The Effect of Substrate Concentration on the Activity of the Enzyme Catalase

The Effect of Substrate Concentration on the Activity of the Enzyme Catalase
The aim of this investigation is to find out if changing the substrate
concentration will have any effect on the activity of the enzyme
activity.
Enzymes are a very important for all living things. This is because
they are essential to life as they are used in virtually every
metabolic reaction. They are designed to work within a temperature
range of 5-40ËšC, they do this as if it was any higher it would damage
living cells.

We call an enzyme a Biological Catalyst. A catalyst is a molecule
which speeds up a reaction. They are very important as if they were
not there reactions in cells would be to slow to support life.

They speed up reactions by lowering the activation energy needed in
the reaction. The activation energy is the energy needed to get a
reaction going e.g. activation energy is like pushing a rock to the
top of a hill and then pushing it off the top. The activation energy
is the energy needed to get the rock to the top of the hill. When it
is pushed of the top it no longer needs any help and it does it by
itself. The diagram below explains activation energy: -

Activation energy graph without enzyme

This graph show the energy with is needed to get a reaction going i.e.
activation energy.


Activation energy graph with enzyme

This graph shows what happens to activation energy when an enzyme is
added to the reaction. You can clearly see the difference and this
shows why enzymes speed up (catalyse) reactions.



There are two types of enzyme reaction, these are: -

* Anabolic - involved in synthesis

* Catabolic - involved in breakdown (yeast and hydrogen peroxide is
this type of reaction)

One amazing thing about an enzyme is that when it is used in a
reaction it will come out after the reaction exactly the same it was
when it went in.

All enzymes are globular proteins but not all globular proteins are
enzymes. They have a three dimensional structure with hydrophilic
R-groups arranged on the outside to ensure that the molecule is
soluble.

Enzymes are specific, this means that each enzyme will only work with
one reaction or one small group of reactions. This because each enzyme
has an active site this is a cleft in the enzyme surface where
substrate molecules can bind. The substrate molecule has to be the
correct shape for the enzymes active site or otherwise it will not
fit. This is the lock and key hypothesis. If the substrate does not
fit to the active site it tells you that it is not the specific enzyme
for the active site.



Fisher's lock and key hypothesis above (diagram from Biological
Science)

It is not enough for the substrate just to fit into an active site it
need an attractive force to keep it in place. The attractive forces
are

* Electrostatic attraction between oppositely charged groups

* Hydrogen bonding

* Permanent dipole-permanent dipole forces

* Instantaneous dipole-induced dipole forces

Once an enzyme molecule and a substrate molecule have joined together
it is called an enzyme/substrate complex.

In this investigation enzyme catalase accelerates the breakdown of
hydrogen peroxide into water and oxygen. This catalase-mediated
reaction is extremely important in the cells because it prevents the
hydrogen peroxide building up in the cells. Hydrogen peroxide is a
strong oxidizing agent which tends to disrupt the delicate balance of
cell chemistry.

The Plan

Variables

When you investigation enzyme activity there are several variables you
can change or modify, these are: -

* Temperature

* Ph level

* Substrate concentration

* Enzyme concentration

* Inhibitors

Temperature - this is where you would keep the same amount of
substrate and enzyme but change the temperature. You would have a
large range of temperatures (probably 10ËšC to 60ËšC). This is so you
can see when the enzyme is denaturized at 40Ëš and then see the enzyme
activity drop.

Ph level - this is where you would test the same amount of substrate
and enzyme but change the ph level. You would probably use a wide
range of ph levels to see how it behaves in an acid, neutral and an
alkaline solution.

Substrate concentration - this is where you would use change the
concentration of the substrate and keep the enzyme concentration the
same. Again you would want to use a wide range of concentrations so
you would get a wide range of result. Then from these you could draw
conclusions.

