You Are What You Eat: An Investigation
of Macromolecules
Student Materials
Introduction ................................................................................................................... 2
Lab Protocol ................................................................................................................... 5
Pre-Lab Questions .......................................................................................................... 10
Post-Lab Questions and Analysis .................................................................................... 11
Students
You should read the Introduction and Lab Protocol and then answer the Pre-Lab Questions. Also be
sure to answer the questions that are embedded in the Introduction. Completion of the questions will
help you understand the concepts and procedures of the lab. Once you have completed the lab,
answer the Post-Lab Questions and Analysis.
1
Introduction
When choosing food for lunch, do you ever consider the amount of protein, carbohydrates, and lipids (fats) in your choices?
Or maybe you think back to a version of the classic food pyramid: grains on the bottom, fats and sweets at the top, meat,
dairy, fruits, and vegetables in between. You probably know that grains like bread contain carbohydrates, but did you know
that is also is a source of protein? And did you ever think about the difference between whole wheat bread and white
bread? It’s fiber—a special kind of carbohydrate that helps with digestion. Working up the pyramid, tuna fish, hamburger,
and turkey slices contain protein, but did you know that they also contain some fat? Dairy products contain protein, too,
but they also contain carbohydrates in the form of milk sugars. There is fat in dairy, too, unless you opt for nonfat yogurt of
skim milk. You know what else contains fat and protein? A plum! Surprised? You shouldn’t be! Vegans don’t eat animal
products, not even dairy and eggs, but they still manage to get protein—it’s just protein that comes from plants instead of
animals. Tofu, which is made from soybeans, is full of protein, as are legumes, such as beans and lentils. Legumes have a lot
of fiber, too, as do fruits and vegetables. Chocolate is a sweet and has fat, but it also has carbohydrates, fiber, and protein!
On top of all of this, guess what else you’re eating every time you eat a product that comes from plants or animals? DNA
and RNA! That old food pyramid is looking a bit more complicated now, isn’t it?
Biochemistry of macromolecules
You may not have realized it, but how much protein, carbohydrate, fat, and fiber a food contains all comes down to
biochemistry. So as we explore macromolecules in this lab, remember: you already know a lot. Much of our food comes
directly from plants and animals. Plants and animals are composed of cells, and all cells have four major types of large,
complex molecules called macromolecules: carbohydrates, proteins, lipids, and nucleic acids.
Say you have 1 cup of tuna fish and 1 cup of strawberries for lunch. Both foods are composed of cells and all
cells have protein, carbohydrates, lipids, and nucleic acids.
Which of these macromolecules contain carbon? ___________________________________________
Which of these macromolecules contain nitrogen? _________________________________________
Which of these macromolecules contain phosphorus? _______________________________________
If the tuna fish and the strawberries are both composed of cells, why do the protein and carbohydrate amounts
differ between the two snacks? _________________________________________________________
__________________________________________________________________________________
If you have taken ecology, you learned that nutrients cycle through the environment, but did you also know they cycled
within organisms? Plants are called primary producers (or autotrophs) because they produce their own carbohydrates
through photosynthesis using water, carbon dioxide, and energy from the sun. Plants also metabolize some of these
carbohydrates to supply energy and raw materials to synthesize complex carbohydrates, proteins, lipids, and nucleic acids
using nitrogen, phosphate, and trace elements acquired from the environment. Consumers (heterotrophs), which include
all organisms that aren’t capable of photosynthesis (including humans), have to rely on the environment for all of the raw
materials they need to build new cells. Most of these raw materials come from the macromolecules consumed in food.
These macromolecules get broken down through the processes of digestion and the resulting building blocks are used
directly or indirectly to form new materials needed for growth and development.
What is the name and chemical formula for the monosaccharide produced by photosynthesis?
