Identifying Macromolecules – An Investigation
Adapted from Macromolecules Inquiry: Transformation of a Standard Biochemistry Lab by Elizabeth Unsworth
(http://www.yorkprepsc.org/www/ud00/8/891e0e467c0749b095bfd9c05b7e680b/Personal_Documents/Unsworth%20Article.pdf) and Identifying Macromolecules
by Uncredited (http://www.nesscityschools.org/vimages/shared/vnews/stories/53f3996a455d1/Macromolecules%20Lab.pdf)
SC.912.L.18.1 - Describe the basic molecular structures and primary functions of the four major categories of biological
macromolecules.
The four macromolecules that make up most biological systems are carbohydrates, lipids, proteins, and nucleic acids.
The prefix macro- means large, so these “large molecules” are found throughout living things. For instance, the cell wall
that surrounds a plant cell is made of the carbohydrate starch; the cell membrane that surrounds all living cells is
composed of a specific type of lipid, called a phospholipid; muscles in the bodies of animals are composed of proteins;
and nucleic acids can be found in the nucleus of plant and animal cells. As you can see, even though these are “large
molecules” they are small in relation to what we can see with the human eye. In this aligned investigation, you are
going to test for the presence of different macromolecules in foods that may be consumed in an average daily diet. You
will also have to identify both the structure and the function of these macromolecules after observing the outcome of
each test.
Indicators (change color when exposed to specific compounds) –
Biuret’s Reagent – changes color from blue to violet in the presence of protein.
Biuret’s contains NaOH, sodium hydroxide, which is a strong base. Do not allow contact with your skin or other
material.
Benedict’s Solution – changes color from blue to green in the presence of a small amount of simple sugars, from blue to
orange in the presence of a moderate amount of simple sugars, and blue to brown in the presence of a large amount of
simple sugars.
Benedict’s Solution can stain clothing. It also only changes color after being heated for 3 to 5 minutes in boiling
water. Extreme caution should be used when dealing with warming tubes.
Iodine – changes color from brown to dark purple in the presence of starch.
Iodine is poisonous and can stain hands and clothing. Utilize appropriate lab safety practices when dealing with
iodine and ask your teacher for assistance if you have any questions.
Sudan III – changes the color of the sample red and you can look closely and see individual lipid molecules.
Sudan III can stain hands and clothing. Utilize appropriate lab safety practices when dealing with Sudan III and ask
your teacher for assistance if you have any questions.
Pre-lab questions:
What is the purpose of having distilled water as one of your test substances?
__________________________________________________________________________________________________
__________________________________________________________________________________________________
What macromolecule will we not be testing for in today’s lab? What is the function of that macromolecule?
__________________________________________________________________________________________________
__________________________________________________________________________________________________
__________________________________________________________________________________________________
In the table below, fill in the function of each of the four types of macromolecules.
Carbohydrates
Lipids
Proteins
Nucleic Acids
In the data table below, use your knowledge of types of food and their function, and make a prediction for if the
samples will provide a positive or negative reaction. Indicate your prediction by placing a “+” or “–“ in each box below.
A positive (+) reaction would indicate the presence of that macromolecule, while a negative (-) reaction would indicate
the lack of the macromolecule.
Data Table – Hypothesis
Sample
Simple Carbohydrate
(+ or -)
Complex
Carbohydrate (+ or -)
Protein
(+ or -)
Lipid
(+ or -)
Distilled Water
Procedure (Benedict’s Solution):
1. Based on the number of samples provided by your teacher, obtain the appropriate number of test tubes for
your lab station and label each with the name of the sample that you will be putting in each one.
2. Use a graduated cylinder to transfer 5 mL of distilled water into the appropriately labeled test tube.
3. Repeat step 2 for each of the samples provided by your teacher. (Each test tube should just have one sample.)
4. Add 10 drops of Benedict’s Solution to each test tube.
5. Gently shake the contents of each tube.
6. Place the test tubes in the hot water bath for 3-5 minutes. Remove the test tubes from the water bath using
test tube clamps (or other protective lab equipment to avoid touching the heated glass test tubes).
