Unit 3 Enzymes What you need to be able to do:

B3. Enzymes1 Define enzymes as proteins that function as biological catalysts.2 Investigate and describe the effect of changes in temperature and pH on enzyme activity.3 Explain the effect of changes in temperature and pH on enzyme activity

What do you already know?

Enzymes

Carry out this experiment:

ResultsComplete the table:

Contents of Tube Observations Explanation

Complete the definitions:

A catalyst...

Enzymes...

Watch the Enzymes video http://www.youtube.com/watch?v=0XjyAkeQJag and make your own notes

Now complete the paragraph below by adding the missing words:

Enzymes are_________ ____________.

They speed up chemical reactions in _________ things. Each enzyme catalyses one reaction,

we say they are ____________.

e.g. protease breaks down ___________ and ________ breaks down lipids (fats and oils).

Their names end in "______".

The enzymes are not _________ ______ but can be used many times to catalyse the same

reaction.

The substance that the enzyme breaks down is called the __________. The substance that is

made is called the ________. They work by the ________ ____ _____mechanism.

Enzymes are affected by _____ and _____________. Enzymes have an _______________ pH

and temperature at which they work best. At low temperatures enzyme work ________ but at

high temperatures they may become ______________.

Factors Affecting Enzyme Activity

Open up the link: http://www.kscience.co.uk/animations/anim_2.htmThe last animation is a virtual experiment that lets you manipulate different variables and see their effect on the enzyme.

Effect of changing enzyme concentrationChoose 1 enzyme and 20 substrates. Leave all other settings the same.Let the animation run for 30 seconds and then record the number of product molecules formed.Repeat the experiment but change the number of enzymes.

Number of enzyme molecules Number of product molecules formed in 30s

1

What is the effect of increasing the concentration of enzymes?

Can you explain why this happens? Effect of changing substrate concentrationChoose 1 enzyme and 20 substrate molecules. Leave all other settings the same.Let the animation run for 30 seconds and then record the number of product molecules formed.Repeat the experiment but change the number of substrate molecules.

Number of substrate molecules Number of product molecules formed in 30s

20

What is the effect of changing the substrate concentration?

Can you explain why?Effect of changing temperatureChoose one enzyme and 20 substrate molecules.Set the temperature to 5 degrees and leave the other settings the same.Let the animation run for 30 seconds and then record the number of product molecules formed.Repeat the experiment but increase the temperature.

Temperature /0C Number of product molecules formed in 30s

5

What is the effect of changing temperature on this enzyme?

Can you explain why?

Effect of changing pHChoose one enzyme and 20 substrate molecules.Set the temperature to 25 degrees and leave the other settings the same.Set the pH to 1Let the animation run for 30 seconds and then record the number of products molecules formed.Repeat the experiment but increase the pH.

pH of experiment Number of product molecules formed in 30s

1

4

7

11

14

.What is the effect of pH on this enzyme?

Can you explain why?Experiments involving Enzymes

© Nuffield Foundation / Biosciences Federation 2008 • Downloaded from Practicalbiology.org

Investigating the effect of pH on amylase activityThis practical allows you to:

· discover how pH affects the rate of an enzyme controlled reaction· evaluate the experimental procedure

Procedure Wear eye protection when handling the iodine solution.

a Place single drops of iodine solution in rows on the tile.b Label a test tube with the pH to be tested.c Use the syringe to place 2 cm3 of amylase into the test tube.d Add 1 cm3 of buffer solution to the test tube using a syringe.e Use another syringe to add 2 cm3 of starch to the amylase/ buffer solution. Start the stop clock and leave it on throughout the test. Mix using a plastic pipette.f After 10 seconds, use the plastic pipette to place one drop of the mixture on the first drop of iodine. The iodine solution should turn blue-black. Squirt the rest of the solution in the pipette back into the test tube.g Wait another 10 seconds. Then remove a second drop of the mixture to add to the next drop of iodine.h Repeat step g until the iodine solution and the amylase/ buffer/ starch mixture remain orange.i You could prepare a control drop for comparison with the test drops. What should this contain?j Count up how many iodine drops you have used, each one equals 10 seconds of reaction time.k Repeat the whole procedure with another of the pH buffers or pool your results with others in your class.l Collect repeat data if there is time.m Plot a graph of time taken for starch to break down against pH.ORCalculate the rate of the reaction by calculating 1 ÷ time. Plot rate of reaction against pH.

Results

Graph

QuestionsIt is important to add the buffer to the enzyme before adding the starch. Why is this?

How does a control help you with the colour comparison?

Are there any anomalies or inconsistencies in your results?

Do you think your results are reliable? How would repeating the investigation help you to check the reliability?

Describe your graph. What is the effect of pH on the enzyme controlled reaction?

Explain how pH affects enzyme reactions.

How could you improve this investigation?

Investigating the effect of changing concentration on catalase activityThis practical allows you to· investigate the effect of substrate concentration on the activity of catalase

· evaluate a practical protocol

ProcedureWear eye protection and protect clothing from hydrogen peroxide. Rinse splashes of peroxide and pureed potato off the skin as quickly as possible.

a Use the large syringe to measure 20 cm3 pureed potato into the conical flask.b Put the bung securely in the flask – twist and push carefully.c Half-fill the trough, bowl or sink with water.d Fill the 50 cm3 measuring cylinder with water. Invert it over the trough of water, with the open end under the surface of the water in the bowl and with the end of the rubber tubing in the measuring cylinder. Clamp in place.e Measure 2 cm3 of hydrogen peroxide into the 2 cm3 syringe. Put the syringe in place in the bung of the flask but do not push the plunger straight away.f Check the rubber tube is safely in the measuring cylinder. Push the plunger on the syringe and immediately start the stop clock.g After 30 seconds, note the volume of oxygen in the measuring cylinder in a suitable table of results.h Empty and rinse the conical flask and measure another 20 cm3 pureed potato into it. Reassemble the apparatus, refill the measuring cylinder, and repeat from d to g with another concentration of hydrogen peroxide. Use a 100 cm3 measuring cylinder for concentrations of hydrogen peroxide over 20 vol.i Calculate the rate of oxygen production in cm3/ s.j Plot a graph of rate of oxygen production against concentration of hydrogen peroxide.

Results

Graph

QuestionsApart from oxygen, what product is made when hydrogen peroxide breaks down?

Identify any anomalies or inconsistencies in your results.

Describe the shape of the graph.

Explain the shape of the graph in relevant biological terms.

Describe any technical difficulties you had with this apparatus and explain how these could be overcome.

Describe how you would extend this investigation to provide more evidence/ data to support your understanding of enzyme-controlled reactions.

Past Paper Questions