Enzymes can be denatured at certain conditions. These conditions are high temperatures and extreme levels of pH. The bonds that hold enzymes together are quite weak and so are easily broken by the above conditions. When these bonds are broken the enzyme, along with the active site are deformed, thus deactivating the enzyme. This is known as a denatured enzyme.
The rate of reaction is directly proportional to the enzyme concentration when the substrate is in excess. This is due to the fact that when the enzyme concentration is raised it makes more active sites available to react with a substrate.
At lower temperatures, the rate of reaction rises with a very steep gradient as the temperature increases. This is because the molecules of the enzyme move faster and faster thus causing the rate of enzyme-substrate collisions to increase. We know that the rate of reaction doubles every 10oC. The temperature then rises to such a degree that the enzyme becomes denatured. This is because the molecules of the enzyme vibrate so violently that they break their weak bonds holding the structure of the enzyme together. The perfect temperature for the majority of enzymes is 37oC. For this reason, our body temperature is 37oC.
With a change of pH the weak bonds holding the enzyme together will break. This will denature the enzyme, thus deactivating the active site. A pH significantly higher or lower than 7 will denature the enzymes.
Hypothesis
I predict that the breakdown of starch will be quicker when the temperature is increased until it exceeds 40oC. Then the diastase will no longer catalyse the breakdown of starch. This is because diastase is made up of protein molecules and therefore it is easily denatured by heat, losing it’s shape and no longer able to combine with the starch. I think the rate of breakdown of the starch will increase until this point because the increase in temperature will supply the molecules with more energy to react, and then it will slow down and the rate of reaction will be a lot longer. I predict the final graph will look like the one below, which clearly shows that the results are indirectly proportional to each other. This means that as one of the variables increases, temperature the other one decreases, time. But once the temperature reaches between 45oC to 55oC the time will slow down until eventually the reaction that occurs between the diastase and starch will be too slow to record. I have decided to take three readings for each temperature and then take an average. I believe that this will achieve the best results possible.
Time Taken to Disappear
(Seconds)
Temperature (oC)
Previous Work
Prior to this experiment, a pilot study was carried out. After completing this pilot study I discovered which variables to use and which variables not to use in order to achieve the best results. For the final experiment I chose to use the variable of changing the temperature. I chose to change this because I believe it is the easiest to alter and is almost guaranteed to achieve the best results possible.
Apparatus List
5xWater Baths (35oC, 40oC, 45oC, 50oC, 55oC,)
30xTest Tubes,
2x10ml Syringe,
250ml Beaker for Diastase,
250ml Beaker for Starch,
250ml of 1% Diastase,
250ml of 1% Starch,
Stop Clock,
Safety Glasses,
1xTest Tube Rack,
Marker Pen,
2xThermometer,
1xBottle of Iodine,
Method
The apparatus was collected and labelled as necessary. 5cm3 of Diastase was then put into a test tube marked accordingly. It was marked with a ‘D’ for Diastase and with the temperature of the water bath it was going to be acclimatised in and the experiment carried out in. The same was done for another test tube, but instead of 5cm3 of Diastase, 5cm3 of Starch was put into it. It was labelled the same way but with an ‘S’. Five drops of Iodine solution were then put into the starch test tube, labelled ‘S’. It was shaken until the whole solution went a dark blue colour. A thermometer was then put into both test tubes that were going to be used. The test tubes were then put into the water bath that the test tube was marked with. They were then left to acclimatise until both of the solutions in the test tubes were at the correct temperature. The thermometers that were in the test tubes ensured this. Once they had reached the correct temperature the solutions were mixed and put into one of the test tubes. The stop clock was then started. The test tube was checked every 10-15 seconds. The stop clock was stopped as soon as the entire solution was a clear white. The time was recorded and the experiment repeated another two times for the particular temperature. Once three readings had been taken, an average was made. The temperature was then changed and the whole experiment repeated again.
Evaluation and Analysis of Results
After drawing a line of best fit on my graph, I can quite clearly see that there are one or two anomalous results. These are at the temperatures of 35oC, 40 oC and 45 oC.
Conclusion
My results proved my prediction to be incorrect. My original prediction was that the breakdown of starch is quicker as the temperature increases until the optimum temperature (40oC) after which it begins to slow down. But after drawing my graph it is quite clear that this prediction is incorrect according to the peak temperature that the experiment was carried out at (55oC). This proves that at 55 oC the enzyme is not denatured, otherwise the time taken for the starch to disappear from the solution.
I think my results were sufficient to support a firm conclusion, but if I had the chance to investigate further the effect of temperature on the breakdown of starch I would take more results focusing on the higher temperatures and try to pinpoint the optimum temperature.