Analysis of the Decomposition Rate of Hydrogen Peroxide With Catalase As a Catalyst

Aim: To measure the rate of decomposition of Hydrogen Peroxide with
Catalase from a Yeast solution using PH as a variable.

Hypothesis: The enzyme Catalase speeds up the Hydrogen Peroxide
decomposition as its active sites match the shape of the Hydrogen
Peroxide molecule. This process will only work at certain PH levels as
the Enzyme sites may become disfigured at extremes. Logic suggests
that Catalase will work well at PH7 Neutral, but due to the nature of
Catalase removing Hydrogen Peroxide from human body cells a slightly
acidic solution might work just as well.

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This is based on the Key and Lock principle of the enzyme;

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When various different PH values are present the shape of the Lock of
the Enzyme varies, this can cause a slower rate of reaction, or in the
event of the lock become completely deformed no reaction.

Catalase is present in the peroxisomes of nearly all aerobic cells. It
serves to protect the cell from the toxic effects of hydrogen peroxide
by catalysing its decomposition into molecular oxygen and water.

Catalase

Hydrogen Peroxide---------------------->Water + Oxygen

Catalase

2H2O2------------------->2H2O+O 2

Apparatus Required:

Ÿ Gas Syringe,

Ÿ Metal Stand,

Ÿ Yeast (Catalase),

Ÿ Hydrogen Peroxide,

Ÿ Beakers,

Ÿ Syringe,

Ÿ Stop clock,

Ÿ PH Buffers,

Ÿ Conical flask with Bung including opening for syringe and gas
syringe.

Plan:

Add 5cm3 of yeast into the conical flask, as this gives an easily
measurable volume with little room for error that would occur in
larger volumes, we also only want to measure the decomposition with
the amount of oxygen given off and therefore don't need to notice the
visual changes present in larger experiments. Add 5cm3 of PH buffer
into the conical; flask and mix with Yeast. Insert Syringe filled with
5cm3 of Hydrogen Peroxide into syringe opening, slowly add the H2O2
into the yeast and time 30 seconds before measuring the amount of
Oxygen produced on the Gas Syringe. Repeat the experiment at least
twice for each PH buffer available. Repeating the experiments several
times will help to produce better and more accurate results as any
inaccuracies in one experiment should be compensated for by the other
experiments.

I am using yeast Catalase as opposed to Catalase from apples, potatoes
or liver because it is easier to get the desired concentration of
catalase by simply measuring it off. To ensure this is a fair test all
the variables except for the PH buffer must be kept the same for all
the experiments. Therefore it is necessary to make sure that at the
start of all the experiments all factors are the same for each,
humidity can be easily controlled with a room temperature water bath,
but variables like Catalase concentration due to its very nature
cannot be kept exact, but to limit variation the same batch of yeast
must be used on the same day in the same session.

There is a slight delay between pouring the concentration of Hydrogen
Peroxide into the yeast, and starting the stopwatch. This is not
possible to completely sort out but by working in groups one can
partially rectify the situation.

Hydrogen Peroxide is an Irritant and therefore all safety precautions
must be taken, including the use of Goggles and Lab Coats, also if the
Method is carried out conscientiously Safety is improved.

Diagram:

Results:

All readings of the amount of oxygen given off are given after 30
seconds and to the nearest integer;

PH

Reading 1 ( )

Reading 2 ( )

Reading 3 ( )

Average Reading ( )

8

10

17

15

14

7

17

20

19

19

6

18

21

22

20

5

8

18

17

14

4

3

16

14

11

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This graph shows the Decomposition of Hydrogen Peroxide at different
PH levels with Catalase acting as a Catalyst.

Conclusion: Overall the rate of Decomposition is very similar to my
predicted graph; peaking at about PH6, However the results I have
gathered suggest that the Key and Lock in Catalase is preferable to
slightly acidic solutions as opposed to alkaline solutions , this
theory could be proven by carrying out H2O2 decomposition
investigations using different sources of Catalase.

Evaluation: The experiment was successful in the fact that it proved
my theory laid out in my hypothesis, it could have been improved by
adding a few factors; A better overall result would be obtained by
repeating the experiment more times because any errors in one
experiment should be compensated for by the other experiments.

Using more PH levels should have produced a smoother curve on the
graph. As mentioned above the use of different sources of Catalase
could also have been implemented