think about… 4.1 metabolism 4.2 properties and actions of enzymes

2

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

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Want old, worn-out jeans?

I can help you!

4

Wash jeans with stones.

Stones break some cellulose fibres & remove the blue dye.

5

enzyme

Now we can use enzymes to break down the fibres more

quickly!

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1What are enzymes

enzyme

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2

enzyme

What are theimportance of enzymes to organisms

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What are the advantages of using enzymes in the making of stonewashed jeans

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enzyme

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• different chemical reactions take place in living cells

4.1 Metabolism

respiration

protein synthesis

lipid synthesis

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• different chemical reactions take place in living cells

4.1 Metabolism

sum of the chemical reactions that take place in an organism

= metabolism (新陳代謝 )

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Metabolism

Anabolism

(合成代謝 )

Catabolism

(分解代謝 )

4.1 Metabolism

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complex molecule

simple molecules

1 Catabolism

energy

4.1 Metabolism

• breaking-down reactions• release of energy

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• example: respiration

4.1 Metabolism

glucose

water

1 Catabolism

energy

carbon dioxide

+

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Metabolism

Anabolism

(合成代謝 )

Catabolism

(分解代謝 )

4.1 Metabolism

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simple molecules

complex molecule

energy

4.1 Metabolism

• building-up reactions• requires energy

2 Anabolism

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• example: condensation of glucose

4.1 Metabolism

glucose

2 Anabolism

energy

starch

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Anabolism

Metabolism

Catabolism

What are catabolism, anabolism and metabolism?

all breaking-down reactions in an organism

all building-up reactions in an organism

all chemical reactions in an organism

4.1 Metabolism

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What is the role of enzymes in

metabolism?

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reacting molecules

product (生成物 )

energy barrier (能障 )

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energy

reacting molecules

product (生成物 )

energy barrier (能障 )

Energy supplied to overcome the energy barrier

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reacting molecule

product

•analogy: pushing a rock up a hill 4.2 Properties and actions of enzymes

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the reaction does not start due to the presence of energy barrier


reacting molecule

productenergy barrier

•analogy: pushing a rock up a hill

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energy

when energy is supplied …

maximum energy

reaction starts


•analogy: pushing a rock up a hill

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How can the energy barrier be overcome in our body?


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By increasing the temperature?

• energy level raised


energy barrier is easier to overcome

smaller energy barrier

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By increasing the temperature?


smaller energy barrier

• energy level raised energy barrier is easier to overcome

Not possible because high temperature

kill the body cells!

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lower energy barrier


• rate of chemical reactions is speeded up by enzymes (酶 )

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energy


• rate of chemical reactions is speeded up by enzymes (酶 )

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4.1

Demonstration of the breaking-down action of enzymes


1 Prepare liver extract.

fresh pig liver

a Grind fresh liver with cold distilled water.

cold distilled water

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filter paper

liver extract

b Filter the ground tissue with filter paper.


4.1

31

distilled water

liver extract

c Dilute the liver extract by 50% with cold distilled water.


4.1

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2 Set up 3 test tubes A to C. Observe for the release of gas and the gas given off with a glowing splint.

hydrogen peroxide

+ liver extractA

distilled water + liver extract

hydrogen peroxide + distilled waterB C


4.1

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Results and discussion

• A gas is released from tube A.

The gas is oxygen becauseit re-lights a glowing splint.• No oxygen is released from the control set-ups (tubes B and C).


4.1

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• 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.



4.1

35

enzyme

active site (活性部位 )

• each enzyme has an active site of a specific (專一的 ) shape


How do enzymes work?

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enzyme

substrate shapes fit together!

• active site can combine with substrate (受質 ) molecule(s)



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• complex breaks down to give product(s)

• active site can combine with substrate (受質 ) molecule(s)

enzyme-substrate complex (酶受質複合物 )



enzyme

substrate

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enzyme- substrate complex

• in catabolic reactions:



substrate

enzyme

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enzyme unchanged and can be reused


• in catabolic reactions:

products



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• in anabolic reactions:




substrates

enzyme

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• in anabolic reactions:


product



enzyme unchanged and can be reused

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• act as catalysts (催化劑 ) in organisms

Properties of enzymes

1) Biological catalysts

speed up metabolic reactions


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• enzyme returns to its original form after reaction


2) Reusable

after reaction

same!

before reaction


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3) Required in small amount

large amount of products produced


reusablereusablereusable

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4) Proteins

• enzymes are denatured (變性 ) at high temperatures and extreme pH


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5) Specific action


different shape!

