Testing for biological molecules

This contains the three test you need to know for AQA. Benedict's reagent of reducing and non-reducing sugars. The biuret test for proteins. The iodine test for starch

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  • Created by: Vimabi
  • Created on: 02-02-14 13:56

The biuret test

This a test for proteins.
1. Place sample into a test tube, add an equal amount of sodium hydroxide.
2. Add dilute copper (II) sulphate and mix!
3. A purple coloration forms if proteins are present.

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Benedict's reagent

Reducing sugars
1. Add sample to a test tube with an equal amount of Benedict's reagent.
2. Heat the mixture.
3. Turns brick red if sample contains reducing sugars.

Non-reducing sugars
1. Add HCL to sample and boil for 5 minutes.
2. Add sodium hydrogencarbonate to neutralise.
3. Do the Benedict's test

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Iodine test

This is the test for starch.
1. Place 2cm3 of sample into a test tube.
2. Add iodine solution and shake.
3. Solution turns blue/black if starch is present

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