__________________________________________________________________________________
What is the name of the process that plants use to metabolize carbohydrates to produce the energy they need to
synthesize other types of macromolecules? _______________________________________________
2
What is the name of the process that humans use to metabolize carbohydrates to produce the energy they need to
synthesize other types of macromolecules? _______________________________________________
Most macromolecules are made of repeating subunits called monomers. Since macromolecules are made of several
monomers they can be called polymers. When two monomers are joined together the chemical reaction is called
dehydration synthesis. The reaction involves the release of an OH– from one monomer and the release of an H+ from the
other. These ions join to form a water molecule. In addition to forming new polymers, cells also need to break down
polymers. This reaction is called hydrolysis. The hydrolytic reaction requires the addition of a water molecule and breaks
the bond between two monomers.
Dairy products contain the disaccharide lactose, which is made up of the monosaccharides galactose and glucose. The
overall formula for lactose is C12H22O11. When lactose forms, a molecule of water (H2O) is released. What is the
chemical formula for galactose? Hint! Think of the overall reaction: glucose + galactose  lactose + water. Fill in the
formulas you know and balance the equation. ___________________________________________
What do you notice about the chemical formulas for glucose and galactose? __________________
Testing for macromolecules
In this lab, you will use simple methods to test for the presence of carbohydrates, protein, lipids, and nucleic acid in lima
beans and corn. Carbohydrates are primarily used as a source of energy. Plants and some types of animals also use
carbohydrates for structure. Although all carbohydrates contain carbon, oxygen, and hydrogen, the chemical nature of
monosaccharides (simple sugars, monomers) and polysaccharides (complex sugars, polymers) differ, which makes it
possible for us to identify them with chemical tests. In this lab, you will use Benedict’s solution and iodine to test foods for
different carbohydrates. Monosaccharides will turn Benedict’s solution from blue to a red or rusty orange. Lugol’s solution’s
(iodine) changes from dark red to blue-black when it is mixed with the polysaccharide, starch.
Proteins are used in cells in a variety of ways, including as enzymes, structural components, and signaling. Some proteins
are composed of a single long polymer of amino acids called a polypeptide. Other proteins are composed of two or more
polypeptides. There are 20 different amino acids that can be joined together in any order and since amino acid chains can
vary greatly in length, polypeptides (and therefore proteins) are highly diverse. The order of amino acids in a polypeptide
dictates the structure and function of a protein. Proteins can be distinguished from other macromolecules using a chemical
called Biuret. This blue liquid will turn purple when mixed with proteins.
What do enzymes do? ________________________________________________________________
Nucleic acids are polymers of nucleotides. Each nucleotide is made up of a five-carbon sugar, a phosphate group, and a
base. DNA nucleotides contain the sugar deoxyribose while RNA nucleotides contain the sugar ribose. The bases adenine,
cytosine, guanine, and thymine (A, C, G, T) are found in DNA, while RNA contains adenine, cytosine, guanine, and uracil (A,
C, G, U). The primary function of nucleic acids is information storage and transmission. DNA provides the information
needed for the cell to make proteins. A gene is a small segment of a chromosome that contains the information to make
one polypeptide. So when you hear the words chromosome or gene, you should be thinking about DNA! Together, DNA and
RNA contain all of the blueprints and instructions for all of life’s processes. SYBR Safe solution contains a molecule that
binds to DNA and causes it to glow green when viewed under a UV light.
Lipids are used for energy storage and structural components of the cell. Lipids are a large and diverse group of molecules
that are primarily composed of long chains of hydrogen and carbon. They are non-polar (hydrophobic) molecules so they do
not mix with water Lipids are a not composed of repeating subunits, so they are not really polymers. Modified lipids called
phospholipids are the major component of the plasma membrane and are critical to cells. Lipids can be tested with Sudan
IV. Like lipids, Sudan IV is hydrophobic. When mixed with a watery solution, Sudan IV and lipids will form a separate brightred layer.
Given what you know about lipids, explain why your salad dressing separates?___________________
3
You Are What You Eat: An Investigation of Macromolecules
Lab Protocol
Materials:
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1  p200 micropipettor and pipette tips
2  microcentrifuge tubes
8  test tubes
1  test tube rack
4–10  transfer pipettes
permanent marker (such as Sharpie)
distilled water
BSA (protein) solution
Biuret solution
glucose solution
Benedict’s solution
boiling hot water bath
starch solution
Lugol’s solution
vegetable oil
ethanol
Sudan IV
lambda DNA
SYBR Safe solution
UV light source
lima bean solution
corn solution
Procedure:
Make the control solutions
Important! Safety goggles should be worn throughout this lab.
