4
4.1

Enzymes and metabolism
Metabolism (Book 1A, p. 4-3)
Metabolism (新陳代謝) refers to the (1) _______________ of the chemical reactions that take
place in an organism to keep it alive.
Catabolism (分解代謝)

All the (2) _______________ reactions
Anabolism (合成代謝)

within an organism

(3) _______________ energy
All the (4) _______________ reactions
within an organism

(5) _______________ energy
4.2
Properties and actions of enzymes (Book 1A, p. 4-4)
A
What is the role of enzymes in metabolism? (Book 1A, p. 4-4)

To start a chemical reaction, enough energy must be supplied to the reacting molecules so
that they can overcome the (1) _______________ _______________ (能障).

Enzymes (酶) are (2) _______________ which act as biological (3) _____________
(生物催化劑).

Enzymes can speed up the rate of chemical reactions by (4) _______________ the energy
barrier so that reactions can take place at body temperature.

Metabolic reactions would proceed very (5) _______________ or even stop without
enzymes.
B

How do enzymes work? (Book 1A, p. 4-6)
Each enzyme molecule has an (6) _______________ _______________, which is
(7) _______________ (專一的) in shape.

The active site of an enzyme molecule combines with the substrate molecules that fits the
active site to form an (8) ______________________ _______________. The
formation of the complex lowers the energy barrier of the reaction.

In catabolic reactions, the enzyme helps to (9) _______________ the substrates apart.
Ch.4 Enzyme / P.1

In anabolic reactions, the enzyme helps to (10) _______________ the substrates together.

The complex then breaks down to give the (11) _______________. The enzyme is released
in its (12) _______________ form.
Specificity of enzyme:

The (13) _______________ hypothesis (鎖鑰假說) explains
the specificity of enzyme action.

Enzymes combine with particular (14) _______________
only, like a key only fits in a particular
(15) _______________.
What are the properties of enzymes? (Book 1A, p. 4-7)
C
1
Enzymes are biological catalysts.

2
They can (16) _______________ _______________ metabolic reactions.
Enzymes can be (17) _______________.

They combine temporarily with the substrates during reactions, but return to the
original form and released after reaction.
3
Enzymes are required in relatively (18) _______________ amount.
4
Enzymes are (19) _______________.

5
Their structures and functions are easily affected by (20) _______________ and pH.
The actions of enzymes are (21) _______________.

Each enzyme catalyses only one type of reaction.
Ch. 4 Enzyme / P.2
4.3
Factors affecting the rate of enzymatic reactions
(Book 1A, p. 4-9)

Enzyme activity is usually expressed in terms of (1) _______________ _______________ of
an enzymatic reaction, which is the rate at which the substrates are used up or broken down,
or the rate of the formation of product(s).
A
Temperature (Book 1A, p. 4-9)
 Effect of temperature on the rate of enzymatic reaction
Temperature
Effect on the rate of enzymatic reactions

Low
temperatures
At around 0°C, enzymes become (2) inactive/active and the reaction rate
is (3) low/high.

As temperature rises, the molecules have (4) less/more kinetic energy
and collide (5) less/more frequently. This leads to a (6) lower/higher
chance to form an enzyme-substrate complex.
Optimum

(7) minimum/maximum.
temperature
High
Enzymes work best and the reaction rate reaches a

temperatures
Enzyme molecules change shape and denatured (變性), so the rate of
reaction (8) decreases/increases.
Misconception
Some students wrongly think that enzymes are killed by heating so the rate of enzymatic
reaction decreases. Enzymes are NOT living things. They cannot be killed. They are denatured
(their shapes are changed) at very high temperatures.
Ch.4 Enzyme /P.3
B
pH (Book 1A, p. 4-11)
 Effect of pH on the rate of enzymatic reaction

Each enzyme works in a (9) _______________ range of pH. An enzyme works best at its
(10) _______________ pH.

