2.1.2

Tests for Lipids & Proteins

Test yourself

Emulsion Test

An emulsion is when small droplets of a substance are suspended in another solution. The emulsion test returns a positive result if a sample contains a lipid.

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1) Add sample

  • Place sample in a boiling tube with ethanol.
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2) Shake solution

  • Shake well and leave upright for 2-3 minutes.
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3) Transfer solution

  • Pour the solution into a boiling tube containing distilled water.
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4) Observe results

  • If a lipid is present, a white and milky layer will form.

The Biuret Test

The biuret test is used to test for the presence of a protein in a sample.

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1) Add sample

  • Add sample to distilled water and biuret solution (grind in water if the sample is solid).
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2) Shake solution

  • Shake then leave upright for 5 minutes and observe the colour.
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3) Analyse results

  • The Biuret test changes colour from blue to violet when proteins are present.
    • The result will only be positive if the amino acids are joined together by peptide bonds, as they are in proteins.
    • The result will NOT be positive if the solution contains only free amino acids.

Jump to other topics

1Cell Structure

2Biological Molecules

3Enzymes

4Cell Membranes & Transport

5The Mitotic Cell Cycle

6Nucleic Acids & Protein Synthesis

7Transport in Plants

8Transport in Mammals

9Gas Exchange

10Infectious Diseases

11Immunity

12Energy & Respiration (A2 Only)

13Photosynthesis (A2 Only)

14Homeostasis (A2 Only)

15Control & Coordination (A2 Only)

16Inherited Change (A2 Only)

17Selection & Evolution (A2 Only)

18Classification & Conservation (A2 Only)

19Genetic Technology (A2 Only)

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