The “lock and key” theory states that each enzyme has its own formation (pattern) to fit certain chemicals. Each enzyme has what is known as an active site, this is where certain chemicals can fit exactly into the enzyme, like a jigsaw. While the chemical is in the active site a chemical process takes place, where changes to the chemical are made, a new product is then released. In this case the starch fits exactly into the enzyme called amylase, when it is in the active site the starch is broken down into simpler sugars (glucose), once this has taken place the simpler sugars are released, and the process happens again, until all of the starch molecules have been broken down. If there is a higher concentration of starch present then the amylase will simply work at a faster rate, however there is only a certain speed in which they can work.
Therefore if the concentration of starch is too high, it will take longer for the enzymes to break it down, as there are only a certain amount of enzymes that are present. If they are all being used then other starch molecules have to wait before they can fit into an active site. This leads to the experiment time increasing, as the amylase can only break down certain amounts of starch per second.
Variable Table
Plan
I will be preparing an experiment, to see how long it takes for the enzyme amylase to break down starch into simpler sugars. I will use 1cm3 of amylase and 10cm3 of starch solution. I will mix the two together and test the solution at intervals of 30 seconds.
The equipment I will be using is as follow: 5 test tubes, a test tube rack, a pipette, a small beaker, dimple tiles, stop clock, and an iodine indicator.
I will mix 1cm3 of amylase with 10cm3 of starch at the concentration I am using; I will then automatically start the stop clock. After 30 seconds I will place the pipette into the test tube and take a sample of the solution. I will test the solution in an Iodine indicator, which will be in dimple tiles, to see if the starch has been broken down, I will carry on testing the solution until all of the starch has been broken down by the amylase. I will be able to test this, as if starch is present then the Iodine will turn black, all starch has been broken into glucose when the Iodine remains orange.
I will be varying the concentration of starch with a range of, 1%, 2%, 3%, 4% and 5%. This range will enable me to discover at which concentration the enzyme can no longer work at a faster speed, therefore remaining constant, which will increase the experiment time. In theory the 5% solution should take five times as long as the 1% concentration.
To change the concentration of the starch, I will simply use the 5% concentration and dilute it with water for the necessary concentration, e.g. 2% will need, 4cm3 of starch and 6cm3 of water.
Results table
The first results table will show at what time the starch began to break down and then the final time in which the experiment took. This will be done for all concentrations, and all three experiments, which were carried out.
Key
B = black
DB = dark brown
O = orange
The next results table will show at what moment the starch was fully broken down in each experiment, along with the average time from all three experiments taken.
These results, are not completely accurate as we tested the solution at 10 second intervals therefore we could only say that the starch had been broken down, in between 10 second intervals, e.g. between 50 and 60 seconds.
Conclusion
I have discovered that as you increase the concentration of the substrate, the time it takes the enzyme to break it down also increases. This ties in with my prediction, and my “lock and key” theory, stating that there are only a certain amount of active sites, therefore only a certain amount of starch molecules, can follow out the process at one given time. I have noticed that the time difference between the 4% and 5% concentration, is lower than the differences between the other concentrations. This may be because, my earlier theory, which was that as the substrate reaches a certain concentration it will have little or no more affect, this is due to the enzyme becoming saturated. The reaction rate will remain at a steady speed, from that moment on.
However with the 4% experiment, one out of the three that we carried out, took a lot longer than the other two did, this suggests that something was wrong with that particular experiment, to get an anomalous result such as that.
Another point, which I have discovered, is that the difference in time from the 1, 2 and 3% solutions has almost doubled. This suggests what I earlier predicted, that as you double the concentration the time also doubles; as I stated the 5% should in theory take 5 times as long as the 1% solution. As I mentioned, this near enough worked up until 4%, where the time difference decreased.
Although most of the experiments varied in time slightly, there was only one anomalous result, that being experiment 1 on the 4% solution. This shows that my results are scientifically correct. As science states that as the substrate concentration increases then the enzyme will take longer to break it down into simpler sugars.
Although to begin with adding a higher concentration will cause the amylase to work at a faster rate, it is physically impossible for them to work at the same rate throughout the experiment, as there simply becomes to many starch molecules to break down, in a certain time.
This conclusion firmly supports my prediction, as I stated that the time would increase proportionally to the concentration, however the reaction rate will continue at a steady speed, after reaching a certain concentration. This is near enough what happened, with the time almost doubling to begin with, but then closing in towards the end.
Evaluation
I think that the experiments went really well, with all but one result proving to be correct, and agreeing completely with the science related to the investigation.
Although we could not get an exact measurement of the time, to the last second, it was very close, and as accurate as we could make it. Our results were in-between 10 seconds, e.g. between 60-70 seconds. However it was impossible to be able to test the solution every second, so these results were the closest we could get to the truth.
To begin with we were only going to test the solution every 30 seconds as it says in the plan, however we soon realised that this was too much of a gap, as the colour of the iodine was changing to quickly.
Some results may have been affected by the room temperature, as the experiments were carried out over a number of days, therefore room temperature had changed, and could have slightly affected the results. If I were to carry out the experiment again, I would measure the temperature of the room, and try to get it near enough the same every time we did an experiment. Therefore ensuring that this would not be an issue.
There is enough substantial evidence, to support the conclusion, and to use as being scientifically proven. By doing each experiment three times, we ensured that our results were substantial, and were able to notice if something had gone wrong, to be able to eliminate that result, from the conclusion.
