An Investigation to see what factors will affect the rate of an enzyme.

Biology Coursework

Section 1

Planning

Introduction

Enzymes exist in all living things. They are composed of amino acid, polymers, carbohydrases etc. and are produced in living cells. A cell contains hundreds of enzymes that break down different things. Most people think enzymes are only digestive enzymes but there are many other different enzymes, for example, catalase, which is the enzyme I will be studying for my experiment. Catalase is an enzyme found in food such as potato and liver. It is used for removing hydrogen peroxide from the cells. Catalase speeds up the decomposition of hydrogen peroxide into water and oxygen. It is able to speed up the decomposition of hydrogen peroxide because of the bonds of the hydrogen peroxide molecule. This type of reaction where a molecule is broken down into smaller pieces is called an anabolic reaction. Hydrogen peroxide can be lethal in a human body if it builds up. When catalase reacts with hydrogen peroxide, oxygen and water are produced. These can be used in the body. The formula for this is:

Catalase

Hydrogen peroxide oxygen + water

Hydrogen peroxide = Water + Oxygen
2H2O2 2H2O O2

The investigation

I have been asked to investigate the factors that can affect the rate of an enzyme. I think a number of things can affect the rate:

Temperature

Pressure

Concentration of hydrogen peroxide
Concentration of Catalase

Enzymes are specific. This means they only control one type of reaction; therefore, I must use one specific enzyme in my experiment. All enzymes are all globular proteins and are all biological catalysts, they increase the rate of a given reaction without being used up, and their presence does not change the nature of the reaction or the product. Enzymes work by having an active site, made from amino acids. Here, substrate molecules will bind with the enzyme and a reaction takes place. The enzyme itself however, is not affected and releases the new chemical after the reaction. After the release of the end product, more substrate molecules can bind with the active site.

In this investigation, I intend to explore one of the factors that affect the rate of enzyme catalysis. After research and careful consideration, I have decided to first look at how a change in concentration could affect the rate of reaction. In order to design a suitable experiment and make a credible prediction, I must first explore more closely how the concentration is likely to affect the rate of catalysis.

Prediction

The concentration is how much of catalase or hydrogen peroxide there is. If there is a greater concentration of enzyme, there is a greater ...

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Prediction

The concentration is how much of catalase or hydrogen peroxide there is. If there is a greater concentration of enzyme, there is a greater chance of the hydrogen peroxide colliding with the catalase and reacting. Hence, I predict the greater the enzyme concentration the more oxygen will be released in the fixed time. I must now conduct an experiment to test my prediction.

Using my information on catalase, it is clear that one of the products of the reaction is oxygen. Therefore, to measure the rate of reaction, I could measure the rate at which oxygen is produced. For this experiment I will need:

Potato as the source of catalase
Hydrogen peroxide (2 m)
A glass syringe to measure the amount of oxygen produced.
A stopwatch
Conical flask for the two reagents to react in
Bung and delivery tube
Clamp stand and a clamp to hold the apparatus in place
A measuring cylinder to measure out the correct amount of hydrogen peroxide.
Safety Goggles
Cork Borer

Diagram

Here is a diagram of the experiment. I have labelled each of the apparatus.

Preliminary tests.

Before I decided on what amounts of potato and hydrogen peroxide to use I carried out a few preliminary experiments. These helped me to decide what amounts would be best to use. These were very important; as if I had not done them the reaction could be to fast or to slow. If this happened, I would not have been able to record any results. Here are the results of these experiments.

From these experiments, I decided that using potato 3cm long would be the best to use.

The experiment

Here is a systematic plan to carry out my investigation.

Set up the apparatus as shown in the diagram.
Measure 30ml of hydrogen peroxide (2m) in a measuring cylinder
Pour the hydrogen peroxide into the conical flask
Place 1 pieces of potato, 3cm long into the conical flask.
Quickly place the stopper in the flask.
Start the stopwatch immediately.
Time 5 minutes
When the 5 mins are finished, see how much oxygen is produced.
Record the results in my table.
Empty the conical flask and wash out.
Repeat steps 2-10 with a more pieces of potato
Repeat steps 2-11 six times

Fair testing

To make sure this experiment is a fair test, the only factor I must vary must be the enzyme concentration. This means that I have to keep the temperature, pressure, and pH of the substance constant throughout the experiment. In order to ensure accuracy, I will conduct the experiment six times for each number of pieces and take a mean result to plot on the graph. The exact quantities used must first be determined by a preliminary experiment.

Safety

I will make sure my apparatus are safe and secure. I will ensure that no one could be injured from my experiment. I will wear safety goggles to protect my eyes.

Section 2

Obtaining Evidence

Table

Here is a table of results:

Section 3

Analysing

Conclusion

My graph shows a positive correlation, which means that the more potato you use the more hydrogen peroxide is broken down to oxygen. This is because more potato means there are more enzymes. Enzymes work by having an active site, made from amino acids. The substrate molecules bind with the enzyme and a reaction takes place. The enzyme itself however, is not affected and releases oxygen after the reaction. After the release of oxygen, more substrate molecules can bind with the active site. If there are more enzymes, there is more chance of collision between the hydrogen peroxide and catalase. In conclusion, I can see that my prediction was correct. The greater the enzyme concentration the faster the breakdown occurs.

3 Pieces of potato was slightly out of line with the other points. 6 pieces went a lot faster than the rest. The 4 pieces was faster than the 1 piece as there were more enzymes present to collide with the hydrogen peroxide molecules. I expect that if you keep adding more pieces of potato the graph will eventually level off. This is because the hydrogen peroxide will be limited. There will be plenty of enzymes to react with the hydrogen peroxide as you keep adding it. However, as you are not adding more hydrogen peroxide then there wont be any left for the enzyme to react with.

Section 4

Evaluating

Evaluation
My experiment worked well although if I were to do it again I could do certain things differently in order to gain results that are more reliable. If I were to repeat this experiment, I would probably not get exactly the same results.

The 6 pieces of potato was an anomalous result. I.e. it does not follow the same trend as the others. This may have been due to inaccuracies in the way the experiment was performed, or that I need to further my knowledge in order to explain the results. It could also be because I preformed this experiment on different days, which could alter the temperature. I also used different potatoes. It could also be due to the fact that somebody could have left the top off the hydrogen peroxide.

There was a time deference between the times in which the reaction started to the time when I placed the bung into the test tube, which means some oxygen, could have been released. As I only used a ruler to and potato cutter to measure and cut the potato the size of the potato was not accurate.

I am convinced that the results show there is a correlation between the increase in Enzyme concentration and the increased rate of reaction. This correlation would have been easier to work out had my measurements been slightly more accurate. The accuracy of these measurements could be improved by the use of more precise pieces apparatus so there would be fewer margins for error.

To extend this investigation, I could investigate how the temperature can affect the rate of the enzyme, or even the pH.