MACROMOLECULE LAB: Testing for the Presence of Macromolecules
Introduction:
There are four broad classes of macromolecules that can be found in living systems. Each type of macromolecule has a characteristic structure and function in living organisms. You can use your knowledge of the basic structure of each macromolecule to perform tests in the lab that detect the presence or absence of key functional groups or overall characteristics in various substances. In this lab, you will utilize the following procedures to detect three of these macromolecules in everyday household items -- note what each procedure will detect in which macromolecules.
Tests:
Chemicals are used many times as indicators -- that is, they show us if the presence of specific macromolecules can be found in given substances. This lab focuses on identifying three of the four macromolecules we have studied (carbs, lipids, proteins) using INDICATORS. Read the procedures for the Macromolecule Lab and complete the indicator table below.
INDICATORS are chemicals that react or change color in the presence of another compound. We use them to test for the presence (or absence!) of specific compounds.
Table 1. A list of the indicators (detection reagents) used to reveal the presence of specific macromolecules.
Test (Procedure) Structure/Molecule Detected: Structure/Molecule Found in:
Benedict's Reducing Sugars (sugars with a free aldehyde or ketone group; typically, monosaccharides) Carbohydrates
Iodine Starch Carbohydrates
Lipid Stain Water insoluble substances Lipids
Biuret's Peptide Bonds Protein
Table 2. Chemical explanations for the colorimetric changes observed in macromolecule detection tests.
Detection Reagent Explanation of Detection
Benedict's Contains Copper Sulfate. Copper binds to oxygen in the free aldehyde or ketone group and the Copper Oxide that is formed transmits a brown color
Iodine Iodine interacts with and binds to a structure in the starch molecule, the new structure transmits a dark bluish black color
Lipid Stain Water insoluble substances interact with other water insoluble substances. Does it dissolve in water?
Biuret's Contains Copper Sulfate and Sodium Hydroxide. Copper Sulfate actively binds to the peptide bonds found in proteins, and the structure formed transmits a violet color in an alkaline (basic) environment, which is provided by the presence of the NaOH.
Procedure:
Although these procedures may not be identical to your Lab, they provide similar methods
LIPIDS (1 test)
TEST 1: Testing for Lipids
1. Tear off a piece of paper towel 30 cm long and put the names of your group members in the upper right-hand corner.
2. Draw 6 small squares, approximately 3 cm each, and label each with the name of 1 of the foods (water, oil, milk, oatmeal, apple juice, and Unknown X).
3. Put 1 drop of each of the foods in the corresponding boxes on the paper towel.
4. Put the paper towel aside while you do the other 4 tests.
5. When the paper towel is dry, record your observations in the data table below. Look for a grease stain.
CARBOHYDRATES (2 tests)
TEST 2: Testing for Starches
1. Fill 6 wells in your well plate: water, oil, milk, oatmeal, apple juice, and Unknown X. (see diagram)
2. Add 10 drops of Iodine Solution to each well.
3. Check for any color change and record data in table.
4. Clean and dry well plate
TEST 3: Testing for Sugars
1. Put 1 dropper full of each food (water, oil, milk, oatmeal, apple juice, and Unknown X) in 6 different test tubes. Make sure to LABEL all test tubes.
2. Add 10 drops of Benedict's Solution to each test tube and place them all CAREFULLY into the hot water bath for 3-5 minutes.
3. Remove test tubes from hot water bath using designated tongs and place them into test tube holders. Note the color change and record into the table.
4. Wash all test tubes and place in test tube racks upside-down to dry.
PROTEINS (1 test)
TEST 4: Testing for Proteins
1. Fill 6 wells in your well plate: water, oil, milk, oatmeal, apple juice, and Unknown X. (see diagram)
2. Add 10 drops of Biuret's Solution to each well.
3. Check for any color change and record data in table.
4. Clean and dry well plate
Question 1
Which macromolecules (or types of macromolecules) did you test for in the Labster simulation? What tests did you use for these macromolecules (be specific)?
Question 2
How do you know from the test that lipid macromolecules were present in the food tested? protein macromolecules? carbohydrate macromolecules?
Question 3
What controls did you use to ensure the results from each test was correct? Be specific for each macromolecule.
Question 4
Which three samples tested in the Labster simulation contained three different macromolecules? Which sample only had one macromolecule? What was your suggestion to Alice to help her eat a more nutritious salad?