Background On Enzymes

Background On Enzymes

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Background On Enzymes

Enzymes are biological catalysts. They speed up the chemical reactions
which go on inside living things. Without enzymes reactions would be
so slow that eventually life would grind to a halt.

There are many different types of enzymes and each of them is
extremely efficient at doing their job. For example, some of the
reactions which take place in our cells, e.g. the liver, produce a
by-product called hydrogen peroxide. Hydrogen peroxide is very
poisonous so it must be gotten rid very quickly. An enzyme called
catalase breaks the hydrogen peroxide down into two harmless
substances, water and oxygen.

Enzymes have 5 important properties:

1. They are always proteins- this is why we need protein in our diet.

2. They are specific in their action- this means that each enzyme
controls one particular reaction, or type of reaction. Therefore
maltase will only act on maltose and sucrase on sucrose.

3. They can be used over and over again- this is because they are not
altered by the reaction in which they take part. However an enzyme
molecule will eventually run down and has to be replaced.

4. They are destroyed by heating- enzymes like all proteins are
destroyed by heating. This is called denaturation. Most enzymes stop
working if the temperature rises to about 45°C - destroys active site.

5. They are sensitive to pH- the term pH refers to the acidity of the
alkalinity of a solution. Most enzymes work better in neutral

How do enzymes work? Molecules are constantly moving about and bumping
into each other. When a substrate molecule bumps into a molecule of
the right enzyme it fits into a depression on the surface of the
enzyme molecule ( a bit like a jigsaw puzzle.) this depression is
called the active site. The reaction then takes place and the
molecules of product leave this active site, freeing it up for another
substrate molecule.

The active site of a particular enzyme has a specific shape into which
only one kind of substrate will fit rather like a key fits into a

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lock. This is why enzymes are specific in their action. Therefore when
an enzyme is denatured by heat, the shape of the active site changes
so that the substrate can no longer fit into it.

Enzymes are used for many different things for instance:

Proteases are use for tenderising meat, skinning fish, removing hair
from hides and breaking down proteins in baby food.

Amylase is used for converting starch into sugar, in fruit juices,
chocolate and other food products.

Cellulase is used in the breaking down of cellulose, for softening
vegetables, removing the seed coat from cereal and extracting agar
jelly from seaweed.

Catalase is used for releasing oxygen from hydrogen peroxide and in
making foam rubber from latex.

Aim: Experiment to show how an increase in the amount of enzyme
affects the rate of enzyme action.

Prediction: As the surface area is increased the amount of enzyme
available is also increased. In other words there are more active
sites available to catalyst the reaction. Therefore I predict that as
the surface area increases the more oxygen bubbles are produced.

Apparatus: Potato Chips = Catalase



Measuring Cylinder

Tile and Knife

Wet Paper Towel

pH Paper


Side-arm Test-tube




Stop Watch

Safety: Make sure you are wearing gloves and that none of the Hydrogen
Peroxide solution touches you skin or clothes as it is corrosive.

Make sure that you watch carefully what you are doing with the knife
so that you don't cut yourself.

Make sure that all the bags are outside of the lab so that no one
trips over.

Make sure you wear goggles so that the hydrogen peroxide can not get
into your eyes.


Preliminary Experiment: Firstly I am going to do a preliminary
experiment in order to find out the volume of H2O2 needed to cover the
chip, however I will be using H2O. Also I will do a preliminary
experiment to find out the length of the chip I should use to be
completely covered.

Real Experiment: Apparatus set up as in diagram. I am going to collect
my 6 chips and and my other apparatus need for the experiment. I am
then going to put the right volume, found out from preliminary
experiment, of H2O2 into side-arm test-tube and connect it to a
test-tube containing H2O.

I am then to put my first chip into the test-tube containing H2O2 and
put a bung on the top. Then I am going to leave the chip for about a
minute in order to let it settle. Then I will time for 5mins while
counting the number of bubbles produced in the test-tube containing
the H2O. Then I will repeat this experiment in order to make it a fair
test and to get the most accurate results possible.

In order to do the experiment described in the aim and to see wether
my prediction is correct, I will do the experiment again but this time
I will increase the amount of exposed enzymes by cutting up my chip
into 2 then 4,8 16 and 32 pieces. I will repeat these experiments in
order to make the experiments more accurate.

I will use a knife and cutting tile to cut my potato.

Fair Test: In my intordution I stated that pH and tempertature affect
the activity of enzymes. Therefore during the experiment I will have
to control the temperature and pH of my solution in order to keep my
enzymes from denaturing.

I will also need to use the same volume of hydrogen peroxide and the
same length chip throughout the entire experiment.

Errors, Analysis and Evaluation: As the experiment became more
concentrated more bubbles were produced due to the collision theory,
increased movement inside the test-tube which means more oxygen
produced. This is shown on my graph as the line rises as more pieces
are cut. However I felt that the results could have been more accurate
if it wasn't for the fact the pieces of potato overlapping, a thick
froth started to form and the bubbles became increasingly difficult to
count. There were also a lot of distractions on the day of the
experiment as it was open day and there were parents walking around
and it became hard to concentrate on counting the bubbles and watch
the stop watch at the same time.

I was expecting my graph to form a plateau as I expected that there
would not be enough H2O2 for the active site, this is a limiting
factor, and the reaction would start to slow down and eventually stop
due to the lack of H2O2. My prediction was proven to be correct as the
increase in surface area did mean that the number of bubbles
increased. Which means that as the surface area was increased there
were more active sites to lock onto the H2O2 which means more H2O2 was
split therefore more oxygen bubbles were released. If I did the
experiment again I would use a sharper knife as the knife I had was
blunt, I would make sure that my pieces of potato all cut straight as
some of my were cut diagonally, I would also ensure that my syringe
did not have an air lock init and maybe use a more hydrogen peroxide
and more pieces of potato so that the experiment could have carried on
for longer and so that I would have gotten a better graph. I would
also remember to take down the temperature of the room and the pH of
the solution as I forgot and it was one of my constants in order to
keep my experiment a fair test and to stop the enzymes from
denaturing. It would be interesting if next time I could use a
different vegetable to see what happens.

Conclusion: From the experiment I found that my prediction was correct
and the higher the concentration and the larger the surface area are
the more oxygen bubbles are produced, due to the active sites locking
onto the hydrogen peroxide molecules and splitting them.
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