Zusammenfassung der Ressource
Tests for Biological Molecules
- Starch
- Add a solution of iodine to the sample - if starch is present, the
iodine solution changes colour from yellow/brown to blue/black
- Reducing Sugars
- When a reducing sugar is heated with Benedict's solution (alkaline
copper sulfate), the solution changes colour from blue to orange-red
- 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
- Non-reducing Suagrs
- Boil sample with hydrochloric - this hyrolyses any sucrose
present to form fructose and glucose monosaccharides
- Cool the solution and neutralise it by adding
sodium hydrogencarbonate solution
- 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
- Protein
- 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
- Lipids
- 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