1. Use a permanent marker to label the 8 test tubes and 2 microcentrifuge tubes according to Table 1.
2. Using a clean transfer pipette, put approximately 2 mL of distilled water into each of the negative control test tubes (P–,
G–, S–, L–)
3. Using a 200-μL micropipette, put approximately 25 μL of distilled water into the negative control microcentrifuge tube
(NA–).
Protein positive (P+) and negative (P–) controls
4. Using a clean transfer pipette, put approximately 2 mL of BSA solution into the P+ test tube.
5. Add 5 drops of Biuret reagent to the P+ and P– tubes. Hold the tubes over white paper and examine. Record the color in
Table 1.
Glucose positive (G+) and negative (G–) controls
6. Using a clean transfer pipette, put approximately 2 mL of glucose solution into the C/G+ test tube.
4
7. Add 1 mL of Benedict’s solution to the G+ and G– tubes. Carefully place the test tubes in a boiling hot water bath. Wait 3-4
minutes. Using tongs or a test tube holder to protect your hand, remove the test tubes from the water bath and place them
in a test tube rack. Caution! Be very careful when handling the test tubes, they will be hot. Record the color in Table 1.
Starch positive (S+) and negative (S–) controls
8. Using a clean transfer pipette, put approximately 2 mL of starch solution into the S+ test tube.
9. Add 3 drops of Lugol’s solution to the S+ and S– tubes. Record the color in Table 1.
Lipid positive (L+) and negative (L–) controls
10. Using a clean transfer pipette, put approximately 1 mL of distilled water into the L+ test tube.
11. Using a clean transfer pipette, put approximately 0.5 mL of vegetable oil into the L+ test tube.
11. Slowly add 1 mL of ethanol to the L+ and L– test tubes by letting the ethanol run down the side of the test tube. Add 3
drops of Sudan IV to both test tubes. Wait 4–5 minutes. Record the color in Table 1.
Nucleic acid positive (NA+) and negative (NA–) controls
12. Using a p200 micropipette and clean pipette tip, place approximately 25 μL of Lambda DNA to the NA+ tube.
13. Using a clean pipette tip, add 25 μL of SYBR Safe solution to NA+ and NA– tubes. Important! Be sure to use a new tip for
each test solution. Gently mix the solutions and observe them under a UV light. Caution! Use the appropriate protective
gear when using a UV light. Record the color in Table 1.
14. Put all 10 of these controls aside in a safe location. You will use these tubes for your standard tests and should keep
them for comparison throughout the lab.
5
Table 1. Control Solutions
Label
Contents
Test Reagent
Positive control,
protein
P+
BSA solution
(protein)
Biuret solution
Negative control,
protein
P–
distilled water
Biuret solution
Positive control,
glucose and other
monosaccharides
G+
glucose
solution
Benedict’s solution
Negative control,
glucose and other
monosaccharides
G–
distilled water
Benedict’s solution
Positive control,
starch and other
polysaccharides
S+
starch solution
Lugol’s solution
Negative control,
starch and other
polysaccharides
S–
distilled water
Lugol’s solution
Positive control,
lipids
L+
vegetable oil
Sudan IV solution
Negative control,
lipids
L–
distilled water
Sudan IV solution
Positive control,
nucleic acids
NA+
Lambda DNA
SYBR Safe solution
NA–
distilled water
SYBR Safe solution
Color Observed
*(microcentrifuge tube)
Negative control,
nucleic acids
*(microcentrifuge tube)
6
Testing the seed samples
1. Before testing, predict which compounds will be found in each food. Indicate your predictions in Table 2. Use (+) to
indicate predicted presence and (–) to indicate predicted absence.
2. Use a permanent marker to label the 8 test tubes and 2 microcentrifuge tubes according to Table 2.
3. Using a clean transfer pipette, put approximately 2 mL of lima bean solution into each of the lima bean (LB) test tubes.
