o Lab tests to identify biomolecules:Biochemhelp

Laboratory tests for Biomolecules


There are specific tests to identify single sugars,starches,proteins and lipids.
identify biomolecules

1.Test for monosaccharides (glucose,fructose etc)
Prepare a hot water bath with tap water at 80 Celsius .
Put 3 ml of your samples of sugars such as fructose,glucose,starch, and any unknown solution into separate test tubes Put the samples(test tubes) in the water bath at 80 Celsius.Observe for 6 min and record any color change. Refer to the following table to find approximate sugar concentration.
Color of Benedict's reagent Approximate sugar concentration
Blue nil
Light green 0.5-1.0%
Green to yellow 1.0%-1.5%
Orange 1.5%-2.0%
Red to red brown >2.0%
2.Starch Test: Lugol's solution contains iodine and is an indicator for starch.Iodine turns blue-black in presence of starch.
Method:Using a medicine dropper,place a drop of unknown solution on a depression spot plate and add a drop Lugol's solution. Colour change to blue-black indicates presence of starch.

3.Sudan IV lipid test:

Sudan IV is an indicator of lipids. Lipids turn from pink to a red colour.
Method: Take 3 ml of unknown sample in a test tube and add 6 drops of Sudan IV indicator. Put a stopper on testtube and shake vigorously for 2 min. Formation of a red ring at the top of the solution indicates the presence of fat.
Alternatively a translucent lipid test can be used to test for fats. Draw one circle(10 cm diameter) on a piece of unglazed brown paper.Place 1 drop of water in the circle and label the circle accordingly.When the water has evaporated hold both papers to the light and observe.

4. Protein test:
Biuret reagent reacts with the peptide bonds that join amino acids together, producing colour changes from blue to pink(+),violet(++),and purple(+++).The + sign indicates the relative amounts of peptide bonds.

Method: Measure 2 ml of unknown solution and add 2 ml of Biuret reagent .Tap the test tubes with your fingers to mis the contents.Record the colour changes.