7. Review the indicator information from the beginning of the lab and record your data in the appropriate box in
your table.
8. If you will be reusing the same test tubes for additional tests, thoroughly wash each test tube.
Procedure (Iodine):
1. Based on the number of samples provided by your teacher, obtain the appropriate number of test tubes for
your lab station and label each with the name of the sample that you will be putting in each one.
2. Use a graduated cylinder to transfer 5 mL of distilled water into the appropriately labeled test tube.
3. Repeat step 2 for each of the samples provided by your teacher. (Each test tube should just have one sample.)
4. Add 5 drops of Iodine to each test tube.
5. Gently shake the contents of each tube.
6. Review the indicator information from the beginning of the lab and record your data in the appropriate box in
your table.
7. If you will be reusing the same test tubes for additional tests, thoroughly wash each test tube.
Procedure (Biuret Reagent):
1. Based on the number of samples provided by your teacher, obtain the appropriate number of test tubes for
your lab station and label each with the name of the sample that you will be putting in each one.
2. Use a graduated cylinder to transfer 5 mL of distilled water into the appropriately labeled test tube.
3. Repeat step 2 for each of the samples provided by your teacher. (Each test tube should just have one sample.)
4. Add 5 drops of Biuret Reagent to each test tube.
5. Gently shake the contents of each tube.
6. Review the indicator information from the beginning of the lab and record your data in the appropriate box in
your table.
7. If you will be reusing the same test tubes for additional tests, thoroughly wash each test tube.
Procedure (Sudan III):
1. Based on the number of samples provided by your teacher, obtain the appropriate number of test tubes for
your lab station and label each with the name of the sample that you will be putting in each one.
2. Use a graduated cylinder to transfer 5 mL of distilled water into the appropriately labeled test tube.
3. Repeat step 2 for each of the samples provided by your teacher. (Each test tube should just have one sample.)
4. Add 5 drops of Sudan III to each test tube.
5. Gently shake the contents of each tube.
6. Review the indicator information from the beginning of the lab and record your data in the appropriate box in
your table.
7. If you will be reusing the same test tubes for additional tests, thoroughly wash each test tube.
Data Table – Results
Sample
Simple Carbohydrate
(+ or -)
Complex
Carbohydrate (+ or -)
Protein
(+ or -)
Lipid
(+ or -)
Distilled Water
Data Analysis:
Summarize your findings in a 5-6 sentence paragraph below clearly indicating which samples contained which
macromolecules. (Do not simply state your results, utilize transition words and complete sentences.)
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
How did your results compare to your hypothesis? Did you correctly predict every sample? Were there some
samples where the results surprised you? (Do not simply answer the questions, elaborate and describe.)
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
_______________________________________________________________________________________________
Post Lab Questions:
1. A strong result for a Benedict’s Solution test would be to see the sample turn from blue to dark orange or
brown. If you had an unknown sample that you were testing that turned from blue to brown after heating for 35 minutes, which numbered structure below would you know was found in that sample? __________________
2. A strong result for a Sudan III test would be to see the sample turn red and under close examination you would
be able to see the small molecules in which the Sudan III dissolved. If you had an unknown sample that you
were testing that showed a positive reaction after being treated with Sudan III, which of the numbered
structures below would you know was found in that sample? ____________________
3. Imagine you had an unknown sample and while completing a test with Iodine, your sample turned from brown
to a dark purple. Which of the boxed structures below would be present in the sample? _______________
4. What is the difference in the two numbered structures below?
___________________________________________________________________________________________
___________________________________________________________________________________________
(1)
(2)
5. In the beginning of the lab, we discussed that the prefix macro- means large. You many also know that
macromolecules are also sometimes called polymers. The prefix poly- means “many” and a polymer is a
molecule that is made up on many smaller parts. The “many smaller parts” that make up a polymer are called
monomers, and the prefix mono- means one. One way in which you can identify the structure of a
macromolecule is to identify the numerous small parts (monomers) that make up the large molecule (polymer).
What is the name of the monomer of a protein? ____________________________. Which of the following
numbered structures below shows the monomer of a protein?
(1)
(2)
(3)
(4)