C

Enzymes become (11) _____________ at unsuitable pH. Therefore enzyme activity decreases.
Inhibitors (Book 1A, p. 4-12)
Enzyme activity can be slowed down or even stopped by (12) _______________ (抑制劑).
(13) ______________________
(14) ______________________
______________________
______________________
(競爭性抑制劑)
(非競爭性抑制劑)
Similar to substrate molecules
Not similar to substrate molecules
Shape of
molecule
Action
inhibitor
substrate
inhibitor
(15) _______________ with the
Attaches to other parts of the
substrate molecules for active site
enzyme to change its
by binding to the active site of the
(16) ______________, so that the
enzyme
substrate molecules can no longer fit
into the active site
Ch. 4 Enzyme / P.4
substrate
substrate
substrate
enzyme
inhibitor
enzyme
inhibitor
Effect of
The rate of enzymatic reaction
The rate of enzymatic reaction does
increasing
(17) _______________
not increase
substrate
concentration
4.4
Applications of enzymes (Book 1A, p. 4-16)
Enzymes are widely used in industrial processes to produce useful products. For example:
Washing powder
Meat tenderizer (鬆肉粉)
Cheese
Proteases and lipases are
Papain extracted from papaya is
added to remove stains.
added to (1) ____________ meat. (2) _______________ milk.
Bread
Juice
Proteases are used in
Leather
Enzymes modify the
Enzymes are used to break down
Enzymes are used to remove
(3) ____________ in bread,
plant cell walls in fruit juices, so
hairs from hides (牛皮) and
so that the bread can keep
that the juices look less cloudy.
(4) ___________ the leather.
softer for a longer time.
Ch.4 Enzyme /P.5
Advantages of using enzymes in industrial processes:

Production of unwanted products can be reduced due to the (5) _______________ of
enzyme action.

Cost of production can be (6) _______________ as enzymes are efficient in small amounts.

Extreme and expensive conditions are not required because enzymes can work at
(7) _______________ conditions.
Exercise
A student carried out an investigation to study the effect of temperature on amylase activity. He
prepared 5 test tubes, each contained 5 cm3 of starch solution and 1 cm3 of amylase solution. He put
the tubes in water bath of different temperatures (0°C, 20°C, 40°C, 60°C and 80°C). He measured
the time for all the starch in the test tubes to disappear. The results are shown in the graph below.
time needed for
the disappearance
of all starch
0
a
20
40
60
80
temperature / °C
Suggest a method to test for the presence of starch in the test tube.
(1 mark)
____________________________________________________________________________
b
Describe and explain the results at the following temperatures:
i
below 60°C
(3 marks)
________________________________________________________________________
________________________________________________________________________
ii
above 60°C
(2 marks)
________________________________________________________________________
________________________________________________________________________
c
State two variables that should be kept constant in the above investigation.
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
d
If acid is added to the test tubes, the starch will not disappear. Why?
(2 marks)
____________________________________________________________________________
____________________________________________________________________________
Total: 10 marks
Ch. 4 Enzyme / P.6
Answers
Ch 4
Enzymes and metabolism
4.1
1
sum
2
breaking-down
3
Releases
4
1
energy barrier
2
proteins
3
catalysts
4
6
active site
7
specific
8
enzyme-substrate complex
10
join
11
products
12
original
13
15
lock
16
speed up
17
reused
20
temperature
21
specific
1
reaction rate
2
inactive/active
3
low/high
6
lower/higher
7
minimum/maximum
10
optimum
11
denatured
14
Non-competitive inhibitor
building-up
5
Requires
5
slowly
9
split
lock-and-key
14
substrates
18
small
19
proteins
4
less/more
5
less/more
8
decreases/increases 9
4.2
lowering
4.3
12
inhibitors
13
Competitive inhibitor
15
Competes
16
shape
17
3
starch
4
soften
5
narrow
increases
4.4
1
soften
2
coagulating
6
lowered
7
moderate
specificity
Exercise
a
Iodine test
1m
b
i
At below 60°C, the amylase activity increases and reaches a maximum at about 60°C.
1m
At low temperature, the enzymes are inactive and the reaction rate is slow.
1m
As the temperature rises, the kinetic energy of the enzyme molecules increases, so they vibrate more frequently. This
ii
increases the chance to form an enzyme-substrate complex.
1m
At above 60°C, the amylase activity decreases with the increase in temperature.
1m
Enzymes become denatured at high temperatures.The active sites of the enzymes can no longer fit the substrate
molecules.
c
Any two from:
1m
1m × 2
Concentration of amylase solution
Concentration of starch solution
pH of the reaction mixtures
d
Amylase is denatured at very low pH.
1m
Reaction rate becomes very slow, so starch remains in the solution.
1m
Ch.4 Enzyme /P.7