4. Using a p200 micropipette, put approximately 25 μL of lima bean solution into the NA/LB tube and the NA/C tube.
5. Using a clean transfer pipette, put approximately 2 mL of corn solution into each of the corn (C) test tubes.
5. Using a p200 micropipette, put approximately 25 μL of corn solution into the NA/C tube.
6. Add 5 drops of Biuret reagent to the P/LB and P/C tubes. Hold the tubes over white paper and examine. Record the color
in Table 2.
7. Add 1 mL of Benedict’s solution to the G/LB and G/C tubes. Carefully place the test tubes in a boiling hot water bath.
Wait 3-4minutes. Using tongs or a test tube holder to protect your hand, remove the test tubes from the water bath and
place them in a test tube rack. Caution! Be very careful when handling the test tubes, they will be hot. Record the color in
Table 2.
8. Add 3 drops of Lugol’s solution to the S/LB and S/C tubes. Record the color on the Table 2.
9. Slowly add 1 mL of ethanol to the Lipid LB and Lipid C test tubes by letting the ethanol run down the side of the tube. Add
3 drops of Sudan IV to both test tubes. Wait 4–5 minutes. Record the color and the location of the color in Table 2.
10. Add 25 μL of SYBR Safe solution to NA/LB and NA/C tubes. Important! Be sure to use a new tip for each test solution.
Gently mix the solutions and observe them under a UV light. Caution! Use the appropriate protective gear when using a UV
light. Record the color in Table 2.
11. Clean and dispose of materials as directed by your instructor.
7
Table 2: Seed Tests
Label
Test
Solution
Test Reagent
Protein,
lima bean
P/LB
lima bean
Biuret
solution
Protein,
corn
P/C
corn
Biuret
solution
Glucose,
lima bean
G/LB
lima bean
Benedict’s
solution
Glucose,
corn
G/C
corn
Benedict’s
solution
Starch,
lima bean
S/LB
lima bean
Lugol’s
solution
Starch,
corn
S/C
corn
Lugol’s
solution
Lipid,
lima bean
L/LB
lima bean
Sudan IV
solution
Lipid,
corn
L /C
corn
Sudan IV
solution
Nucleic acid,
lima bean
NA/LB
lima bean
SYBR Safe
solution
NA/C
corn
SYBR Safe
solution
Prediction
(+/–)
Results
*(microcentrifuge tube)
Nucleic acid,
corn
*(microcentrifuge tube)
8
You Are What You Eat: An Investigation of Macromolecules
Pre-Lab Questions
Directions: After reading through the introduction and protocol for the macromolecule lab, answer the questions below.
1. Remembering What are the four primary types of macromolecules?
2. Understanding You read somewhere that having a protein-rich breakfast can help combat fatigue and improve test
performance. Which of the following would make the best breakfast option the morning of a big exam: toast with butter
and jam OR an omelet with black beans and cheese? Justify your answer.
3. Understanding Why are plants called “producers” and other organisms called “consumers”?
4. Applying Look at the diagram below. Identify:
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the type of macromolecule, monomer, and polymer involved; and
whether the reaction is a dehydration reaction or a hydrolysis reaction.
Wikicommons
5. Remembering Match the following indicators with the type of macromolecule they will be used to test:
1. Benedict’s solution
a. Carbohydrates—monosaccharides
2. Biuret solution
b. Carbohydrate—polysaccharides
3. Lugol’s solution
c. Lipids
4. Sudan IV solution
d. Nucleic acids
5. SYBR Safe solution
e. Proteins
9
You Are What You Eat: An Investigation of Macromolecules
Post-Lab Questions and Analysis
Directions: After completing the macromolecules lab, answer the questions below.
1. Analyzing How did your predictions match up against your results? Did you get any unexpected results?
2. Applying The nutrition label below came from either a can of corn or a can of lima beans. Which is it? Can you tell?
Explain your answer.
3. Applying The nutritional information for fresh strawberries is below. Notice that there is no fat (Total Fat = 0g) in a
serving of 8 medium berries. Your friend concludes that strawberries are “fat free.” Explain why that isn’t true.
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