1
Think about…
4.1 Metabolism
4.2 Properties and actions of
enzymes
4.3 Factors affecting the rate of
enzymatic reactions
4.4 Applications of enzymes
Recall ‘Think about…’
Summary concept map
2
I can help you!
3
Wash jeans with
stones.
Stones break some
cellulose fibres &
remove the blue
dye.
4
enzyme
Now we can use
enzymes to break
down the fibres
more quickly!
5
1
What are enzymes
enzyme
6
2
What are the
importance of enzymes
to organisms
enzyme
7
3
enzyme
What are the
advantages of using
enzymes in the making
of stonewashed jeans
8
4.1 Metabolism
• different chemical reactions take place
in living cells
respiration
protein
synthesis
lipid
synthesis
9
4.1 Metabolism
• different chemical reactions take place
in living cells
sum of the chemical
reactions that take place in an
organism
= metabolism (新陳代謝)
10
4.1 Metabolism
Metabolism
Catabolism
(分解代謝)
Anabolism
(合成代謝)
11
4.1 Metabolism
1 Catabolism
complex
molecule
energy
simple
molecules
• breaking-down reactions
• release of energy
12
4.1 Metabolism
1 Catabolism
• example: respiration
carbon
water +
dioxide
glucose
energy
13
4.1 Metabolism
Metabolism
Catabolism
(分解代謝)
Anabolism
(合成代謝)
14
4.1 Metabolism
2 Anabolism
simple
molecules
energy
• building-up reactions
• requires energy
complex
molecule
15
4.1 Metabolism
2 Anabolism
• example: condensation of glucose
starch
glucose
energy
16
4.1 Metabolism
What are catabolism, anabolism
and metabolism?
Catabolism all breaking-down
reactions in an organism
Anabolism all building-up reactions
in an organism
Metabolism all chemical reactions in
an organism
17
4.2 Properties and actions of
enzymes
What is the role of
enzymes in metabolism?
18
4.2 Properties and actions of
enzymes
reacting
molecules

product
(生成物)
energy barrier
(能障)
19
4.2 Properties and actions of
enzymes
energy
reacting
molecules
product
(生成物)
Energy supplied
energy to
barrier
overcome the
energy barrier(能障)
20
4.2 Properties and actions of enzymes
• analogy: pushing a rock up a hill
reacting
molecule
product
21
4.2 Properties and actions of enzymes
• analogy: pushing a rock up a hill
reacting
molecule
energy barrier
product
- the reaction does not start due to
the presence of energy barrier
22
4.2 Properties and actions of enzymes
• analogy: pushing a rock up a hill
maximum energy
energy
- when energy is supplied …
reaction starts
23
4.2 Properties and actions of enzymes
How can the energy barrier be
overcome in our body?
24
4.2 Properties and actions of enzymes
By increasing the temperature?
smaller
energy barrier
• energy level raised
energy barrier is easier to overcome
25
4.2 Properties and actions of enzymes
By increasing the temperature?
Not possible
smaller
energy
because
highbarrier
temperature
kill the body cells!
• energy level raised
energy barrier is easier to overcome
26
4.2 Properties and actions of enzymes
lower
energy barrier
• rate of chemical reactions is speeded up
by enzymes (酶)
27
4.2 Properties and actions of enzymes
energy
• rate of chemical reactions is speeded up
by enzymes (酶)
28
4.2 Properties and actions of enzymes
4.1
Demonstration of the breaking-down
action of enzymes
1 Prepare liver extract.
a Grind fresh liver with cold distilled water.
cold distilled
water
fresh pig
liver
29
4.2 Properties and actions of enzymes
4.1
b Filter the ground
tissue with filter
paper.
filter paper
liver extract
30
4.2 Properties and actions of enzymes
4.1
c Dilute the liver extract by 50% with cold
distilled water.
distilled water
liver extract
31
4.2 Properties and actions of enzymes
4.1
2 Set up 3 test tubes A to C. Observe for the
release of gas and the gas given off with a
glowing splint.
A
hydrogen
peroxide
+ liver
extract
B
distilled
water +
liver
extract
C
hydrogen
peroxide +
distilled
water
32
4.2 Properties and actions of enzymes
4.1
Results and discussion
• A gas is released from tube A.
The gas is oxygen because
it re-lights a glowing splint.
• No oxygen is released from
the control set-ups (tubes B
and C).
33
4.2 Properties and actions of enzymes
4.1
Results and discussion
• Fresh liver tissues can break down
hydrogen peroxide possibly due to the
presence of catalase in the liver tissue.
