Enzymes are proteins, which are made in the cells. Enzymes act as catalysts. Catalysts are chemical substances, which speed up a reaction but do not get used in the reaction therefore not effecting the product merely speeding up it’s production. This means that one enzyme can be used many times. Most chemical reactions involving enzymes are speeded up by a temperature increase. This is also true for an enzyme controlled experiment, but if the temperature goes above 45ºc the enzyme will then start to break down or denature. The names of enzymes normally end in –ASE, this is just like the enzyme were using Catalase. All enzymes are made inside cells, and most of them are left in the cells to speed up reactions in the cytoplasm and nucleus. These cells are called intra-cellular enzymes. There are also extra cellular enzymes, which are let out of the cells and work outside of the cell. Enzymes also like certain working conditions, this includes a certain pH level. If the pH level is not correct for the enzyme it will not work. Enzymes work by binding their substrates (the reactant) to a specially shaped active site. If this active site changes shape then the enzyme will not work. The shape can be changed if the temperature it too high or if the pH around the enzyme is incorrect. Certain enzymes are specific, this simply means that one enzyme acts on one substance but it won’t on another.
Basic Catalase theory –
Enzymes are very large molecules that are synthesized by the cell to do very specific functions. Catalase speeds up the rate of a reaction without being “used up”, or changed. Catalase is an enzyme, which is present in plant and animal cells, and aerobic bacteria. If promotes the conversion of hydrogen peroxide into water and molecular water.
H2O + O2→2H2O+O2
Catalase is located in a cell organelle called peroxisome. In plant cells peroxisomes are involve in the use of oxygen and the production of carbon dioxide, and the breaking apart of N2 to reactive N atoms.
Prediction (based on theory) –
In the range of temperatures that I will be using I predict that at 15ºc the enzyme Catalase will work upon the hydrogen peroxide best therefore producing the most froth. This is because in our human body the temperature is around 37ºc, therefore the Catalase enzyme from a potato is going to be less. The enzymes work best at this temperature however if the temperature increases above 45ºc then the enzyme could start to denature. This means because the enzyme is made up of long chain proteins they will start to unravel. Most enzymes are damaged when they go above 45ºc, due to this fact we have used a range to 50ºc so we can see the effect of going higher that 45ºc.
Procedure (based on theory) –
In this experiment I have got to watch a few factors which if I leave could effect the results. For example I have to carefully monitor the temperature because if it goes too high the Catalase will denature. I will place the test tube with the ratio of 2:1 (Catalase: hydrogen peroxide – to be added later) into the water bath. Once the test tube reaches the correct temperature and doesn’t go above the temperature I will then add the hydrogen peroxide and watch the test tube for two minutes. When I’m doing the 50ºc denomination I’m doing it so I can see what effect the change of shape for the active site does to the results. I will also have to make sure the pH stays at pH 7. Because this also can effect how the Catalase works, and I want the test to be fair therefore the Catalase has to work the same the whole way through the experiment. In my preliminary investigations I found that the best pH for Catalase is 7.
Measurements
Range of values –
For my temperature ranges I will be using the range of 15ºc to 50ºc. I am using these ranges because they are the temperatures, which will produce the best results to prove which temperature, is best. For my pH level I will be using the same level which is pH7. Also like I mentioned earlier the ratio of Catalase to hydrogen peroxide would be 2ml: 1ml, because of my preliminary investigations.
Intervals between readings –
For my temperatures I will be using the range of 15ºc to 50ºc. So the intervals (10ºc) I will be using are 15ºc, 25ºc, 35ºc, 45ºc, 50ºc. Each interval will also be repeated three times. If when doing my experiment I find that it would be useful to do more temperatures I will do so, therefore I can get a better variety of results towards the temperature that seems to be making the Catalase produce the most froth - O2.
Scientific theory –advanced
During the experiment the enzyme Catalase will be acting upon the hydrogen peroxide which is the substrate. For the Catalase to work, the substrate has to touch and “lock” with the Catalase. For this to happen the substrate and the Catalase need to be moving. The collision theory states that the higher the temperature the faster the molecules will move, so this means that if the temperature is high the substrate and the Catalase are more likely to combine because they are more likely to bump into each other. But when the temperature is cool they are less likely to combine because they are moving more slowly.
