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Diluting an Enzyme

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Investigating Whether Diluting an Enzyme Affects the Rate at which it Breaks Down its Substrate Introduction I am doing an experiment to investigate whether diluting an enzyme affects the rate at which it breaks down its substrate. The enzyme I am using is amylase and the substrate is starch. Enzymes are large protein molecules and are essential for the body to function; they speed up reactions and are therefore called biological catalysts. They enable the different products of the reactions to be absorbed and assimilated quickly, without them reactions would take place too slowly for the body to sustain life. Enzymes break down their respective substrate using the lock and key theory; each enzyme has a differently shaped active site, or 'lock', which only one substrate, or 'key,' can combine with. Enzymes are therefore called substrate-specific. Each enzyme breaks down a different substrate. For example, amylase breaks down starch to maltose, pepsin breaks down protein to amino acids and lipase breaks down lipids to fatty acids and glycerol. After an enzyme has broken down its substrate into simpler substances, it remains unchanged. This is very useful because it means that the enzyme can continue this process with a new substrate. Enzymes are also very sensitive to heat. Enzymes have an optimum temperature of 40oC. This means that at 40oC an enzyme works fastest, but above 40oC the active site of the enzyme starts to denature, meaning that it cannot lock onto its substrate so effectively. As the temperature increases above 40oC the active site of the enzyme begins to denature more and more, so less and less of the substrate is broken down, until eventually the enzyme's active site is completely denatured and no substrate can be broken down at all. As the temperature increases up to 40oC the enzyme starts to move around more quickly, meaning that there is more chance of it colliding with its substrate. ...read more.


I mixed 4mls of water with 4mls of starch and left it for forty minutes, testing it with iodine every ten. This was to check that the liquid I was using to dilute the amylase didn't react with starch itself, at least not in the amount of time that I would be leaving the amylase solution and starch together. I found from this that water did not react with starch, because the iodine solution stayed very black. Because the iodine solution did not get at all lighter in colour as I tested the water and starch with it, I can safely assume that it would not break down the starch at all. I tested each strength of solution at least three times, if there was a slightly anomalous result then I tested it four times. By doing this and then calculating an average, I was ensuring that the impact of any anomalous results on my overall results would be minimised. To ensure that this experiment is a fair test, certain steps have been taken. These are; As far as it was possible, each test was conducted under the same temperature; the starch solution was cooled under cold water before it was reacted with the amylase, and we tried to keep the temperature in the laboratory the same. This is very important because temperature affects the rate at which enzymes work; up to 40oC, as the temperature gets higher, enzymes work faster and break down their substrate more quickly. At 40oC the active sites of enzymes start to denature, so the rate at which they work starts to slow down. The same ratio and volume of enzyme to substrate, amylase to starch, was used each time, so they would all be equal. The volume of amylase solution that was mixed up was always the same, 10mls, and the same proportions were used. All the apparatus; dropping tiles, pipettes, beakers, syringes and test tubes, were washed thoroughly before the experiment was begun and after each different ...read more.


Each test was stopped when the iodine turned the same shade of brown, so it was fair. The experiment was repeated three or four times for each strength of amylase solution and an average was calculated, thus minimising the impact of any anomalous results. To improve this experiment I would try to improve the accuracy of it. I would like to have had one complete day to do the whole practical experiment, so that there wouldn't be any difference in temperatures, or in the batches of amylase. I would also improve the accuracy of the measurements. I could have spent more time on the preliminary work and tested all the solutions I was going to use, and have worked out roughly how long each strength solution would take. I could have then, in the real experiment, have left the solutions and the starch for nearly that amount of time, and then tested it every second until all the starch was broken down. This might have given me more accurate results. If I was going to continue this experiment, I would also like to test whether the temperature affects the rate at which amylase breaks down starch. I know that it does, but I would like to find the exact temperature that an enzyme is wholly denatured. I could also test it the other way, by trying to find out at what temperature an enzyme becomes dormant, and stops reacting with the substrate because it is too cold. I would also like to test how far the pH affects the rate at which an enzyme breaks down its substrate, and how far the pH can be from that enzyme's optimum pH, and still enable the enzyme to work. I could also test amylase with starch, after the amylase has been left for different periods of time. I know that amylase does not keep very well, so it would be interesting to see how soon the amylase stops working at its optimum, and whether this could have been a contributing factor to the results of this experiment. ...read more.

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