What substances contain proteins?

In this investigation, you will determine what types of organisms and materials contain proteins. You will combine different materials with Biuret solution. If a material changes the color of the Biuret solution from blue to purple, that material contains protein.

Materials/Equipment Needed

For each student group:

- test tube rack
- 6 test tubes
- 30 ml Biuret solution
- Samples: kiwifruit, liver, oil, plant leaves, potato, sugar

Some questions to get you thinking about today’s lab:

Which of the samples do you expect to contain protein?

Why do you think so?

What do proteins have that nucleic acids, carbohydrates, and fats don't have that might turn the Biuret solution from blue to purple?

Procedure

1. Label test tubes with the names of the samples and place them in the test tube rack.

2. Place a small amount (the size of your fingernail) of each sample into its test tube.

3. Add 5 ml Biuret solution to each of the test tubes. If the solution is spilled, wash it off with water.

4. Observe the tubes. For which samples does the Biuret solution turn purple? Record your findings in the data table below.

Protein Data Table: Which samples contain protein?

Analysis

1. Based on your results, what types of substances contain protein?

2. What substances do NOT contain protein?

3. Did any samples you didn't expect to contain proteins actually have them?

4. Why do you think it's important to know what substances contain protein?

5. Where do you think proteins come from? How do you think they are made?

6. Draw and label an amino acid. Draw an arrow where the Biuret solution is most likely interacting with the amino acid.

BIOTECH Project Department of Molecular and Cellular Biology The University of Arizona August 3, 1998 Designed by: Ken Kubo, Ph.D. Nadja Anderson, Ph.D. nadja@email.arizona.edu   http://biotech.biology.arizona.edu