Investigating the effect of substrate concentration on the rate of an enzyme controlled reaction.

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Investigating the effect of substrate concentration on the rate of an enzyme controlled reaction

Aim: to find the effect substrate concentration has on the rate of reaction of an enzyme controlled reaction.

I have decided to measure the rate of reaction of the break down of hydrogen peroxide when using catalase. I have decided to use this reaction for the following reasons: from preliminary work I found that this reaction occurs at a speed suitable for measuring with the equipment available at school. This experiment is also suitable as I am familiar with it from doing similar experiments in GCSE biology.

Introduction

Enzymes have the ability to catalyse an experiment, for this reason they are often used to speed up reactions which don’t go fast enough naturally. It speeds up a reaction by lowering the activation energy(Ea) thus meaning more collisions between reactants result in successful reactions taking place:

This diagram shows that by adding a catalase we lower the activation energy consequently increasing the number of particles able to react successfully.  What the diagram doesn’t demonstrate is the fact that the reaction finishes faster but the same amounts of products are produced.

The substance that the enzyme acts on is called the substrate. In the reaction I am using in my experiment the substrate of the catalase is hydrogen peroxide. The function of the enzyme can be explained by the lock and key theory:

Picture from: www.ghs.gresham.k12.or.us/science/ps/

Diagram 1 on pg 1 shows the lock and key theory of how enzymes work, we must also consider the induced fit model though as this may be how catalase enzyme works:

Both theories are similar in that at stage 2 the enzyme and substrate join to form an enzyme substrate complex, but are different because the substrate and active site of the enzyme are complimentary in the lock and key theory whereas in the induced fit theory the active site is a similar shape to the enzyme and it changes slightly to allow the enzyme substrate complex to form.

Hydrogen peroxide breaks down naturally but for the purposes of this experiment I am using a catalyst to speed up this process. The presence of enzymes makes the activation energy decrease by weakening the bonds of the substrate meaning that not as much energy is needed to break the bonds and for new products to be formed.

The enzyme I will use is a breaker enzyme it will perform the catabolic reaction of forming O2  and H 2 from hydrogen peroxide. This type of enzyme is present in living organisms and is used in the process of digestion for example.

Prediction:

I hypothesise that the higher the concentration of the substrate, the higher the rate of reaction.

For a substance to react, collisions must occur between reactants, that is the molecules of Hydrogen Peroxide must collide with the yeast cells containing the catalase in order for there to be a reaction. By increasing the concentration of the substrate, we are increasing the amount of substrate per unit thus increasing the likelihood of collisions occurring. If we increase the number of collisions per second we will also increase the rate of reaction.

In addition, I think that there will be a plateau effect due to the fact that eventually there will not be enough catalase molecules to provide active sites for the catabolic reaction of the break down of the Hydrogen Peroxide and after a point the rate of reaction will stop increasing and increasing the concentration of the substrate will no longer have an effect.

Plan

Before carrying out the experiment and deciding the final details of how I will do this I have done some preliminary work to determine the best method of testing the hypothesis.

Preliminary work: We decided that to find the rate of reaction we are going to see how much gas is produced in a set amount of time. We therefore need a way of collecting gas, we decided on two methods and then we tested their accuracy:

Method 1:

Used: 5 ml yeast (containing enzyme catalase)

        1 ml Hydrogen Peroxide.

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Results: 3ml of O2 in 60 secs

          =0.03ml/s

Method 2:

Used: 5 ml yeast

        1ml Hydrogen Peroxide

Results: 5 ml O2 in 60 secs

        = 0.08 ml/s

Conclusions

From these results you can see that method 2 collected 2ml more gas in 60 seconds than method 1 therefore I conclude that using a gas syringe to collect the oxygen from the reaction is more effective than method 1, using an up turned measuring cylinder. The reasons I think for the gas syringe being more effective than the measuring ...

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