Lock and Key theory -
The lock and key theory is the joining of a substrate and an enzyme molecule. The molecules start off separate, and combine for a short time, and then separate creating one new substance and leaving the enzyme free to take part in another experiment. For example - Biological catalysts, which are involved, help speed up the breakdown of food, but it is not used up in the reaction. There are different types of catalysts for a different food e.g. Fat. This is because each catalyst if a different shape therefore only certain substrates fit it, so the catalyst and substrate are heated and if they are a match they will collide and fit together.
Diagram of lock and key theory.
The Collision theory -
The collision theory is a “mathematical description of the number of collisions between molecules in a sample of math’s time, useful for predicting rates of reaction.” I found information on the collision theory off of the Internet; I used this because it gives a good understanding as to why the molecules are moving and joining in the lock and key theory. Also included in the collision theory is the idea of the higher the temperature the faster the molecules move therefore the more chance that the substrate and the enzyme combine. Obviously the lower the temperature the slower the enzymes and the substrate move therefore giving a lower chance that they combine.
Secondary sources and Preliminary Work
For my preliminary work I took three different things to do. First was to vary the temperature, secondly to vary the pH, and thirdly to vary the concentration.
Variation of temperature –
When I was varying temperature I used the denominations 15ºc, 30ºc, 80ºc and 100ºc. I kept the pH at 7 and the concentration 2ml of Hydrogen Peroxide and 1ml of Catalase. When I was doing this experiment I found out that the best temperature was 30ºc out of all of the denominations. When I was doing this experiment I found that measuring the temperature was difficult but I found that if I put the test tube into a test tube rack, the test tube was then steady and measuring was easy. I now also realise that I should have used the temperature 37ºc as one of my denominations, to give me a more accurate idea of the best temperature.
Variation of pH –
When I was varying pH I used the denominations pH 2, 6, 7, 8 and 12. I kept the concentration at 2ml of Hydrogen Peroxide and 1ml of Catalase. I also kept the temperature at 30ºc. When I was doing this experiment I found that the best pH was 7. At this pH the Catalase worked at it’s best.
Variation of concentration –
When I was varying concentration I used the ratios: -
I kept the temperature at 30ºc and the pH at 7. When I was doing this experiment I found that the best concentration was 1:2. This was best because there was double the hydrogen peroxide (substrate) in Catalase. I think that there was then enough to act upon the substrate.
Conclusion –
From these three preliminary investigations I found that the best temperature was 30ºc, which is closest to body temperature 37ºc. I also know that the best pH was 7 and that the best concentration was 1:2 (hydrogen peroxide: Catalase).
Get some results –
I used my method and applied my theory to do my experiment, and got some good results. During my experiment I had to change a few things, for example I had to find the optimum time to leave the test tubes after adding the hydrogen peroxide, in my method I didn’t include this, so when I was following the steps I noticed. So I found the optimum time which was 2 minutes, and used a stop clock to time it.
Results table –
Below is how my result table will look.
Results –
When doing my experiment I got my results with a few extra ones; I also got three repeats and worked out the averages. When doing my experiment I added extra temperatures around the point, which gave good results, to help get a better picture of what was happening.
My results –
Results involving skilled use of equipment –
In this paragraph I’m going to write about how I used the equipment. When I was doing my experiment and was using the water baths I made sure the test tubes hooked onto the edge of the water bath and that the thermometer didn’t move inside the test tube affecting the experiment. I think that this kept my results accurate, and didn’t effect the results, which could have happened if I was careless. One thing that could have effected my results is when I was moving from the water bath to the test tube rack. Also the Catalase could have cooled down slightly in this time. I also timed how long I left the Catalase for, which I didn’t plan to do. To do this I used a stop clock to time the two minutes. Also when measuring how much froth had formed from the reaction, I measured it in the test tube rack so that I didn’t move the test tube. If I had of the froth could have mixed with the liquid that was also in the test tube.
In my results I got a couple of temperatures which had the three repeats spread out more than the rest of them. This was 15ºc, which had 14ºc, 13ºc and 12ºc; the other one was 25ºc, which had 6ºc, 6ºc and 8ºc. The reasons above I think contributed to the two misfits.