• Catalase speeds up the breakdown of
hydrogen peroxide.
34
4.2 Properties and actions of enzymes
How do enzymes work?
• each enzyme has an active site of a
specific (專一的) shape
active site (活性部位)
enzyme
35
4.2 Properties and actions of enzymes
How do enzymes work?
• active site can combine with substrate
(受質) molecule(s)
substrate
enzyme
shapes fit
together!
36
4.2 Properties and actions of enzymes
How do enzymes work?
• active site can combine with substrate
(受質) molecule(s)
substrate
enzyme
enzymesubstrate
complex
(酶受質複合物)
• complex breaks down to give product(s)
37
4.2 Properties and actions of enzymes
How do enzymes work?
• in catabolic reactions:
substrate
enzymesubstrate
complex
enzyme
38
4.2 Properties and actions of enzymes
How do enzymes work?
• in catabolic reactions:
products
enzymesubstrate
complex
enzyme unchanged and can be reused
39
4.2 Properties and actions of enzymes
How do enzymes work?
• in anabolic reactions:
substrates
enzymesubstrate
complex
enzyme
40
4.2 Properties and actions of enzymes
How do enzymes work?
• in anabolic reactions:
product
enzymesubstrate
complex
enzyme unchanged and can be reused
41
4.2 Properties and actions of enzymes
Properties of enzymes
1) Biological catalysts
• act as catalysts (催化劑) in organisms
speed up metabolic reactions
42
4.2 Properties and actions of enzymes
Properties of enzymes
2) Reusable
• enzyme returns to its original form
after reaction
before
reaction
same!
after
reaction
43
4.2 Properties and actions of enzymes
Properties of enzymes
3) Required in small amount
large amount of products produced
reusable
reusable
reusable
44
4.2 Properties and actions of enzymes
Properties of enzymes
4) Proteins
• enzymes are denatured (變性) at
high temperatures and extreme pH
45
4.2 Properties and actions of enzymes
Properties of enzymes
5) Specific action
different shape!
46
4.2 Properties and actions of enzymes
Properties of enzymes
5) Specific action
• each enzyme combines with a specific
substrate
each enzyme catalyses only one
type of reaction
47
4.2 Properties and actions of enzymes
Properties of enzymes
5) Specific action
• can be explained by
lock-and-key
hypothesis
(鎖鑰假說)
48
4.2 Properties and actions of enzymes
Lock-and-key hypothesis
specific
shape
• fit only a particular lock
49
4.2 Properties and actions of enzymes
Lock-and-key hypothesis
active sites of
specific shape
• fit only a particular substrate
50
4.2 Properties and actions of enzymes
1 Enzymes are biological catalysts
that speed up chemical reactions
in organisms by lowering the
energy barrier of reactions.
They are important in regulating
metabolism.
51
4.2 Properties and actions of enzymes
2
An enzyme works when its
active site combines with
substrate(s) to form an
enzyme-substrate complex . The
complex then breaks down to give
the product(s). The enzyme is
released in its original form .
52
4.2 Properties and actions of enzymes
3 Enzyme actions are specific
because their active sites have
specific shapes . Enzyme
combines only with substrate(s) that
fits into its active site. The specificity
of enzyme actions can be explained
by the lock-and-key hypothesis .
53
4.2 Properties and actions of enzymes
4 Five properties of enzymes:
i) They are biological catalysts .
ii) They can be reused .
iii) They are required in small
amount.
iv) They are proteins .
v) Their actions are specific .
54
4.3 Factors affecting the rate
of enzymatic reactions
Enzyme activity
• reaction rate of an enzymatic
reaction
= the rate at which substrates are
used up or broken down
= the rate of product formation
55
4.3 Factors affecting the rate
of enzymatic reactions
Enzyme
activity
enzyme
• reaction rate of an enzymatic
reaction
= the rate at which substrates are
used up or broken down
= the rate of product formation
56
4.3 Factors affecting the rate
of enzymatic reactions
enzyme
temperature
pH
inhibitor
57
4.3 Factors affecting the rate of enzymatic reactions
Temperature
reaction rate
0˚C
low kinetic energy
enzyme inactive
temperature(℃)
0
10
20
30
40
50
60
58
4.3 Factors affecting the rate of enzymatic reactions
Temperature
reaction rate
temperature rises
more kinetic energy
temperature(℃)
0
10
20
30
40
50
60
59
4.3 Factors affecting the rate of enzymatic reactions
Temperature
more kinetic energy
molecules vibrate more
rapidly
collide more frequently
have higher chance to
form an enzymesubstrate complex
60
4.3 Factors affecting the rate of enzymatic reactions
Temperature
reaction rate
temperature rises
0
10
20
more kinetic energy
reaction rate
increases
temperature(℃)
30 40 50 60
61
4.3 Factors affecting the rate of enzymatic reactions
Temperature
reaction rate
maximum rate
optimum temperature
rate of enzymatic
reaction reaches
maximum
temperature(℃)
0 10 20 30 40 50 60
62
4.3 Factors affecting the rate of enzymatic reactions
Temperature
reaction rate
temperature higher
than optimum
temperature
enzyme denatured
reaction rate
decreases
temperature(℃)
0 10 20 30 40 50 60
63
4.3 Factors affecting the rate of enzymatic reactions
Enzymes are killed
by heating so the
rate of enzymatic
reaction decreases.
