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Enzymes

Cells need energy from food, In your groups, write down how you think enzymes help this process

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Enzyme

catalyst

speeds up reactions in cells

works best at certain pH and temp

found inside cellsis protein

each one is specific to a certainreactant

has an active site

can be used again and again

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Objectives: Be able to describe enzymes as proteins that act as biological catalysts. Know how temperature and pH affect enzyme activity (optimum conditions)

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How do chemical reactions happen?

Reactants Products

A B

For reactants 'A' and 'B' to combine, they must hit each other (collide) at a specific point

A B+

This is random and very difficult. If we heat the reactants, they have more kinetic energy and will move faster. As they move faster they will increase their chances of colliding in the right places

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How do chemical reactions happen?

Reactants Products

enzyme

A B

An enzyme has a specific area, called the active site .

The active site has a shape that allows the reactants to fit in at the right position so they join together. The enzyme can be reused.

A B

enzyme

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Time

Energy in the system

reactants

C

HO

H

H H

O

O O

O O

C

H

HH

HO

OO

O

O

O

C O H

O

OH

O

OH

O

O

+

energy putin to startreaction

energy givenout as HEAT

activation energy

product

How enzymes lower activation energy

C

H

O

H

H H O

energy is containedin chemical bonds

Let's consider energy in methane and oxygen.

To make these react we have to break these bonds. That takes energy

C

H

O

HH

H

O

O O

O

OO

O

O

O

Now they are separate atoms that can combine in their lowest energy state.

C O H

O

OH

O

OH

O

O

+

In this case carbon monoxide and water is formed. Excess energy is released as heat.

+ HEAT ENERGY

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Enzymes speed up reactions by lowering the activation energy needed to start the reaction

energy

time

activation energy

product

no enzyme

enzyme

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Facts about enzymes:

They are proteins They work best at certain pH and temperatures They are specific, only acting on one type of substance They speed up reactions and can be used again Their name usually ends in -ase

eg. protease, amylase, lipase

Use the following animations to help you understand how enzymes work:

http://highered.mcgrawhill.com/sites/0072495855/student_view0/chapter2/animation__how_enzymes_work.html

http://www.northland.cc.mn.us/biology/Biology1111/animations/enzyme.swf

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What factors affect the speed of enzyme-catalysed reactions?

Objectives:

Know that enzymes have optimum conditionsInvestigate optimum temperature for an enzyme

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Remember that enzymes are proteins. They have optimum conditions where they work best

Amylase is an enzyme found in the mouth. It catalyses the breakdown of starch into glucose.

The time taken for amylase to convert starch into glucose was tested and the results are shown below. If the reaction took more than 8.0 minutes, it was deemed to be unreactive.

Read the following data and plot the graph:

Time takenfor reaction (min)

pH 1 2 3 4 5 6 7

8 9 10 11 12 13 14Time takenfor reaction (min)

pH

0.52.05.08.0xxx

2.0 4.0 7.0 8.0 x x x

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1 2 3 4 5 6 7 8 9 10 11 12 13 14pH

1.0

0

2.0

3.0

4.0

5.0

6.0

7.0

8.0

x

x

x

x

x

x

x

x

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Measuring rates of reaction

Aim:

Measure how temperature affects the rate of an enzyme catalysed reaction

Enzyme reactions are usually measured as rate of reaction. We can do this in the class by using the following experiment:

Cells contain an enzyme called catalase. This enzyme will break down hydrogen peroxide into water and oxygen. The reaction is as follows:

2H2O2 (aq) 2H2O (l) + O2 (g)

Theory:

We can measure the rate of reaction by measuring the amount of oxygen produced.

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Method:

Working in groups, each group will investigate the effects of temperature on 1 set of results

The results will be pooled and the best average (mean) calculated

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Method:

Add 5 ml of CELERY extract to a test tube Add 20 ml of hydrogen peroxide to a second boiling tube Place the tubes in the water bath for 1 - 2 minutes Add the celery to the hydrogen peroxide Time how much gas is produced every 30 seconds for 5 minutes Record your results in the spread sheet If no gas is produced in 5 minutes, treat it as a null result

Temperatures to use:

20, 30 , 40 , 50 and 60

CAREWITHHOTHYDROGENPEROXIDESAFETYGLASSESMUSTBEWORN

Measuringanenzyme.docxEnzymecatalysedreaction.xlsx

Measuring an enzyme-catalysed reaction

You are going to measure the rate of a reaction that happens because of an enzyme in celery.