Enzyme concentration - this is basically the same as substrate
concentration but you keep substrate the same and change enzyme
concentration. As with substrate concentration you would want to use a
wide range of concentrations. This is so you would get a wide range of
results. In which you could draw conclusions.

Inhibitors - this is where you use the same enzyme and substrate
concentration but change the amount of inhibitors used. I.e. you could
have 0% inhibitors to 100% inhibitors. This would show you what affect
in inhibitors have on enzyme activity.

Catalase Enzymes

Catalase enzymes are enzymes which speed up reactions. Catalase
enzymes are some of the most potent catalysts known. The reactions it
catalyses are crucial to life. The catalase enzymes convert Hydrogen
Peroxide, a powerful and potentially harmful oxidizing agent into
water and oxygen. This is very important to life as if it did happen
your body would allow Hydrogen Peroxide to build up in the cells. This
would cause harm to your body. So the body has catalase enzymes which
break up Hydrogen Peroxide in oxygen and water. One example of a
Catalase enzyme is Yeast. Yeast is the catalase enzyme which is going
to be used in this investigation.

In this investigation it will look at how Substrate Concentration
affects enzyme activity.

What enzyme and substrate?

For the investigation the enzyme and substrate that will be used is
Hydrogen Peroxide and Yeast. Hydrogen is the substrate and yeast is
the enzyme. The formula for the reaction is:-

Catalase Yeast added (enzyme)

Hydrogen Peroxide = Water + Oxygen



2H 2 O 2 = H 2 O + O 2



When hydrogen peroxide is left it will slowly decompose naturally into water and oxygen just from energy from the sun. This is why it is rarely kept in a clear bottle as it would otherwise decompose into water and oxygen. For this to happen it would take a very long time, this is why an enzyme was added. The enzyme acts as a catalyst and speeds up the reaction causing the water and oxygen to be released a lot quicker than it would take to naturally decompose.



The enzyme can speed up the reaction rate of the hydrogen peroxide because yeast enzyme fits the hydro peroxide active site. When the yeast binds with the substrate it creates an enzyme-substrate complex. The enzymes interaction with substrate causes it to break down into two product molecules (water and oxygen) leaving the yeast enzyme unchanged.



What must be kept the same?



To ensure that the investigation is reliable there are several steps which have to be taken to ensure this. These are:-

Â? Keep enzyme concentration the same

Â? Stir the yeast

Â? Repeat test to increase reliability

Â? Use same enzyme concentration in each test

Prediction

The reaction will start very quickly with as enzyme and substrate are
mixed. When the reaction starts bubbles of oxygen will be produced.
The largest volume of oxygen will be recorded in the first minute than
any other minute. This means the initial speed will be faster in the
first minute than any other minute. When substrate concentration is
increased the speed of the initial reaction will increase. This tells
us that substrate concentration is proportional to the initial rate
i.e. as substrate concentration increase the initial rate increases
and when initial rate increase substrate concentration increases. In
the later stages of the reaction the reaction will get slower and less
gas will be produced until in stop completely. This will be cause the
reaction not to be proportional any more.

This means the results which should be expected from the experiment
are

* Very high volumes of oxygen when there is a high substrate
concentration

* Then very low volumes of oxygen when there is low substrate
concentration

This will mean the curve on the graph will be steep at the beginning
where the reaction is at its fastest but as the reaction goes on it
will level off

The graph should look like this: -


Scientific knowledge can be used to explain why the above prediction
was correct. The initial reaction rate will be higher with a higher
substrate concentration and lower with a lower substrate
concentration. This is because at a higher substrate concentration
there will be more hydrogen peroxide (substrate) molecules available
to collide with the enzyme (yeast) active sites. This means at a lower
substrate concentration the rate of reaction will be lower because
there will be less substrate so it will take them longer to collide
with the enzymes active sites and bind with them.

The Effect of Substrate Concentration on the Activity of the Enzyme Catalase 9.2 of 10 on the basis of 3303 Review.