64
4.3 Factors affecting the rate of enzymatic reactions
Enzymes are NOT living things.
They cannot be killed. They
are denatured (their shapes
are changed) at very high
temperatures.
65
4.3 Factors affecting the rate of enzymatic reactions
4.2
Simulation
Investigation of the effect of
temperature on enzyme activity
1 Add amylase solution to test tubes A to F.
Add starch solution to test tubes 1 to 6.
2 Leave the different pairs of test tubes in
water baths at different temperatures for
10 minutes.
66
4.3 Factors affecting the rate of enzymatic reactions
4.2
ice
starch solution
0˚C 20˚C 40˚C 60˚C 80˚C 100˚C
amylase solution
67
4.3 Factors affecting the rate of enzymatic reactions
4.2
3 Pour the amylase solution into starch
solution. Put the tube of mixture back to
its beaker. Record the time as zero.
amylase solution
starch solution
68
4.3 Factors affecting the rate of enzymatic reactions
4.2
4 At 2-minute intervals, transfer a drop of
each mixture to an iodine drop. Record
the time it takes for the blue-black colour
to disappear.
amylase
and starch
mixture
iodine drops
spot plate
69
4.3 Factors affecting the rate of enzymatic reactions
4.2
Results and discussion
• The time it takes for the blue-black colour
to disappear is the shortest at 60˚C.
• The starch does not disappear at 0˚C, 80˚C
and 100˚C.
70
4.3 Factors affecting the rate of enzymatic reactions
4.2
Results and discussion
• At low temperature, the enzymatic reaction
rate is low because amylase is inactive.
• Its activity increases with temperature until
it reaches a maximum (around 60˚C).
71
4.3 Factors affecting the rate of enzymatic reactions
4.2
Results and discussion
• The enzyme activity is the highest at 60˚C.
• Above the optimum temperature, the
enzyme activity decreases and the reaction
rate decreases until the enzyme becomes
denatured and can no longer work.
72
4.3 Factors affecting the rate
of enzymatic reactions
enzyme
temperature
pH
inhibitor
73
4.3 Factors affecting the rate of enzymatic reactions
pH
reaction rate
pepsin
many enzymes in
mammals (e.g.
salivary amylase)
pancreatic
lipase
74
2
4
6
8
10 12 14 pH
4.3 Factors affecting the rate of enzymatic reactions
pH
reaction rate
each enzyme
works in a narrow
range of pH
75
2
4
6
8
10 12 14 pH
4.3 Factors affecting the rate of enzymatic reactions
pH
optimum pH for
most enzymes:
pH 5 – pH 9
each enzyme
have their own
optimum pH
unsuitable pH
causes
denaturation
reaction rate
76
2
4
6
8
10 12 14 pH
4.3 Factors affecting the rate of enzymatic reactions
4.3
Simulation
Investigation of the effect of pH on
enzyme activity
1 Add Benedict’s solution to test tubes 1 to 6.
Benedict’s
solution
77
4.3 Factors affecting the rate of enzymatic reactions
4.3
2 Add sucrose solution to another 6 test
tubes A to F. Then add citrate-phosphate
buffer solution at different pH values to
the tubes as shown.
Tube
pH of buffer
solution
A
B
C
D
E
F
3.2 4.0 5.2 6.0 7.0 8.0
78
4.3 Factors affecting the rate of enzymatic reactions
4.3
3 Add invertase solution to test tubes A to F.
Leave at room temperature for 5 minutes.
sucrose solution
+ citratephosphate buffer
+ invertase
79
4.3 Factors affecting the rate of enzymatic reactions
4.3
4 Pour the Benedict’s solution in test tubes 1 to
6 into test tubes A to F respectively. Shake the
tubes gently. Put the test tubes into a boiling
water bath for 10 minutes.
boiling water
80
4.3 Factors affecting the rate of enzymatic reactions
4.3
5 Allow the tubes to stand for 15 minutes.
Measure the depth of any brick-red
precipitate settled in the test tubes.
