An enzyme molecule is globular and very large but only a small part of it, the active site, is involved in the reaction. The substrate molecule fits into the active site and is held there until the reaction is complete. The product is then released and the enzyme is once again ready to take part in the reaction. This is known as the lock and key hypothesis. The active site has a distinct shape, rather like a lock. Just as only the right 'key' will fit a lock, so only the right substrate has the right shape to fit into the active site.
Prediction:
I think that as the temperature increases, the enzymes will gain kinetic energy and be able to break down the substrate much faster until a certain which will be around the 37 Celsius (which is body temperature). Then the graph (as in the introduction) will go down again because the enzymes will become denatured and the substrate will no longer fit the active site, all the sites will be deformed. I predict that the breakdown of starch will be quicker when the temperature is increased until it exceeds 40° C. Then the amylase will no longer catalyse the breakdown of starch. This is because amylase 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.
Preliminary Work:
The purpose of the preliminary work is to make sure that the actual experiment goes well and our results are accurate.
The concentration of the enzyme amylase has to be changed to fit the experiment. If it is too concentrated the starch will be digested too quickly and to time the reaction with a stopwatch will be impossible – and any timings made will be very inaccurate because of the slow human reaction time. But then again, if the enzyme concentration is too low then the reaction will take far too much time, and not a practical experiment to do in a short period of time. For the experiment we will be doing, the enzyme concentration will be 1%, this will make the reaction not too fast and not too slow either.
Room temperature is also an issue here. The optimum (the point at which it is at its best) temperature of amylase is around 37 Celsius e.g. body temperature. So for the preliminary experiment taking place we will use the temperatures: 20, 30, 40, 50, and 60 degrees…the reaction time will be taken down. This will help us to see whether our real experiment temperatures will be of interest and use.
Method:
Equipment List
For this experiment you will need:
- 5 Test Tubes
- Test Tube Rack
- Amylase (enzyme)
- Starch
- 2 x 10 cm3 measuring cylinder
- Water Bath
- Thermometer
- Stopwatch
- Iodine
- Pipette
By means of a measuring cylinder, measure 2 cm3 of starch and transfer it into a test tube. Do the same with amylase, but into a different test tube. Put the test tubes into the water bath (at various temperatures). Place a thermometer into the starch solution and then put 2 drops of iodine into the starch. Once the temperature becomes constant record the temperature on the thermometer then mix the amylase with the starch and begin the timing with the stopwatch. Note down the period time it takes for the solution to transform to a clear substance. Then do this again but at a series of different temperatures. Repeat each temperature twice and find the average to get more exact results.
Dependant variable: rate of breakdown of starch, time
Independent variable: temperature of solution
Control variable: volume of starch solution
volume of amylase solution
concentration of amylase solution
concentration of starch solution
Fair Test :
To make this experiment fair, a few factors have to be taken into consideration. The same amount of starch and also amylase must be used so that the length of time that it takes for the starch to be digested is accurate. The temperature must remain steady while the substances are reacting and the concentration of the enzyme must stay the same so the experiments results are precise. Different measuring cylinders should also be used for the starch and the amylase so that they do not react inside.
Results :
Temperature (°C) 20 25 30 35 40 45 50
Time (secs) 1st 150.40 113.50 22.80 18.00 14.60 11.40 7.90
2nd 144.60 106.10 20.20 17.80 12.00 9.30 8.50
Average 147.50 109.80 21.50 17.90 13.30 10.40 8.20
Rate of reaction 0.0068 0.0091 0.0465 0.0559 0.0752 0.0962 0.1220
Analysis :
The Effect of Temperature:
Optimum Temperature
Rate of
Reaction
0 10 20 30 40 50 60 70 80 90 100
Temperature /ºC
At the lower temperatures, the rate of reaction rises with a very steep gradient as the temperature increases (0-36ºC). 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 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.
As shown in the graph, the perfect temperature for the majority of enzymes is 37°C. For this reason, our body temperature is 37ºC
Evaluation :
I think this experiment was quite accurate in finding an answer to our aim. On the other hand many aspects of what was carried out may be improved e.g. the reaction time of a human.
The main problem with this experiment was that you could not tell the exact time that the starch had been digested by the amylase enzyme. It was very hard to tell when the liquid had gone wholly clear – when there is no longer starch present.
Also there is a persons reaction time, which makes the test not as accurate as it could be. It takes around 0.2 seconds to react to the change in temperature and this makes the timing on the stopwatch imprecise. This should be taken into consideration.
