ii) Temperature:
As temperature increases, molecules move faster (kinetic theory). In an enzyme catalysed reaction, such as the decomposition of hydrogen peroxide, this increases the rate at which the enzyme and substrate molecules meet and therefore the rate at which the products are formed. As the temperature continues to rise, however, the hydrogen and ionic bonds, which hold the enzyme molecules in shape, are broken. If the molecular structure is disrupted, the enzyme ceases to function as the active site no longer accommodates the substrate. The enzyme is denatured.
An enzyme is a protein molecule that speeds up chemical reactions in all living things. Without enzymes, these reactions would occur too slowly or not at all, and no life would be possible. All living cells make enzymes, but enzymes are not alive. Enzyme molecules function by altering other molecules. Enzymes combine with the altered molecules to form a complex molecular structure in which chemical reactions take place. The enzyme, which remains unchanged, then separates from the product of the reaction. Therefore, an enzyme is a sort of biological catalyst. Those enzymes identified now number more than 700.
Enzymes are classified into several broad categories, such as hydrolytic, oxidizing, 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. Oxidizing enzymes, known as oxidizes, accelerate oxidation reactions; reducing enzymes speed up reduction reactions, in which oxygen is removed.
Catalase is present in the paroxysms (micro body organelles that house various oxidation reactions in which toxic peroxides are generated as side products) of nearly all aerobic cells. It serves to protect the cell from the toxic effects of hydrogen peroxide by catalyzing its decomposition into molecular oxygen and water without the production of free radicals (An atom or a group of atoms with an unpaired electron. Radicals are unusually reactive and are capable of causing a wide range of biological damage).
Hydrogen Peroxide = 2H2O2
Hydrogen Peroxide + Catalase = Oxygen + Water
c) Prediction:
Using my existing scientific knowledge, I predict that as I raise the temperature to 30, 35, and 40, this is where we will see the greatest reaction. I predict this because enzymes are designed to react best at the body temperatures of the animals to which they belong. For a mammal, this is around 35-36. Catalysts are used to speed up biochemical reactions in the body.
d) Method:
Apparatus: 1 Pipette
1 Boiling tube
1 Glass escape tube
1 Measuring cylinder
1 Beaker
1g Dried yeast
1 Thermometer
1ml Hydrogen peroxide
e)
i)Variables:
The temperatures of the hydrogen peroxide and the yeast.
(ii) Controlled Variables:
Volume of water in the measuring cylinder: 100.0ml
Times: 5 minutes
Types of liquid: Water, Hydrogen Peroxide, and Yeast solution
Volumes of substances: 1 yeast, 1ml hydrogen peroxide
Room temperature: 25 approximately
Temperatures of mixture: 20oC, 25oC, 30oC, 35oC, 40oC, 45oC. These must be kept as exactly as possible as yeast is very receptive to changes in temperature.
If these variables were altered, it would not be fair test.
To control this variable, the temperature was maintained at a fairly constant level that allowed the enzyme to work effectively (room temperature, approximately 21). This was achieved by using a test tube rack and tongs to handle the apparatus so that the heat from my hands did not affect the Catalase.
f) Table of results:
1% of yeast in 5 minutes:
g) Analysis:
I conclude that my prediction was partly correct. From the graph, you can see the reaction is quicker as the temperature was 33C, but it was slower at 35C and again quicker at 40C, but again slower at 45C. This may be because the catalyst, in this case catalase worked best at that temperature, allowing for more successful collisions between the yeast and hydrogen peroxide molecules.
From the graph, you can see from 20-33oC. I have found out that, as the temperature increases, so does the catalase activity, as it does not take as long to move the same distance, up to a certain point where the activity ceases altogether.
In 33oC, I can see the enzyme is most active and when it starts denature.
I found that the optimum for a catalase is at 33. This is where the greatest number of collisions takes place between the enzyme and the substrate and therefore the highest rate of reaction is.
The rate was higher at the higher temperatures (up to 40) because as the temperature is raised, so is the energy level of the enzymes and substrate molecules. This means that they have more kinetic energy so they collide more often and therefore more reactions take place between them. This, in turn, means that the rate increases as more oxygen (O2) is produced. The enzyme denatured at about 40 because the weak bonds, which hold the molecule into the specific shape for one substrate, are broken. The increase in molecular collisions and vibrations at higher temperatures is great enough to permanently change the shape of the active site. The enzyme is said to be denatured because it can no longer form an enzyme-substrate complex as its active site has been unalterably changed.
I included the anomalies (40C) in my graph because I did not think they would affect the graphs line of best fit. These results may be anomalous because I started the stopwatch too early or too late. This was a very big problem in the experiment and is all explained in my evaluation.
h) Evaluation:
I was a little surprised at some of the results, and if I were to do this experiment again, I would try to discover what it was that gave these findings. I would also do the experiments for every 5oC Instead of every 10oC. I would also measure other variables, to ensure that there cannot be any more fluke results. I would conduct the experiment more times to get a more accurate average.
Although I conducted the experiment as accurately as I could there were many sources of error in the method that I used. Firstly, some help from friends was required to begin the experiment and this lead to a small delay in starting the stop watch. I would have to find a way to be a little more accurate. This would ensure that my results were as accurate and as precise as I could possibly get them.
I think that any other anomalous results where mostly due to a longer acclimatization or the fact that I did not allow the Hydrogen Peroxide to acclimatize in a different tube, which I would definitely, do if I repeated the experiment.
The evidence that I obtained is sufficient enough to support the conclusions I have come to about the values for the optimum and denaturing temperatures because I conducted my experiment as accurately as I could whit the method I used and did quite a large range and number of repetitions to the results reliable.