Testing for Biological Molecules
- Created by: katelingoody
- Created on: 27-01-17 10:29
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- Testing for Biological molecles
- Lipids
- Identified with Emulsion test.
- Sample is mixed with ethanol, then water is added and the mixture is shaken
- Positive test: Solution turns a milky while /white emulsion forms as a layer on top.
- Negative test: Solution remains clear
- Sample is mixed with ethanol, then water is added and the mixture is shaken
- Identified with Emulsion test.
- Reducing/Non-reducing sugars
- All mono-saccharides and some disaccharides
- Can reduce another molecules/chemical by donating eletrons.
- Test for reducing sugars is Benedict's reagent (Alkaline solution of Copper(ii) Sulphate.)
- 1) Place sample into boiling tube
- If not in liquid form, grind up sample or blend with water.
- 2) Add an equal volume of Benedict's reagent.
- 3) Heat gently in a boiling water bath for 5 mins
- Reducing sugars will react with the Copper ions in the reagent
- Positive test: Blue Cu2+ ions reduced to brick red Cu+ ions
- Brick red precipitate forms
- Negative test: Solution remains blue.
- 1) Place sample into boiling tube
- Note: If sucrose is first boiled with dilute HCl, it will give a positive result
- This is because it has been hydrolysed by the acid to form glucose and fructose (both reducing sugars)
- Non reducing: Boil with HCl and neutralise with Sodium Hydrogen Carbonate
- Qualitative- subjective.
- Can be made Quantitative using a cororimeter
- 2) Calibrate colorimter to 0,using distilled water solution, then measure absorbancy of Benedict's left over.
- 1) Carry out Benedict's test, then remove precipitate by centrifuge.
- Starch
- Iodine test is used
- A few drops of Iodine dissolved in Potassium Iodide solution are mixed with the sample
- Positive test: Solution turns from yellow/brown to purple/black
- Negative test: Solution remains yellow/brown
- Iodine test is used
- Lipids
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