81
4.3 Factors affecting the rate of enzymatic reactions
4.3
Results and discussion
• Precipitate is formed in tubes A, B, C and
D. The largest amount of precipitate is
settled in tube C. No precipitate is formed
in tubes E and F.
• The results show that invertase works in an
acidic medium. It has an optimum pH
value around pH 5.2.
82
4.3 Factors affecting the rate
of enzymatic reactions
enzyme
temperature
pH
inhibitor
83
4.3 Factors affecting the rate of enzymatic reactions
Inhibitors
• inhibitors (抑制劑) are chemicals that
slow down or stop the activities of
enzymes
84
4.3 Factors affecting the rate of enzymatic reactions
Inhibitors
Competitive
inhibitors
(競爭性抑制劑)
Non-competitive
inhibitors
(非競爭性抑制劑)
85
4.3 Factors affecting the rate of enzymatic reactions
1 Competitive inhibitors
Animation
competitive
inhibitor
substrate
similar shape!
86
4.3 Factors affecting the rate of enzymatic reactions
1 Competitive inhibitors
• compete with substrates for active sites
substrate
inhibitor
active site
enzyme
87
4.3 Factors affecting the rate of enzymatic reactions
1 Competitive inhibitors
reaction rate
decreases
enzyme
inhibitor prevents
binding of substrate
chance to form
enzyme-substrate
complex lowered
88
4.3 Factors affecting the rate of enzymatic reactions
1 Competitive inhibitors
enzyme
reversible binding
substrate can bind
when inhibitor
leaves
89
4.3 Factors affecting the rate of enzymatic reactions
1 Competitive inhibitors
more substrates,
greater chance
of binding
reaction rate
increases
90
4.3 Factors affecting the rate of enzymatic reactions
Inhibitors
Competitive
inhibitors
(競爭性抑制劑)
Non-competitive
inhibitors
(非競爭性抑制劑)
91
4.3 Factors affecting the rate of enzymatic reactions
2 Non-competitive inhibitors
substrate
noncompetitive
inhibitor
shape not similar
• do not compete for active sites
92
4.3 Factors affecting the rate of enzymatic reactions
2 Non-competitive inhibitors
active site
changes
shape
93
4.3 Factors affecting the rate of enzymatic reactions
2 Non-competitive inhibitors
not fit together!
reaction rate
decreases
94
4.3 Factors affecting the rate of enzymatic reactions
2 Non-competitive inhibitors
• increasing substrate concentration
cannot increase reaction rate
95
4.3 Factors affecting the rate of enzymatic reactions
2 Non-competitive inhibitors
• examples:
cyanide
heavy
metals
96
4.3 Factors affecting the rate of enzymatic reactions
4.4
Video
Investigation of the effect of inhibitors
on enzyme activity
1 Add Benedict’s solution to test tubes 1 to 3.
2 Prepare test tubes A to C.
A
B
C
copper(II)
silver
distilled
suphate
nitrate +
water +
+sucrose
sucrose
sucrose
97
4.3 Factors affecting the rate of enzymatic reactions
4.4
3 Add 10 drops of invertase solution to test
tubes A to C. Leave the tubes at room
temperature for 5 minutes.
98
4.3 Factors affecting the rate of enzymatic reactions
4.4
4 Pour Benedict’s solution in test tubes 1
to 3 into test tubes A to C respectively.
Shake the tubes gently. Put the test tubes
into a boiling water bath for 10 minutes.
boiling water
99
4.3 Factors affecting the rate of enzymatic reactions
4.4
5 Allow the tubes stand for 15 minutes.
Measure the depth of any brick-red
precipitate settled in the test tubes.
100
4.3 Factors affecting the rate of enzymatic reactions
4.4
Results and discussion
• Precipitate is formed in control set-up
(tube C). No precipitate is formed in
tubes A and B.
• The results show that copper(II) ion and
silver ion are inhibitors of enzyme
invertase. Their presence slows down the
action of invertase on sucrose.
101
4.3 Factors affecting the rate of enzymatic reactions
1 Effect of temperature on enzymes:
Temperature
Enzymes
Low temperature Inactive
Optimum
Work best
temperature
High temperature Denatured
102
4.3 Factors affecting the rate of enzymatic reactions
2 Effect of pH on enzymes:
pH
Enzymes
Optimum pH
Work best
Extreme pH
Denatured
103
4.3 Factors affecting the rate of enzymatic reactions
3 Difference between competitive and
non-competitive inhibitors:
NonCompetitive
competitive
Shape of
molecule
Are they similar to
Similar
Not similar
substrate?