Even though my results had these ‘misfits’, I think my results are reliable especially as I tried to prevent anything, which could effect the end results. During the experiment I made sure that the concentration stayed the same by carefully measuring out the two substances, and by monitoring the pH level using indicator paper.
Simple Conclusion –
From my result table I know that at 15ºc the Catalase worked it’s best and produced the most froth. I also know that after 45ºc the Catalase breaks down and denatures.
Graph –
Attached.
Trends and patterns –
My graph doesn’t have much of a pattern and I seem to have two misfits. The other results are around the line of best fit though. The results I have go in a negative correlation.
Line Graph
Attached.
Conclusion – Linked to theory –
After doing my experiment I now know which temperature the Catalase acted best upon the hydrogen peroxide and at which temperature the Catalase didn’t work very well. As you can see from my result table the Catalase worked best upon the hydrogen peroxide at 15ºc. My theory said that the higher the temperature the more the enzymes and substrate move around and join, but from my results I know that it was quite a low temperature that the Catalase worked best at. One thing I can prove though is that above 45ºc the Catalase enzymes will start to denature. From my experiment I know that above 45ºc the Catalase enzyme doesn’t act at all upon the substrate.
Prediction review –
In my prediction I said that I thought the best temperature would be around 15ºc, and from my experiment I know that I was correct. I think that when I wrote my prediction I had a much smaller knowledge of my investigation and was lucky to get this correct. But now I am reviewing my prediction I know that I made the correct choice and that the temperature I chose was the best. I chose 15ºc because a potato, which is where the Catalase enzyme comes from, is much cooler than room temperature, which is about 22ºc. I also know from my preliminary investigations and from other references off of the Internet that the temperature that the Catalase would work well on the hydrogen peroxide was 15ºc.
Comments –
I think that it would be quite interesting to investigate lower temperatures around the optimum temperature that I found. For example 0ºc to 14ºc. Also in denominations of 13.5ºc, 14.5ºc and so on. This would then give me a very accurate optimum temperature.
Accuracy -Misfits –
On my graph I have identified two misfits, but there are more results that don’t keep to the line of best fit. The two misfits are at 10ºc and at 25ºc. I think that the 10ºc result should have actually been higher than the 15ºc result. I think this because of the pattern, which is emerging, in my result table. Even though there are two misfits on the graph, on the results table the results make more sense and I think look more useful. On the results table we can see more clearly the areas where the Catalase worked it’s most and it’s least.
Accuracy - Repeats –
Below is a copy of my results table an I have highlighted the repeats which aren’t that accurate.
These results go up in a continuous order, but this mean that there is a gap of 2mm between the 12mm and 14mm results. Even though this is true when we take an average we get a clear average and this is quite reliable. But if I had more time I would have redone these results so I could see if they go any closer.
This result is completely out compared to the two other results. But because there are two other results that are exactly the same we know we can rely on these results. On the other results, which I haven’t mentioned I got quite close, repeats so I know that these are very reliable.
Accuracy - The Graphs –
I think that my results are quite accurate but when I drew my graph I realised a few problems. When I looked at my graph I realised that I really needed to add the result of 40ºc so that the results would line up better even though I didn’t actually take any readings for this result. Even though this wouldn’t have effected the misfits, it would have made my graph easier to read. The accuracy of my graph isn’t that good because of the misfits, but when you look at the table of results they look a lot clearer.
Inaccuracy – Variations in repeats from best-fit line
When I look at my graph I can see that my line of best fit has deviated from some of my points. My line of best fit only hits two points, so I have now added a curvy line of best fit, which seems to fit better. (See graph)
Inaccuracy – Results (perfect)
I think that my results were good but not perfect. I followed my method and added something’s to it, which I had overlooked. I think that this is the kind of experiment that can have so many things, which can vary the results, and make them look a lot more random than they really are. I do think that my results are reliable, and I think that because I have identified the misfits the other results are fairly accurate.
Improvements / Extensions
If I was to re-do my experiment like I mentioned earlier I would change my temperatures and focus more on the lower temperatures rather than the higher like I did. I would also go into temperatures like 15.5ºc, but for this I think I would need to use a computer and LogIt system to measure the decimal temperatures accurately.
Draw diagrams
Check and Spell Check
Graphs
