Tests for Biological Molecules

Katie Kenney
Mind Map by Katie Kenney, updated more than 1 year ago
Katie Kenney
Created by Katie Kenney over 6 years ago


AS LEVEL Biology Mind Map on Tests for Biological Molecules, created by Katie Kenney on 01/02/2015.

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Tests for Biological Molecules
  1. Starch
    1. Add a solution of iodine to the sample - if starch is present, the iodine solution changes colour from yellow/brown to blue/black
    2. Reducing Sugars
      1. When a reducing sugar is heated with Benedict's solution (alkaline copper sulfate), the solution changes colour from blue to orange-red
        1. The orange-red is described as a precipitate because the substance comes oit of the solution and forms solid particles dispersed in the solution. This is Benedict's test
      2. Non-reducing Suagrs
        1. Boil sample with hydrochloric - this hyrolyses any sucrose present to form fructose and glucose monosaccharides
          1. Cool the solution and neutralise it by adding sodium hydrogencarbonate solution
          2. Carry out Benedict's test and if sucrose is present in the original sample, the test will give a positive result because glucose and fructose are present
          3. Protein
            1. Add biuret reagent to sample. The sodium hydroxide and copper sulfate will react with the peptide bonds found in protein, which results in a colour change from pale blue to lilac
            2. Lipids
              1. Add ethanol to dissolve any lipid present, then pour the liquid into water contained in another clean test tube. If lipid is present, a cloudy white emulsion will form near the top of the water
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