biochemical tests for molecules

• Benedict's test is for sugars

  • sugars can be classified as reducing or non-reducing
• reducing sugars

  • add Benedict's reagent (blue) to a sample and heat it in a water bath orange -red precipitate indicates a reducing sugar is present
  • the higher the [] of reducing sugars the further the colour change will go
• non -reducing sugars

  • eg sucrose
  • test a sample to check if there are reducing sugars in there in the first place
  • take a separate sample and boil it with HCl to hydrolyse the sucrose into glucose and fructose
  • cool the solution and use sodium hydrogen carbonate solution to neutralise it
  • test for reducing sugars again
• testing for carbohydrates

  • iodine test for starch, is present turn from yellow to blue/black
• testing for proteins

  • Biuret test, if proteins are present , solution will turn from blue to lilac
• testing for lipids

  • emulsion test, take a sample and mix thoroughly with ethanol
  • pour the solution into water in a clean test tube
  • a cloudy white emulsion will form in the presence of lipids
• colorimetry is used to determine the [] of glucose solution

  • use Benedict's reagent and a colorimetry to get a quantitative estimate of how much glucose there is in a solution
  • is a device measure the strength of a coloured solution, seeing how much light passes through
  • measure the absorbance, the more [] the colour the higher the absorbance
• use of biosensors

  • device that use biological molecules such as an enzyme
  • biological molecule produces a signal and produces and electrical signal by a transducer
  • can determine the [] of glucose in a solution and can even detect contaminants in water
• use of chromatography

  • separate mixture into its constituents
  • mobile phase = where the molecules can move, is the liquid solvent
  • stationary phase = molecules can't move the chromatography paper
• how to calculate the Rf value

  Rf = distance travelled by the spot/ distance travelled by the solvent
• sometimes with colourless molecules you can't see where they finish:

  • UV light
  • ninhydrin = amino acids
  • iodine