The factors that affect the rate of an enzyme, catalysed reaction
The enzyme we are going to use is amylase. This is the first enzyme that food meets as it enters the body, it is found in the mouth. It breaks down starch, found in most carbohydrates, into glucose, a sugary substance.
This is the main reaction that takes place during chemical digestion. It is necessary as the larger insoluble molecules need to be broken down into smaller soluble molecules. These are then small enough to pass through the small intestine wall into the blood stream and be carried around the body.
Enzymes have 5 important properties:
1. They are always proteins, this is another reason why we have proteins in our diet.
2. They are specific in their action, this means each enzyme is specific to one job.
3. They are biological catalysts, this means that they are not changed in the reaction therefore can be used again.
4. They are destroyed at high temperatures, as they are denatured by heat, most don’t work at a temperature over 45o C, but there are always exceptions, some do work over this temperature.
5. Finally, they are sensitive to pH, most work best in neutral pH but, in the stomach acidic conditions are better and in the small intestine the enzymes work faster in alkaline conditions.
Following on from point 2, the enzymes can only do one job
because they have an active site, this is an area which locks onto the substrate and breaks it down.
This active site can be changed. If the enzyme is exposed to extreme temperatures or pH the active site is damaged and doesn’t fit onto the substrate, therefore not being able to react on it. There are optimum pHs and temperatures for the enzymes to work in.
I am going to investigate how temperature effects the rate of the reaction. Using my background knowledge I predict that the higher the temperature the faster the reaction will happen up to 45 C, as the temperature gets higher than this the enzyme will be denatured and will not be able to react with the substrate. The reaction will get fater because of ideas in the collision theory, it says that the higher the temperature, the particles have more energy, therefore travelling faster and having more chance of colliding and reacting.
I am going to conduct the experiments in as controlled environment as I can. I am going to change the temperature in my experiment and the lowest temperature will be 20 C and the highest will be 70 C.
To make the experiments fair I must make sure I take the samples at the same time for each experiment. I will also use the same volume of each substance each time, I will use 1cm of amylase and 2cm of starch. To get a good set of results I am going to test the substance every 10 seconds. At this time I will use a pipette to take a sample and drop it into iodine solution, while the reaction takes place the solution will turn blue/black and when it has fully reacted it will stay colourless, this is because all the starch has been turned into glucose and the iodine only reacts with starch. I will use a white spotting tile to make it easier to see when the reaction has taken place.
To make my results more accurate and reliable I am going to use personal judgement of one person to determine whether the reaction has taken place.
To keep the experiment safe I will wear safety goggles throughout and be careful not to spill any of either substance.
This is how I carried out the experiments:
1. Collect the necessary apparatus.
2. Prepare a spotting tile with 2 drops of iodine solution in each section.
3. Warm up the amylase and starch separately.
4. When they have reached temperature, mix them together, simultaneously starting the stopwatch.
5. Every 10 seconds take a sample of the solution an put one drop into the iodine on the spotting tile, note down whether the reaction has taken place.
6. Continue until the iodine stays colourless after the amylase/starch solution has been added.
7. Complete this process for each temperature.
8. Clean up apparatus and return to the necessary places.
Graph on next page.
After studying my results I have decided that the results I have gathered do not fit my prediction. In my background knowledge I stated that over 45 C the enzyme is denatured but there are some exceptions, this must be one of the exceptions to the rule.
I have found that the higher the temperature gets the faster the reaction takes place. There is a strong correlation on my graph showing this. This can be explained using the collision theory.
It states that the higher the temperature, the more energy the particles have, this means they move faster, therefore colliding more often making the reaction happening faster.
The way I have conducted this experiment is to the best of my ability and the standard of the equipment I used. As I look back I can think of many floors in the way we carried the experiment out.
1. The water baths were not accurate to the correct temperature so could have affected the result.
2. We had to use our own judgement to decipher the colour of the solution.
3. The intervals between each sample were too far apart to get accurate results.
4. We were only able to carry out the experiment once for each temperature; if we did it 3 or more times it can eliminate anomalous results.
5. In some circumstances the amylase and starch had been mixed accidentally contaminating the sample making the reaction start as they were warmed up. This could make the results unreliable.
If I was to carry out the experiment again I would use a higher standard of equipment and use a different method of carrying out the experiments to give a more accurate and reliable set of results.