See the Movie: The Biuret Test for Peptide Bonds (Proteins)
Add 1 dropper of sample to a tube. Next add 1 full dropper of 10% NaOH and 5 drops of copper sulfate. Swirl the tube and watch for a color change. If the sample contains protein the the color of the contents of the tube will change from light blue to a light or dark purple.
Figure 1. These are the two solutions used in the Biuret Test reagent
Figure 2. The tube on the left contains protein. The tube on the right contains no protein.
Figure 3. Does Solution E contain a protein?
Figure 4. Does Solution B contain a protein?
See the Movie:The Iodine Test for Starch Procedure
Procedure: Add 1 dropper of sample to a tube and 3-4 drops of iodine. Swirl the tube and observe any color change. If the sample contains starch then the contents of the tube will change from yellow to dark blue.
Figure 1. The tube on the left shows a solution that tested positive for starch and the tube on the right shows a solution that tests negative for starch.
Figure 2. Which of these tubes show a positive result for starch?
Figure 3. Does solution A contain starch?
Figure 4. Does solution E contain starch?
See the Movie: The Benedict's Test for Reducing Sugars
Procedure: 1 dropper of sample is placed in a tube and one dropper of Benedict's reagent is added to the sample. The tube is placed in a boiling waterbath for 10 minutes. If the sample contains a reducing sugar (usually monosaccharides and disaccharides) then the contents of the tube will change from blue to red, orange, yellow, or green.
Figure 1. The tube on the left shows a solution that tested negative for reducing sugars and the tube on the right shows a solution that tests positive for reducing sugars.
Figure 2. Does solution D contain reducing sugar?
Figure 3. Does solution E contain reducing sugar?
Figure 4. Which solution contains more reducing sugar, E or D?
See the Movie: The Brown Paper Test for Lipids
Procedure: A small drop of the sample is placed on a piece of brown paper. The paper must sit for 20 minutes under a lamp to allow any water in the sample to dry. If the sample contains lipid then the paper will look like it is still wet.
Figure 1. This shows a positive result for a solution that contains lipids.
Figure 2. The positive control contains an oil drop and the negative control contains a water drop. Solutions A, B, C, D, and E were applied in the bottom left hand corner. Which solutions contain lipid?
Your instructor gives you a sample of half-and- half (a fatty milk product that people put in their coffee). Your instructor tells you to find out what type of organic macromolecules are in the sample.
Figure 1. The half-and-half sample given to you by your professor.
Question 1: Which organic macromolecules do you hypothesize to be in the half-and-half?
Question 2: Which tests should you do to test for each of these molecules and how do you do them?
Click here to go to the results page to test your hypothesis.
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Written by Michelle Furlong and pictures by Christopher Kodani and Barbara Foster. Clayton State University Morrow, GA Copyright 2002 – Department of Natural Sciences, Clayton State University. Do not copy or use anything from these pages without written permission.