Biological Molecules

• Monosaccharides

  Glucose Fructose Galactose
• Disaccharide

  Maltose Sucrose Lactose
• Polysaccharide

  Starch Glycogen Cellulose
• Reducing Sugars are


  all Monosaccharides and Disaccharides except sucrose
• Carbohydrates are made out of

  Carbon Hydrogen Oxygen
• Test for Reducing sugars

  Benedicts test (blue)
• Test for Starch

  Iodine test
• Fats are made out of

  Carbon Hydrogen Oxygen
• When fats are broken down ___ is produced

  3 fatty acids + 1 Glycerol
• Test for Fats

  Ethanol Emulsion Test
• Proteins are made out of

  Carbon Hydrogen Oxygen Nitrogen
• Test for Proteins

  Biuret Test (Blue)
• Function of Carbohydrates

  Source of Energy
• Function of Proteins

  Metabolism, Formation of Muscles, Enzymes, Hormones and Antibodies
• Functions of Fats

  Energy Reserves, Stores fat soluble vitamins
• Protein (Biuret test)


  1. Add 2 cm³ of 10% NaOH to 2 cm³ of the unknown solution

  2. Add 1% copper(II) sulfate solution drop by drop

  3. Shake the mixture after each drop
• Protein (Biuret test)


  • If protein is present in the unknown solution, it will turn a lilac/purple colour
  • If protein is not present, the colour of the solution will remain light blue
• Starch test

  1. Add 2-3 drops of iodine solution to test solution

  2. Blue-black colour indicates presence of starch
• Lipids


  Do not dissolve in water, but do dissolve in ethanol
• Emulsion test for lipids


  1. Shake some of the test (solid) sample with about 4 cm³ of ethanol

  2. Decant the liquid, leaving any undissolved substances behind

  3. Add a few drops of water

  4. If there are lipids dissolved in the ethanol, they will precipitate in the water, forming a cloudy white emulsion. If there are no lipids, the ethanol will remain colourless
• Benedict's reagent


  An aqueous solution of copper(II) sulfate, sodium carbonate and sodium citrate
• Benedict's test steps


  1. Add equal volume of Benedict's reagent to test solution

  2. Shake, and heat for a few minutes (3 min) at 95°C in a water bath

  3. A precipitate indicates reducing sugar
• Colour and density of precipitate

  • Gives an indication of the amount of reducing sugar present, so this test is semi-quantitative
  • Pale blue colour means no reducing sugar
  • Green precipitate means relatively little sugar
  • Orange or red precipitate means progressively more sugar present