To investigate the optimum concentration of an enzyme in an enzyme controlled reaction

On the flat plateau region on my graph the enzyme has reacted with all of the substrate so no matter how much more enzyme is added you will not get any more reaction. If any increase is required, the amount of substrate must be increased. The diagram below shows this occurring.

Variables: I will be changing the concentration of the tissue source celery of catalase.

We will keep the same:

* Volume of Hydrogen Peroxide

* Temperature (22 degrees centigrade)

* Light conditions

* Batch of celery

* Volume of source tissue

* Time over which we measure the oxygen

Pre-testing: We carried out a series of experiments before our main one to finalise our method for our investigation. We decided to use Catalase enzyme on its substrate Hydrogen Peroxide because we have used it in a series of practical. This reaction gives us instant measurable results that are reliable. It also allows us to get a range of results. The only other enzyme that we had used in previous experiments was amylase. This reacts with starch the only way of getting a measurable result was to look at the colour change this would mean that our results would not be reliable. Liver tissue would have been the best to use that contained catalase but this was unsuitable because of health and religious reasons. The next best source of catalase is celery, which we chose to use. We decided to measure the oxygen given off by using a burette because it is glass and narrow this would make our results reliable. It also has clear marking for us to read off. The only problem with this was that it has a gap near the tap. We placed different amounts of Catalase in a measuring cylinder with Hydrogen Peroxide and measured the amount of foam produced. We measured the foam to give us a guide but this was too inaccurate to use in our main investigation. We decided to use 10ml of Hydrogen Peroxide and 10ml of Catalase this is our 100% concentration. We will dilute the Catalase enzyme. We will measure the amount of oxygen in 60 seconds it gives us a large volume of oxygen and allows us to be precise

Method:

Burette

Boiling tube

Delivery tube

Bung

Shringe

Measuring Cylinder

Trough

Stand

Clamp

Stopclock

We set up the apparatus as above. We filled the trough and burette up with water making sure that the burette was totally full we then turned it upside down and placed the end into the trough. We placed the end of the delivery tube under the burette. We then got 10ml of Hydrogen Peroxide and placed it into a boiling tube. We measured out 4ml of catalase using a shringe to be accurate and then placed this in a measuring cylinder then we added 6ml of distilled water and mixed them together. This is the 40% concentration. Although the celery contained water, we used it as our 100%. We placed this into the boiling tube with the Hydrogen peroxide and placed the bung on top we started our stopclock. After 60 seconds, we read off how much water had been displaced by the oxygen. We repeated this concentration of enzyme five times making sure that the results were consistent this would mean that our results would be reliable. Onto each result, we added 3.6 this was the amount near the tap of the burette. We measured this by filling up this small area with water and pouring it into a measuring cylinder to measure it. If any results did not fit into our pattern, we repeated then them as this may have been caused if the clock was started at the wrong point. We repeated this for each concentration between 30 and 100%, we did not go below 30% because the celery already contained water, which would have affected our results. When all of our results were collected and plotted a graph. We found that the optimum concentration was between 90 and 100% so we repeated this experiment for 91 to 99%.

Results

Concentration of Celery Extract

Volume of Oxygen (ml):

2

3

4

5

Average

(ml)

30

6.4

6.8

7.1

6.9

7.2

6.88

40

9.1

0.3

1.8

2.6

1.3

1.02

50

4.4

4.4

4.4

4.5

5.0

4.54

60

7.8

8.0

7.4

7.8

7.6

7.72

70

4.9

5.3

5.9

5.7

6.8

5.72

80

22.3

21.9

21.8

21.5

34.6 22.5

22.00

90

26.5

27.6

27.2

26.9

26.5

26.94

00

28.5

27.9

28.2

28.4

28.3

28.26

Concentration of Celery Extract

Volume of Oxygen (ml):

2

3

4

5

Average

(ml)

90

As above

91

26.5

27.6

26.8

26.6

26.8

26.86

92

27.2

27.9

26.7

26.9

27.0

27.14

93

28.1

27.7

27.8

27.9

27.7

27.84

94

27.8

28.4

28.5

28.3

28.6

28.32

95

28.0

28.2

27.9

28.6

28.5

28.24

96

28.7

28.2

28.4

28.5

28.6

28.48

97

28.3

28.1

28.4

28.2

28.5

28.30

98

28.5

28.3

8.6 28.2

28.4

28.5

28.36

99

28.4

28.2

27.8

28.3

28.5

28.24

00

As above

The numbers in red are anomalous results we repeated them again as they did not fit in with the other results I did not include them in any other of my calculations

Conclusion: My graph shows the relationship between the concentration of enzyme and the rate of reaction. The rate of reaction is the amount of oxygen given off from the reaction in 60 seconds.

From my narrow range graph, you can see that the optimum concentration of this reaction is 95%.

I have included some detailed information about this particular reaction in my prediction. This can be found on page 1.

My prediction graph agrees with my final graph. The first part of the graph is an upward slope. It shows that as the temperature rises so does the amount of oxygen given off. This is what I had predicted.

The flat region of my graph shows that the enzyme is the same amount as substrate and the reaction is at its optimum or highest rate. No matter how much more enzyme is added there will be no more oxygen produced because there is not enough substrate.

I could not have predicted the optimum concentration because that was the aim of the experiment although I would have expected it to be lower. However, because we used celery this contains water, which would mean that the enzyme had been diluted.