How pH Affects the Break Down of Starch by the Enzyme Amylase

How pH Affects the Break Down of Starch by the Enzyme Amylase

Hypothesis:

The optimum pH for the reaction of starch with amylase is pH 7. PH

values lower or higher than this value will result in a slower rate of

reaction. Amylase works in the range pH 3 to pH 11.

Biological Knowledge

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PH changes affect the structure of an enzyme molecule and therefore

affect its ability to bind with its substrate molecules. Changes in pH

affect the ionic bonds and hydrogen bonds that hold the enzyme

together, which naturally affects the rate of reaction of the enzyme

with the substrate. On top if this, the hydrogen ions neutralise the

negative charges of the R groups in the active site so that the

substrate and the active site do not attract and therefore do not

react. The optimum pH for most enzymes is pH7.

In the body, amylase works mainly in the small intestines, where the

acidity from the stomach has been neutralised by the hydrogencarbonate

ions in the pancreatic juices secreted by the pancreas. Therefore, it

follows that if amylase were adapted well to the surroundings which it

is found most commonly at, it would work best in neutral conditions,

which is pH 7. To allow for fluctuations in pH, amylase would need to

work from around pH 3 to pH 11.

Apparatus

Apparatus

Reason/Reference to pilot study

Colorimeter

Values can be obtained measuring the breakdown of starch, instead of

just the colour when the iodine solution is added. If not much starch

is broken down, iodine will colour it blue/black so a low %

Transmission will be obtained. If a large volume of starch broken

down, iodi...

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...ially used

3 cm³ of distilled water with 3 drops of iodine. It then occurred to

me that this was inaccurate, as amylase solution is cloudy. Therefore,

I blanked it with 2 cm³ water, 1 cm³ amylase and 3 drops of iodine.

I decided to experiment with pHs within the range pH 2 to pH7, as I

discovered that pH 4 is the optimum pH, instead of my predicted pH7.

Risk Assessment

· Wear goggles to protect eyes from iodine solution

· If spilt on clothes or skin, wash with water to prevent harm to the

body

· Keep iodine bottle away from edge of table to prevent injury from

broken glassware

Ethical Implications

The amylase solution is taken from an animal. The owner of the animal

must permit this act. The animal's body must be paid respect when the

enzymes are removed so must therefore be treated carefully.