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5) Specific action• each enzyme combines with a specific

substrateeach enzyme catalyses only one

type of reaction


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• can be explained by


lock-and-keyhypothesis(鎖鑰假說 )


5) Specific action

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Lock-and-key hypothesis

• fit only a particular lock


specific shape

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• fit only a particular substrate


active sites of specific shape

Lock-and-key hypothesis

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Enzymes are biological catalysts

that chemical reactions

in organisms by lowering the

of reactions.

They are important in regulating

metabolism.

energy barrier

speed up

1


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An enzyme works when its

combines with substrate

(s) to form an

. The c

omplex then breaks down to give the

product(s). The enzyme is released in

its .

active site

original form

enzyme-substrate complex

2


53

Enzyme actions are specific becaus

e their active sites have

. Enzyme combin

es only with substrate(s) that fits into

its active site. The specificity of enzy

me actions can be explained by the

.

specific shapes

3

lock-and-key hypothesis


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Five properties of enzymes:

i) They are biological

.

ii) They can be .

iii) They are required in

amount.

iv) They are .

v) Their actions are .

catalysts

specific

proteins

reused

small

4


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Enzyme activity• reaction rate of an enzymatic reaction= the rate at which substrates are

used up or broken down= the rate of product formation


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enzyme


Enzyme activity• reaction rate of an enzymatic reaction= the rate at which substrates are

used up or broken down= the rate of product formation

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enzyme


temperature pH

inhibitor

temperature

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Temperature

temperature( )℃

reaction rate

0 10 20 30 40 50 60

0˚C low kinetic energy

enzyme inactive


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temperature( )℃

reaction rate

0 10 20 30 40 50 60

temperature rises

more kinetic energy


Temperature

60

have higher chance to form an enzyme-substrate complex

molecules vibrate more rapidly

collide more frequently


more kinetic energy

Temperature

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Temperature

temperature( )℃

reaction rate

0 10 20 30 40 50 60

temperature rises

more kinetic energy

reaction rate increases

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Temperature

temperature( )℃

reaction rate

0 10 20 30 40 50 60

optimum temperature rate of enzymatic reaction reaches maximum

maximum rate


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Temperature

temperature( )℃

reaction rate

0 10 20 30 40 50 60

temperature higher than optimum temperature enzyme denatured

reaction rate decreases


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Enzymes are killed by heating so the rate of enzymatic reaction decreases.


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Enzymes are NOT living things. They cannot be killed. They are denatured (their shapes are changed) at very high temperatures.


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4.2

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.

Simulation

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4.2

ice

A 1

0˚C

B 2

20˚C

C 3

40˚C

D 4

60˚C

E 5

80˚C

F 6

100˚C

starch solution

amylase solution


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4.2

3 Pour the amylase solution into starch solution. Put the tube of mixture back to its beaker. Record the time as zero.

A

1

amylase solution

starch solution


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4.24 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


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4.2


• 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.

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4.2

• At low temperature, the enzymatic reactionrate is low because amylase is inactive.

• Its activity increases with temperature until it reaches a maximum (around 60˚C).



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4.2

• 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.



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enzyme


temperature pH

inhibitor

pH

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reaction rate

2 4 6 8 10 12 14pepsin

many enzymes in mammals (e.g.

salivary amylase)

pancreatic lipase

pH4.3 Factors affecting the rate of enzymatic reactions

pH

752 4 6 8 10 12 14

reaction rate

each enzyme works in a narrow range of pH

pH


762 4 6 8 10 12 14

reaction rate

each enzyme have their own optimum pH

unsuitable pH causes denaturation

optimum pH for most enzymes: pH 5 – pH 9


pH

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4.3

Investigation of the effect of pH on enzyme activity


1 Add Benedict’s solution to test tubes 1 to 6.

Benedict’s solution

Simulation

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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 A B C D E F

pH of buffer solution

3.2 4.0 5.2 6.0 7.0 8.0

4.3


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3 Add invertase solution to test tubes A to F. Leave at room temperature for 5 minutes.

4.3

sucrose solution + citrate-phosphate buffer + invertase


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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.

4.3

boiling water


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5 Allow the tubes to stand for 15 minutes.Measure the depth of any brick-red precipitate settled in the test tubes.

4.3


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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.


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enzyme


temperature pH

inhibitor inhibitor

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Inhibitors4.3 Factors affecting the rate of enzymatic reactions

• inhibitors (抑制劑 ) are chemicals that slow down or stop the activities of enzymes

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Competitiveinhibitors

(競爭性抑制劑 )

Non-competitiveinhibitors

(非競爭性抑制劑 )

Inhibitors


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1 Competitive inhibitors

substratecompetitive inhibitor

similar shape!