Most cell contain an enzyme called catalase. This enzyme convert hydrogen peroxide into water and oxygen.

The reaction is as follows:

2H2O2 (aq) catalase 2H2O (l) + O2 (g)

If the rate of oxygen production is measured then the rate of the reaction can be calculated.

The effect of temperature on the reaction can be investigated.

Method:

Label 5 test tubes and 5 boiling tubes A - E

Add 5 cm3 of celery extract to each test tube

Add 20 cm3 of hydrogen peroxide to each boiling tube

Set the water bath to 60oC

Place tubes A into the 60oC water bath and wait for 1 2 minutes

Prepare the gas collecting water bath

Quickly add the celery extract to the hydrogen peroxide and measure the amount of gas produced every 30 seconds for 5 minutes

Repeat the experiment for 50, 40, 30 and 20oC

Record your results in the excel sheet prepared

BE CAREFUL WITH HOT HYDROGEN PEROXIDE

SAFETY GLASSES NEED TO BE WORN AT ALL TIMES

SMART Notebook

Sheet1

Time (seconds)

temp = 600306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 500306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 400306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 300306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 200306090120150180210240270300

1

2

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7

8

av

Sheet2

Sheet3

SMART Notebook

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XXXXXXX

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Results:

Draw a graph from the table of results

What type of graph will you draw?What label is the 'x' axis?

30 60 90 120 150 1806050403020

Time (seconds)

T

e

m

p

e

r

a

t

u

r

e

(

)

Use the graph to work out the values

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60 120 1800 240Time (seconds)

0

10

20

30

40

50

60

70

g

a

s

p

r

o

d

u

c

e

d

(

m

l

)

60

50

40

30

20

xx

xx x x

x

x

x

x

xx

x

x

x

x

x

x

xx

x

x

x

x

x

xx

temperature ( )Rate of enzyme reaction

x

x

x

x

x

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Conclusion:

What do your results show you about how the rate of the reaction changes with temperature? What does this mean is happening with the enzyme at different temperatures?

Review the links on enzyme action.

At low temperatures, the enzyme is slowed down but still works.

At too high a temperature, the enzyme is denatured and will not work

At the optimum temperature, the enzyme works the fastset

pH also affects enzymes

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Salivary amylase is an enzyme that works in the mouth of humans. The pH of the mouth is 7. The normal temperature is about 37 .

What would happen if amlase was placed in a solution of pH 2? What would happen if amylase was place in a solution of pH 7 at

20 , or at 60 ?

pH 2 would denature the amylase. The active site would be damaged so it does not have the same shape as the reactants anymore. The enzyme wil not work.

At 20 , the enzyme would work slowly. At 60 , the enzyme's active site would be denatured and so the enzyme wil not work.

Answers:

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Attachments

Measuringanenzyme.docx

Enzymecatalysedreaction.xlsx

Measuring an enzyme-catalysed reaction

You are going to measure the rate of a reaction that happens because of an enzyme in celery.

Most cell contain an enzyme called catalase. This enzyme convert hydrogen peroxide into water and oxygen.

The reaction is as follows:

2H2O2 (aq) catalase 2H2O (l) + O2 (g)

If the rate of oxygen production is measured then the rate of the reaction can be calculated.

The effect of temperature on the reaction can be investigated.

Method:

Label 5 test tubes and 5 boiling tubes A - E

Add 5 cm3 of celery extract to each test tube

Add 20 cm3 of hydrogen peroxide to each boiling tube

Set the water bath to 60oC

Place tubes A into the 60oC water bath and wait for 1 2 minutes

Prepare the gas collecting water bath

Quickly add the celery extract to the hydrogen peroxide and measure the amount of gas produced every 30 seconds for 5 minutes

Repeat the experiment for 50, 40, 30 and 20oC

Record your results in the excel sheet prepared

BE CAREFUL WITH HOT HYDROGEN PEROXIDE

SAFETY GLASSES NEED TO BE WORN AT ALL TIMES

SMART Notebook

Sheet1

Time (seconds)

temp = 600306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 500306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 400306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 300306090120150180210240270300

1

2

3

4

5

6

7

8

av

Time (seconds)

temp = 200306090120150180210240270300

1

2

3

4

5

6

7

8

av

Sheet2

Sheet3

SMART Notebook

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