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Investigating the Effect of pH on Enzymes

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Introduction

Investigating the Effect of pH on Enzymes Plan: My aim is to carry out an experiment that will let me deduce the affect that a varying pH will have on the rate at which the enzyme amylase will break down starch into its component parts, which are maltose and dextrins. Background: What is an Enzyme? Enzymes are substances that act as catalysts and so they increase the rate of chemical reactions. In biological systems reactions may occur very slowly or even not at all unless a catalyst is present and this is why enzymes are required. With an enzyme the product of the reaction will occur far faster even to a factor of at least one million. Unlike inorganic chemical catalysts, enzymes are specific. This means that one enzyme normally is used for one reaction. This is as each enzyme has a particular shaped active site, which the substrate (the molecule that is being broken down) will combine with. The shape of the active site depends on the structure of the whole enzyme. The Structure of Enzymes All enzymes are globular proteins, and so have a primary secondary and tertiary structure. The primary structure of a protein is the number, type and sequence of amino acids that make up a polypeptide chain. In the case of the enzyme that we are using (alpha-amylase) the polypeptide chain is around 496 amino acids in length. Each of these amino acids has the general formula NH2.RCH.COOH, where the R group varies giving the 20 different individual amino acids. Two amino acids join together in a condensation reaction, where a molecule of water is removed, forming a dipeptide. The bond that joins them is called a peptide bond; more and more of these are formed forming polypeptide chains. The secondary structure is where these polypeptide chains arrange themselves into another shape, which could either, be into a spiral shape, the alpha helix or into a corrugated sheet structure called a beta pleated sheet. ...read more.

Middle

5 1 in 25 40 x 10-2 18 18 18 9 + 1 1 in 11. 1 1 in 22.2 45 x 10-2 14 14 14 ('-' Indicates that this concentration was not measured as only a certain number were needed to produce an accurate curve) From these results a graph plotting final concentration to average transmission can be produced. This is the calibration curve and it will allow me to read off unknown values of maltose as long as I know the percentage transmission. The calibration curve itself is in the analysis section of this investigation. Main Experiment Method (Implementing): The method used in the main experiment is much the same as that used in the preliminary experiment, as a water bath will be set up using a tri-pod, Bunsen burner and a heat proof mat. The beaker will be the 500cm� volume, so as to fit the 7 boiling tubes for the seven-pH values that are being used. This will be filled with water and left to boil. Once it has begun to boil a 5cm� sample of Benedict's solution will be placed into 7 boiling tubes using a graduated 5cm� pipette and pipette filler. Tin foil will then be placed over the tops of the boiling tubes to stop any of the Benedict's solution evaporating away. They will then be marked with the pHs that are being used (2.2, 4, 6, 7, 8, 9 and 11) with a marker so they can be identified when they are take out of the water bath. These will then be placed in the hot water bath all at the same time so they would boil at the same rate. At the same time 2.5cm� samples of the stock amylase solution made in the preliminary experiment (which had been refrigerated for a short time) will be taken using a 5cm�-graduated pipette as a 1cm� one would mean three measurements so increasing the risk of an error, and this sample placed into 7 different test tubes. ...read more.

Conclusion

To get this you would have to carry out the experiment again and again, possibly using the refinements highlighted above, and although the equipment was there the time this would have taken made it impracticable. This point very clearly shows that one investigation cannot be used alone to prove a set of results and shows that the conclusions and results obtained should be dealt with tentatively. To further my investigation, aside from repeating the same experiment to give more results that would serve to either back up the conclusions found ion this investigation or undermine them, would be to focus in on the optimum value for pH. It was found that pH 7.3 was the optimum temperature, but was only an approximate as the range of values is large. To more accurately find the optimum temperature pH solutions could be made up, such as 6.8, 7, 7.2, etc. The same method used in the main experiment with the changes suggested earlier in this section could be used and the results would produced the same sort of curve but would be much broader and would allow the optimum temperature to be found more accurately. From this smaller range of results you would also be able to deduce more effectively the effect that the change in pH has on genetically engineered amylase, as you will be able to see the effect of changing the optimum pH in small increments and use these results in conjunction with the results obtained in this investigation to see how sensitive amylase is to a change in pH from its optimum pH, i.e. whether small changes in pH do not have much effect shown by the graph further investigation having broad sides or whether small pH changes are significant shown by the graph having steep sides showing greater drop in activity, and with a more accurate optimum pH the conclusions are likely to be more reliable. ...read more.

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