Animation

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• compete with substrates for active sites

active site

enzyme


substrateinhibitor


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inhibitor prevents binding of substratechance to form enzyme-substrate complex lowered


enzyme



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substrate can bind when inhibitor leaves

reversible binding


enzyme


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reaction rate increases

more substrates, greater chance of binding



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Inhibitors

Competitiveinhibitors

(競爭性抑制劑 )

Non-competitiveinhibitors

(非競爭性抑制劑 )


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substratenon-competitive inhibitor

shape not similar

2 Non-competitive inhibitors4.3 Factors affecting the rate of enzymatic reactions

• do not compete for active sites

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2 Non-competitive inhibitors

active site changes shape


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not fit together!


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• increasing substrate concentration cannot increase reaction rate


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• examples:


cyanideheavy metals

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4.4

Investigation of the effect of inhibitors on enzyme activity


Acopper(II) suphate +sucrose

1 Add Benedict’s solution to test tubes 1 to 3.

2 Prepare test tubes A to C.Bsilver nitrate + sucrose

Cdistilled water + sucrose

Video

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4.4

3 Add 10 drops of invertase solution to test tubes A to C. Leave the tubes at room temperature for 5 minutes.


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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


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4.4

5 Allow the tubes stand for 15 minutes.Measure the depth of any brick-red precipitate settled in the test tubes.


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4.4


• 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.


102

1 Effect of temperature on enzymes:

Temperature Enzymes

Low temperature

Work best

High temperature

Inactive

Optimum temperature

Denatured


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2 Effect of pH on enzymes:

pH Enzymes

Work best

Extreme pH

Optimum pH

Denatured


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3 Difference between competitive and non-competitive inhibitors:

Competitive Non-

competitive

Shape of molecule


Are they similar to substrate?

Similar Not similar

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Competitive Non-

competitive

Action


What is their mode of action?

Change the shape of enzyme

Compete for active

site


106

Competitive Non-

competitive

Increased substrate concentration


Will the rate of enzymatic reaction

increase?Yes No


107


• used to produce useful commercial products

108

• example:

lipases and proteasesto remove stains

containing lipids and proteins

biological washing powder


109

• example:

papainto soften meat

meat tenderizer

a protease extracted from papaya


110

• example:

proteasesto coagulate (凝固 )

milk in cheese production

cheese

extracted from young cows’ stomach


111

• example:

to modify starch to keep the bread soft

bread


enzymes

112

• example:

to break down plant cell walls so that the juice looks less cloudy

fruit juice


enzymes

113

• example:

to remove hairs from hides (牛皮 )

to soften leatherleather


enzymes

114

What are the advantages of using enzymes?


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• reduce the production of unwanted products

Specific in action1


116

• lower the cost of production

Efficient in small amount2


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• extreme and expensive conditions not required

Work at moderate conditions3


e.g. high temperaturehigh pressure

118

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.

119

4.5


cork borer

wellmilk agar plate

2 Gently press the borer down into the milk-agar plate to make five wells. Replace the lid quickly.

120

4.53 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.

distilled water

different fruit juices


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4.5

4 Replace the lid. Incubate the plate at 35˚C for one hour.

incubator


122

4.5

5 Measure the diameter of the clear zones around the wells by placing the plate on graph paper and examining against light.


123

4.5


• 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.


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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.


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4.6

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.


Video

126

tenderizers

Enzyme are widely used in industry

to produce useful products e.g.

biological and

meat . They are also

important in food industries,

breweries and leather industries.

washing powder


127

enzyme

What are enzymes?1Enzymes are biological catalysts. They speed up metabolic reactions in organisms.

128

enzyme

What is the importance2Without enzymes, metabolic reactions will not proceed under the relatively low temperatures.

of enzymes to organisms?

129

enzyme

What is the advantage of 3

This can shorten the time of jean production.

using enzymes in the making of stonewashed jeans?

130

lower the

Enzymes

metabolic reactions

energy barriertherefore speed up

include

anabolic reactions

catabolic reactions

131

Enzymes have an

active site

specificity

lock-and-key hypothesis

shows

can be explained by

132

Enzymes activities affected by

temperature pH inhibitors

inactivation of enzymes

denaturation of enzymes

too low causes

too high causes

extreme values cause

133

inhibitors

competitive non-competitive

may be

think about… 4.1 metabolism 4.2 properties and actions of enzymes

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