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Investigate how the enzyme amylase is affected by different pHs.

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Investigation of the effects of pH on amylase Aim: The target of this experiment is to investigate how the enzyme amylase is affected by different pHs. Prediction: For my experiment, I'm using salivary amylase so I predict that the rate of reaction will be highest at pHs from 7 to 8. Reason for prediction: Enzymes are proteins, they are long strands of amino acids that are held into a 3D shape by weak bonds. The pH affects the charge of the amino acids at the active site, so the properties of the active site change and the substrate can no longer bind. Amylase is found in the mouth and small intestine, where the conditions are neutral to slightly alkaline. Method: I used buffers to vary the pH of the different solutions. Iodine was used to test for the presence of starch. I used a colorimeter with a red filter to measure light intensity and therefore the amount of starch present, iodine solution is naturally a red/ orange sort of colour so the red filter will allow red light past to compensate for this. Iodine with distilled water is set to 100% light transmission. ...read more.


Amylase is an enzyme, therefore it is a protein, and like all proteins, it consists of long strands of amino-acids, in an enzyme, these are made into a 3D shape by weak intermolecular bonds. The active site of an enzyme is specific to certain substrates and the enzyme is specific to certain pHs. The way pH can reduce the rate of reaction is by changing the charge around the active site. Acids contain H+ ions, they are strong oxidizing agents whilst alkalis contain OH- ions, they are reducing agents. This can affect the ionic bonds that are holding the enzyme in shape and may also affect the R groups in the active site which form temporary bonds with the substrate. There will be a pH, special to each enzyme, at which the net charge on the molecule is zero. This is called the isoelectric point (pI). The charge and charge distribution on the substrate and product will also be affected by pH changes in a similar manner to the effect on enzymes. Increasing hydrogen ion concentration will, additionally, increase the successful competition of hydrogen ions for any metal cationic binding sites on the enzyme, reducing the bound metal cation concentration. ...read more.


The meter should read either 100% light transmission or zero optical density. ? Empty out test-tube and wash well. ? Place 5ml of concentrated starch and 2ml of amylase into a water bath at 37 degrees Celsius and leave for 10 minutes. ? Add 2ml of buffer, the starch and then 3 drops of iodine to the test tube. (Test buffer for pH before hand) ? Mix well and add the enzyme, mix well and take the reading on the colorimeter after 3 minutes. ? Repeat this with all the other buffers. ? Remember to wash test tube thoroughly in-between each experiment. I think that my results were quite accurate; I was able to get clear, unambiguous readings from the colorimeter. It is also reliable because I had repeated the tests five times and I have gotten quite similar results. I did get one anomalous result, but then I realised it was because the buffer had been contaminated, I tested it with universal indicator solution and found that instead of being pH 7, it was slightly acidic. In any future experiments, I would also use a wider range of pHs to get a more accurate and reliable graph. However, in this experiment, the buffers were unavailable at the time so I could not use them. WenXi Chen ...read more.

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