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Starch and diastase with respect to pH

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Starch and diastase with respect to pH Aim The aim of this experiment is to assess the effect of pH on enzyme activity. To do this I will use diastase as the enzyme and starch as the substrate, I will then vary the pH and measure the effects. Hypothesis There will be an optimum pH, between pH 4 and pH5, at which diastase will hydrolyse starch. Background information Enzymes are globular protein molecules that are biological catalysts, so they reduce the energy needed for the reaction but don't get used up themselves. Being a globular protein, enzymes are formed from a tertiary structure, so they are 3-D molecules. As a result they are able to have an active site, this is where the substrate binds to the enzyme and is broken down into the products. An active site consists of 3-12 amino acids and it is thought that the active sites have specific shapes that correspond to specific substrates. Consequently the enzyme can only break down that particular substrate molecule, this is known as the lock and key theory. However recent research has shown that the enzymes active site is not the right shape to start with, but once it combines with the substrate molecule a small change occurs in the shape of the active site. Subsequently the substrate fits better in the active site, this is known as the induced fit hypothesis. An enzyme can be affected by different factors. They can be denatured by high temperatures because the particles within the enzymes receive energy as the temperature rises, so a large rise in temperatures results in the molecules vibrating a lot. This disrupts the weak hydrogen bonds holding these particles together the ionic bonds are also broken and so the enzymes active site collapses, this means that the enzyme can no longer break down the substrates as the substrate won't fit in the active site anymore consequently the rate of reaction is decreased. ...read more.


* Substrate concentration - we will make sure that we use the same amount of starch each time and use the same measuring cylinder * Enzyme concentration - we will make sure we use the same amount of diastase for each experiment and we will use the same syringe * Time - we will begin timing as soon as all the diastase has gone into the cuvette and as soon as the 4 minutes is up we will add the iodine and put it straight into the colorimeter. * Apparatus - we will use the same apparatus for each thing, e.g. we will use the same syringe for pH and a different one for diastase. Also when changing pH, the syringe will be washed out. * Once every thing is in the cuvette we will give a quick shake and then leave it in a test tube holder. Preliminary We conducted a preliminary following the method above, but not using any pH buffers so it was a control. We also conducted another where we added the iodine from the beginning and put it straight into the colorimeter, and at the end of each minute for 4 minutes we recorded the results. Preliminary results Experiment Transmission (%) Control 72% pH 1 minute 2 minutes 3 minutes 4 minutes 4 33% transmission 40% transmission 42% transmission 41% transmission We can establish from these results that the control worked well. However when we took the test tube out of the colorimeter on the second experiment we noticed that the iodine hadn't mixed well with the other solutions so we decided to keep the method the same. Results Temperature = 20�C Red = anomalies Transmission at different pHs Experiment no. pH 4 pH 5 pH 6 pH 7 pH 8 pH 9 1 80% 93% 93% 90% 90% 78% 2 82% 90% 90% 92% 75% 52% 3 83% 82% 94% 87% 84% 46% 4 80% 94% 93% 79% 40% 5 82% 89% 78% 6 89% 92% 7 89% Average (excluding anomalies) ...read more.


Also when we first added the iodine it went black but it soon began to clear and by the time we had taken the reading it was very clear. However we couldn't keep the solution in the colorimeter and then add the iodine straight after the four minutes, as the light that needed to pass through the solution was quite near the bottom and you needed to swirl the solution after adding the iodine so it would mix. To get better results we would need more time to get more results so they become concordant and we would be able to get a better understanding of what was happening when you varied the pH. If it were possible, some sort of solution that could stop the reaction would be useful so that when we added the iodine the reaction wouldn't keep on going. Also I would imagine that by using smaller amounts of each solution would mean that we would be able to add the iodine to the cuvette when it was in the colorimeter as the solution would need to be mixed, so we would get more accurate results. In addition, if we added more iodine we would be able to ensure more of it was mixing and quicker. Additionally we could use new syringes every time we changed pH buffer solution, this would ensure accuracy. Furthermore we could begin timing as soon as the measuring cylinder is overturned, so that by the time the solution has mixed, the timer would have started. Generally we would have to be extremely careful when using the colorimeter, to ensure the table wasn't knocked. We would also have to place the cuvette in the colorimeter very carefully. Despite the fact that there were many opportunities for the results to become unreliable and inaccurate, the results that the experiment did yield followed a general trend and followed what was expected when the pH of the solution was altered. ...read more.

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