Identifying Macromolecules Lab
Purpose
To test for the presence of macromolecules in various materials.
Background
The most common macromolecules (organic compounds) found in living organisms are lipids,
carbohydrates, proteins, and nucleic acids. Common foods, which often consist of plant materials or
substances derived from animals, are also combinations of these macromolecules. Some of these
compounds can be detected by taste, while others cannot. Therefore, scientists use certain tests to
identify the presence of macromolecules. Often these tests utilize colorimetry (color changes) to
indicate positive results.
Positive tests for…
Simple Carbs – Benedict’s reagent will turn a variety of colors based on concentration
(Burgundy – High, Orange – Moderate, Yellow/Green – Low; Remains Blue - Negative)
Complex Carbs – Iodine solution will turn blue-black (remains yellow/brown if negative)
Lipids – Sudan III stain will dissolve in lipids, turning them red
Proteins – Biuret reagent will turn pink to violet (remains blue if negative)
Introduction
You’re a scientist at the Food and Drug Administration’s Center for Nutrient Analysis in Atlanta, Georgia.
You analyze food based on the label declaration. Tests are performed for proteins, lipids and
carbohydrates. Recently, there has been fear of an attack by a new species of undead (similar to a
zombie). Scientists believe the only way to combat this attack is by feeding them a substance with high
levels of complex carbohydrates and protein, since these macromolecules appear to kill the new
species’ since their cells can’t break down the molecules. Scientists have also found that the undead
seem to thrive and grow rapidly when fed simple sugars. Interestingly, lipids seem to have little effect.
Your team is taking a break from the regular task of food label analysis in order to determine which of
three substances – yogurt, milk or oatmeal – will be the best food to fight off the invasion, based on the
tests you will be performing today. It is up to you and your team to save Earth!
Materials
Test Tubes & Rack
Hot Plate
Beakers
Pipettes
Distilled Water
Cooking Oil
Glucose Solution
Sucrose Solution
Starch Solution
Apple Juice
Potato Solution
Egg Whites
Buiret Reagent
Benedict’s Solution
Sudan III Stain
Iodine
Yogurt
Milk
Oatmeal Solution
Procedure (GOGGLES MUST BE WORN FOR THE ENTIRE LAB PERIOD!)
Lipid Test
1. Obtain eight test tubes and label each with the name of a different solution
2. Fill each test tube approximately one-quarter full with the correct solution
3. Add 10-15 drops of Sudan III stain to each test tube
4. Gently shake the contents of each test tube
CAUTION: Use extreme care when handling Sudan III to avoid staining hands or clothing
5. Record a “+” if lipids are present or a “-“ if lipids are not present (you may include color info, too)
This is sometimes a difficult test to determine positive or negative…ask for help if needed
6. Wash test tubes thoroughly (if continuing to other tests, labels may remain)
