biochemical tests

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TESTING FOR REDUCING SUGAR

  • Reducng sugars include all monosaccharides and some disaccharides
  • USE BENEDICTS TEST
  • add benedicts solution to sample and heat (do not boil)
  • if a reducing sugar is present a coloured precipitate is formed
  • colour changes frrom BLUE -> GREEN -> YELLOW -> ORANGE-> BRICK RED
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TESTING FOR NON-REDUCING SUGAR

  • to test non-reducing sugars they must first be broken down into monosaccharides
  • PROCEDURE:
  • boil the sugar e.g. sucrose with dilute hydrochloric acid
  • neutralise the solution with sodium hydrogencarbonate
  • use the BENEDICTS TEST to work out whether it is reducing or non-reducing
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TESTING FOR STARCH

  • USE IODINE TEST
  • add drops of iodine dissolved in potassium iodide solution
  • if starch is present the sample changes from ORANGE/BROWN -> BLUE/BLACK
  • if starch is not present there will be no colour change
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TESTING FOR PROTEINS

  • USE BIURET TEST
  • involves 2 stages:
  •  1... the soultion needs to be alkaline so add drops of sodium hydroxide solution
  •  2... Add some copper(II) sulfate solution
  • if a protein is preset a PURPLE  layer is formed at the surface
  • if there is no protein the solution will remain BLUE
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TESTING FOR LIPIDS

  • USE EMULSION TEST
  • add ETHANOL to substance and shake for 1 minute 
  • pour solution into WATER
  • if lipid is present souliton will turn MILKY
  • no lipid solution will stay clear  
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