Tests for Biological Molecules

Starch
1. 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
1. When a reducing sugar is heated with Benedict's solution (alkaline copper sulfate), the solution changes colour from blue to orange-red
  1. 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
1. Boil sample with hydrochloric - this hyrolyses any sucrose present to form fructose and glucose monosaccharides
  1. Cool the solution and neutralise it by adding sodium hydrogencarbonate solution
2. 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
1. 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
1. 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

Resource summary

	Created by Katie Kenney over 9 years ago