ions)
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25. 2. Cofactors and Coenzymes
• Inorganic substances (zinc, iron) and
vitamins (respectively) are sometimes need
for proper enzymatic activity.
activity
• Example:
Iron must be present in the quaternary
structure - hemoglobin in order for it to pick
up oxygen.
25

26. Two examples of Enzyme
Inhibitors
a. Competitive inhibitors: are
chemicals that resemble an
enzyme’s normal substrate and
compete with it for the active
site.
site
Substrate
Enzyme
Competitive inhibitor
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27. Inhibitors
b. Noncompetitive inhibitors:
Inhibitors that do not enter the active site, but
site
bind to another part of the enzyme causing the
enzyme to change its shape, which in turn
shape
alters the active site.
site
Substrate Noncompetitive
Enzyme Inhibitor
active site
altered
27

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

29. 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.

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

31. Enzyme activity
Four Variables

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

33. Rate of Reaction
Temperature

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

35. 5- 40oC Temperature
Increase in Activity
40oC - denatures
Rate of Reaction
0 10 20 30 40 50 60
<5oC - inactive

36. 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

37. Effect of heat on enzyme activty
Denaturing the protein

38. 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

39. Rate of Reaction
pH

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

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

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

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

44. Enzyme Concentration
Rate of Reaction

45. Enzyme Concentration
Rate of Reaction
Enzyme Concentration

46. Substrate Concentration
Rate of Reaction

47. Substrate Concentration
Rate of Reaction
Substrate Concentration

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

49. How would you measure the effect of an enzyme?
• Compare uncatalysed rate with catalysed.
• Enzymes can increase rate by a factor of
between 108 to 1026

50. Characteristics of enzymes
• Rate of enzyme action is dependent on number of
substrate molecules present
Vmax = maximum rate of reaction
Rate of Reaction (M)
Vmax approached as all
active sites become
filled
Some active sites free
at lower substrate
concentrations
Substrate concentration

51. Why do scientists measure the initial rate of
reaction of enzyme-catalysed reactions?
Initial rate of reaction
Rate of Reaction (M)
They measure rate
at start of reaction
before any factors,
eg. substrate
concentration, have
had time to change.
Independent variable

52. Rate of enzyme –catalysed reactions are affected
by temperature.
Temperature coefficient Q10:
rate of reaction at (x + 10) oC
Q10 = -----------------------------------------
rate of reaction at x oC
Q10 for between 0 - 40 oC is 2

53. Enzymes denature at 60oC
Rate of reaction Optimum temperature
Rate doubles Enzyme denaturing and
every 10oC losing catalytic abilities
Temperature
Some thermophilic bacteria have enzymes with optimum
temperatures of 85oC

54. pH affects the formation of hydrogen bonds and
sulphur bridges in proteins and so affects shape.
trypsin cholinesterase
pepsin
Rate of Reaction (M)
2 4 6 8 10
pH