104
4.3 Factors affecting the rate of enzymatic reactions
3 Difference between competitive and
non-competitive inhibitors:
Action
NonCompetitive
competitive
Compete Change the
What is their
shape of
for active
mode of action?
enzyme
site
105
4.3 Factors affecting the rate of enzymatic reactions
3 Difference between competitive and
non-competitive inhibitors:
NonCompetitive
competitive
Will the rate of
Increased
substrate
No
Yes
enzymatic
reaction
concentration
increase?
106
4.4 Applications of enzymes
• used to produce useful commercial
products
107
4.4 Applications of enzymes
• example:
lipases and proteases
to remove stains
containing lipids and
proteins
biological washing
powder
108
4.4 Applications of enzymes
• example:
a protease extracted
from papaya
papain
to soften meat
meat tenderizer
109
4.4 Applications of enzymes
• example:
cheese
extracted from young
cows’ stomach
proteases
to coagulate (凝固)
milk in cheese
production
110
4.4 Applications of enzymes
• example:
enzymes
to modify starch to
keep the bread soft
bread
111
4.4 Applications of enzymes
• example:
enzymes
to break down plant
cell walls so that the
juice looks less
cloudy
fruit juice
112
4.4 Applications of enzymes
• example:
enzymes
to remove hairs from
hides (牛皮)
to soften leather
leather
113
4.4 Applications of enzymes
What are the advantages of
using enzymes?
114
4.4 Applications of enzymes
1
Specific in action
• reduce the production of unwanted
products
115
4.4 Applications of enzymes
2
Efficient in small amount
• lower the cost of production
116
4.4 Applications of enzymes
3
Work at moderate conditions
• extreme and expensive conditions not
required
e.g. high temperature
high pressure
117
4.4 Applications of enzymes
4.5
Investigation of protease activities in
different fruit juices
1 Heat the end of a cork borer in a Bunsen
flame and allow it to cool.
118
4.4 Applications of enzymes
4.5
2 Gently press the borer down into the
milk-agar plate to make five wells.
Replace the lid quickly.
milk agar plate
cork
borer
well
119
4.4 Applications of enzymes
4.5
3 Use a clean dropper to fill the wells A–D
with pineapple juice, kiwi fruit juice,
papaya juice and guava juice. Fill well E
with distilled water.
different fruit juices
distilled water
120
4.4 Applications of enzymes
4.5
4 Replace the lid. Incubate the plate at
35˚C for one hour.
incubator
121
4.4 Applications of enzymes
4.5
5 Measure the diameter of the clear zones
around the wells by placing the plate on
graph paper and examining against light.
122
4.4 Applications of enzymes
4.5
Results and discussion
• Clear zones are observed around the wells
containing fruit juices and their diameters
are different.
• The well containing distilled water is a
control. No clear zone is formed around it.
123
4.4 Applications of enzymes
4.5
Results and discussion
• The results show that pineapple, kiwi
fruit, papaya and guava contain
proteases that can break down proteins,
but the activities of the proteases
differ from one another.
124
4.4 Applications of enzymes
4.6
Video
Design an investigation of the
effectiveness of different biological
washing powder
Which brand of biological
washing powder is the most
effective in removing food
stains? Design an investigation
to find this out.
125
4.4 Applications of enzymes
Enzyme are widely used in industry
to produce useful products e.g.
biological washing powder and
meat tenderizers . They are also
important in food industries,
breweries and leather industries.
126
1
What are enzymes?
Enzymes are biological
catalysts. They speed up
metabolic reactions in
organisms.
enzyme
127
2
What is the importance
of enzymes to organisms?
Without enzymes, metabolic
reactions will not proceed
enzyme
under the relatively low
temperatures.
128
3
What is the advantage of
using enzymes in the making
of stonewashed jeans?
This can shorten the time
of jean production.
enzyme
129
Enzymes
lower the
energy barrier
therefore speed up
metabolic reactions
include
anabolic catabolic
reactions reactions
130
Enzymes
have an
active site
shows
specificity
can be explained by
lock-and-key hypothesis
131
Enzymes
activities affected by
temperature pH inhibitors
too low too high
causes causes
extreme values
cause
inactivation denaturation
of enzymes of enzymes
132
inhibitors
may be
competitive
non-competitive
133