PRACTICAL WORK WITH BIOLOGICAL MOLECULES

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test for STARCH

  • IODINE test for STARCH
  • 
  • test substance may be solid or liquid, place on white tile and add IODINE SOLUTION (yellow orange colour)
  • POSITIVE RESULT = BLUE/BLACK COLOUR
  • NEGATIVE RESULT = NO COLOUR CHANGE - REMAINS YELLOW/ORANGE
  • Iodine bind to centre of AMYLOSE HELIX, changing colour from YELLOW to BLUE/BLACK.
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test for REDUCING SUGARS

  • BENEDICT'S TEST for REDUCING SUGARS
  • 
  • solution placed in test tube, then same amount of BENEDICT"S SOLUTION added
  • HEAT to 80*c in water bath
  • POSITIVE RESULT - COLOUR CHANGE from BLUE to GREEN then YELLOW/ORANGE then RED PRECIPITATE
  • FINAL COLOUR depends on concentration of reducing sugar - LOW = GREEN
  • NEGATIVE RESULT - NO CHANGEREMAINS BLUE

 

  • MOST SUGARS REDUCING SUGARS - NOT SUCROSE
  • when mixed with oxidising agent & heated = redox reaction. Benedict's contains copper sulphate with copper ions, when react ions change to Cu+ to form red precipitate.
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test for PROTEINS

  • BIURET TEST FOR PROTEINS
  • 
  • solution in test tube, add equal amount of BIURET SOLUTION (copper sulFate & sodium hydroxide) & mix
  • POSITIVE RESULT - VIOLET/PURPLE COLOUR
  • NEGATIVE RESULT - NO CHANGE - BLUE OF COPPER SULFATE
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test for LIPIDS

  • ETHANOL EMULSION TEST FOR LIPIDS
  • 
  • crush material in ethanol in test tube, filter into a 2nd test tube with cold water, discard solid residue DONT MIX
  • POSITIVE RESULT -  MILKY EMULSION INDICATES LIPID.
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test for NON REDUCING SUGARS

  • SUCROSE ONLY COMMON NON REDUCING SUGAR
  • if NEGATIVE RESULT WITH BENEDICT'S TEST:
  • add  dilute hydrochloric acid & boil in water bath (acid=catalyst) cool test tube, add alkali then redo BENEDICTS TEST
  • POSITIVE = NON REDUCING SUGARS (PROBS SUCROSE) PRESENT IN ORIGINAL TEST SUBSTANCE, BUT NO REDUCING SUGARS
  • NEGATIVE = NO COLOUR CHANGE - NO NON REDUCING & NO REDUCING SUGARS.
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