An Enzyme is any one of many specialised organic substances, composed of polymers of amino acids, that act as catalysts to regulate the speed of the many chemical reactions involved in the metabolism of living organisms.

Kate Massey Enzyme Experiment 26/06/02

Introduction

An Enzyme is any one of many specialised organic substances, composed of polymers of amino acids, that act as catalysts to regulate the speed of the many chemical reactions involved in the metabolism of living organisms. Those enzymes identified now number more than 700.
Enzymes are classified into several broad categories, such as hydrolytic, oxidising, and reducing, depending on the type of reaction they control. Hydrolytic enzymes accelerate reactions in which a substance is broken down into simpler compounds through reaction with water molecules. Oxidising enzymes, known as oxidises, accelerate oxidation reactions; reducing enzymes speed up reduction reactions, in which oxygen is removed. Many other enzymes catalyse other types of reactions.
Individual enzymes are named by adding ASE to the name of the substrate with which they react. The enzyme that controls urea decomposition is called urease; those that control protein hydrolyses are known as proteinases. Some enzymes, such as the proteinases trypsin and pepsin, retain the names used before this nomenclature was adopted Structure and Function of an Enzyme
Enzymes are large proteins that speed up chemical reactions. In their globular structure, one or more polypeptide chains twist and fold, bringing together a small number of amino acids to form the active site, or the location on the enzyme where the substrate binds and the reaction takes place. Enzyme and substrate fail to bind if their shapes do not match exactly. This ensures that the enzyme does not participate in the wrong reaction. The enzyme itself is unaffected by the reaction. When the products have been released, the enzyme is ready to bind with a new substrate.

Enzymes are highly specific in the reaction catalysed. Some enzymes catalyse the transformation of one particular type of substrate molecule or, at most a very restricted group of substrate molecules: Some catalyse only one type pf chemical change. This degree of specificity distinguishes enzymes from all other types of catalyst.

The specificity of enzymes is due to the configuration of the active site. This idea was originally developed as the ‘lock and key’ hypothesis and substrate is the key that fits exactly into the enzyme lock

My experiment is to investigate one of the factors the ...

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My experiment is to investigate one of the factors the affects the breakdown of hydrogen peroxide, the enzyme, which is found in potato, catalyses the reaction.

Catalase

2H2 O2 2H2O + 02

(Substrate) enzyme (products)

Catalyse behaves in a similar manner to the digestive enzymes.

Safety

I will have to be very careful whist using hydrogen peroxide, as it is a corrosive chemical and also a bleaching agent so I will wear protective garments and safety goggles at all times. To resist any hazards.

Variables

Susceptibility to temperature change
Susceptibility to pH changes
Enzyme concentration
Substrate concentration

Substrate

I am going to vary substrate concentration and try to control all of the other variables.

I shall be varying the amount of water and hydrogen peroxide and therefore will be keeping all other variables in the same order to make sure that it is a fair test. I will keep my variables the same by ensuring that I have implied the same strategy for each of the results taken. The amount of the enzyme must stay the same at 2cm squared, which I will measure using a pipette.

Fair Test:

To make sure that it is a fair test I will make sure that the following variables are controlled.

I will make sure that the temperature of the enzyme stays at 37º, this is crucial as this is the best temperature that enzyme will work at (as it is the temperature of the human body) if it differs even by a very small amount it could change the results reliability. Using a water bath, which will ensure that it has a constant temperature of 37º C, could also prevent this.

I must also ensure that the pH level stays the same throughout the experiment as again this could drastically change the reliability of it, I will make sure that it stays at Ph 7 (the ideal pH for an enzyme to work at as it is the pH inside the human body) by using universal indicator paper which will tell me the pH level by the colour that it will change.

I must also try to use the same producer (potato) of the enzyme for every experiment I do as different potatoes may differ slightly. Also I must measure the enzyme extremely carefully so that it is 2cm² exactly. I will make sure of this by using a pipette and making sure that it is on the correct level.

Diagram

Prediction:

For a fixed enzyme concentration, the rate of reaction is affected by increase in substrate concentration. An increase in the number of substrate molecules increases the number of successful enzyme-substrate collisions, so the rate of reaction is faster. At higher substrate concentrations the active site of every enzyme is occupied at every given moment. Any added substrate molecules have to ‘wait’ until an existing enzyme-substrate complex dissociates to release products and free enzyme. Consequently adding more substrate has no effect on the rate of the enzyme catalysed reaction. If further enzyme is added, the reaction rate can increase again.

Apparatus

Enzyme

Side arm tube

Graduated tube

Delivery tube

Trough (with water)

Hydrochloric acid

3 syringes

Stopwatch

Thermometer

Bowl

Measuring cylinder

Bung

Method

From the graph that I have produced it is easy to see that the higher the concentration of hydrogen peroxide, the more time taken and the higher the rate of reaction. Which proves my prediction correct.

Evaluation

Although I conducted the experiment as accurately as I thought possible, there were still a few floors that I feel could have been prevented and that I feel could have interfered with the accuracy of the results.

First off there was a short delay in the starting of the stop watch as there were a few uncertainties in which one of us was to set off the stop watch in the first experiment we did, although the result would of only been out by a few seconds this has still affected the accuracy.

We also had to make sure that the bung was securely inside of the test tube straight after the hydrogen peroxide had been added, this was because it was the exact time that the reaction was taking place.

After conducting the experiment we realised that to of produced a steadier se of results it may have been easier to of introduced a water bath to the experiment this would have added more stability to the experiment and ensured that our results were not anomalous.

The week after we decided to do a second set of results as we had a few anomalies but unfortunately due to the void in time we were unable to use to same potato. This was a source of error as the concentration of catalase in the potato may have been different which may have caused an inconstant rate of reaction. Despite this the second time we did the experiment proved to be of more success than the first. Which we were extremely pleased about.

The evidence that I have obtained is sufficient enough to support the conclusion that I have come to about the reaction of the enzyme and hydrogen peroxide. As I have conducted the experiment as accurately as I could and with the method that I had used.