In the very first experiment we chose a different range of temperatures, which turned out to be unsuitable: the temperatures were 20°C, 40°C, 60°C and 80°C. In fact at our first attempt of the experiment our results didn't match our hypothesis, because the increase of the rate of reaction with the increase of temperature, stopped at 40°. This is because of the excess of heat energy, the enzyme had broken down its 3 dimensional shape, becoming denatured. Hence catalyse no longer reacted. It would have been predictable that the enzyme would denature at 40°, since its optimum living and reproducing temperature is 37°C (body temperature). Exposing it to a greater amount of energy produced by a higher temperature would only break its bonds.
Consequently to this discovery, we have decided a more suitable range of temperatures to use: 20°C, 30°C, 40°C and 50°C which are likely to show us a clear pattern of reaction.
Prediction with scientific explanation:
I predict that the breakdown of Hydrogen Peroxide will be quicker when the temperature is increased until it exceeds 40°C. This is because a rise in temperature increases the rate of most chemical reactions and a fall in temperature will slow them down. In many cases, a temperature increase of 10°C will double the rate of reaction in a cell. I am going to investigate the temperature at which this reaction occur. I predict that an increase of temperature will result in an increase in kinetic energy. Since the speed of particles increases, they should collide more often and therefore the speed of reaction increases. The particles will also have more energy thereby speeding up the reaction even more.
In general at low temperatures particles of reacting substances lack energy. An increase in temperature will cause the particles to take in energy, and consequently to move faster and collide more often. More frequent collisions means that more collisions will be successful, resulting in an increase of the rate of reaction.
The same could be said for reactions controlled by enzymes, except that because enzymes are proteins if the temperature exceeds 50°C they will be structurally denatured and ultimately inactivated. This is, indeed, the reason why few cells can tolerate higher temperatures than approximately 45°C.
The mechanism of heat-induced structural denaturation of the enzyme is well understood at a molecular level. The heat breaks the hydrogen bonds between distant parts of the polypeptidic chain of the enzyme, so that the protein loses stability of its three-dimensional conformation. Because such stability is so essential to chemical function, any temperature increase resulting in a structural collapse of the protein will reduce or totally block the enzymatic activity. Therefore I predict that heating the Hydrogen peroxide beyond a certain temperature threshold will gradually kill the experiment reaction.
Fair test:
To make the test fair, the following parameters must remain constant during the course of the experiment: (1) the amount of water in the beaker, (2) the amount of Hydrogen Peroxide and Catalyse, (3) the duration of reaction , and (4) if possible the room temperature. It is very hard to keep the room temperature constant, since the experiment will be run during different days, and it is very likely to have a change of temperature during the intervals of time between one day and another.
If the reaction happens too quickly, I will have to dilute the substrate, to balance out the reaction. I will report accurate results, in order to insure that the test is done fairly.
Experimental results
A result table of the No. of bubbles given off at different temperatures
A graph to show how the rate of reaction varies as a function of temperature
Analysis:
My conclusion matches my prediction. Temperature does, indeed, influence the rate of enzyme activity. More precisely, Hydrogen peroxide breakdown rate is observed to increase as the temperature rises towards the optimum value of 37°C. Above this temperature the breakdown rate is observed to decrease, until a complete stop of the reaction is observed at temperatures beyond 40°C.
From an inspection of the graph, we see that the optimum temperature from the point of view of enzymatic activity is about 37°C, which corresponds to the average body temperature. Probably because it is the enzyme’s optimum temperature, it is also the optimum temperature at which our organism works. It was after 50°C that we started to notice a decrease in the rate of reaction. In the first attempt, at 50°C, the bubbles of oxygen given off went from 19 to 6, and in the second attempt from 17 to 4, which shows a dramatic change of rate of reaction. In some cases a rise of temperature of 10°C will double the rate of reaction. We investigated the temperatures at which reactions occurred. We know that an increase in temperature would result in an increase in kinetic energy. Since I increased the temperature, the particles should collide more, and so the rate of reaction would increase. When we reached 40°C the three-dimensional structure started to break down probably because the collision of particles was becoming harder, due to the continuos increase in kinetic energy, and more often, the reaction couldn’t take place anymore. By the time we reached 50°C, the structure was completely broken, which explains the sudden decrease in the rate of reaction. In the two attempts we carried out the results were very similar, with a difference of one or two bubbles at the most. I can state that my results are trustworthy, since they are very similar, even though the experiments were run at different times during different days. At low temperatures the particles don’t have much energy, that is why the amount of oxygen given off is relatively low. Every enzyme has its own substrate to react with, and different enzymes react differently at different temperatures.
Evaluation:
As I reached the end of my investigation, I have to say my experiment went well, and that I have gained reliable and accurate results to prove my prediction. Although there were some factors which very difficult to keep constant, which might have affected the outcome of the experiment. When measuring the amount of Hydrogen peroxide we might not have measured the exact same amount everytime, due to the deficiency of enough accurate equipment. We might have measured 10.1 ml instead of 10 ml, but this wouldn't have dramatically affected our final results. Another problem was the temperature of the room, which would have been nearly impossible to keep constant through the time in which the experiment was run, since the experiment was carried out over a period of many weeks: the room temperature might have varied, from 18°C to 22°C. This change may have affected the particles in the enzyme, causing the reaction to occur slightly faster than it should. Also when we added the pieces of potato containing catalyse to the substrate, the time I took to put the bung on the tube wasn’t exactly the same in all the attempts, and some oxygen might had given off before I started counting them. For all the other parts of the experiment I have tried to be as fair as possible: the amount of potato put in the tube was cut with the same size instrument all the time, the potato had been conserved in a suitable place for the whole duration of the experiment, so the enzyme inside it would not get denatured. I didn’t gain any anomalous results from the experiment, apart from in the first attempt at it, when the range of temperatures didn’t give a clear enough idea of the pattern the reaction was taking. To improve my method, I could be more precise on the counting of oxygen given off from the reaction. I could use a measuring cylinder to get the amount of oxygen given off in ml, which would be certainly more accurate then me counting the bubbles given off. I could investigate further how the enzyme’s rate of reaction varies with temperatures below 20°C. I already know that at low temperatures enzyme’s have a slow rate of reaction, but my curve would be more complete, and my theory would be clearer. I would have as my minimum temperature 0°C and a range of temperatures that would go up to 50°C in fives, keeping the condition of experiment as constant as possible. I can also repeat my experiment many times in order to measure the variability between experiments. Despite this I consider my results clear enough to prove my beginning prediction.
Bibliography
Some of the material that I have used to back up my prediction was taken from A-level books, which I was given the possibility to borrow in class.
Mc Murry Organic Chemistry, Brooks Cole 1996
