DNA Candy Modeling - College of Science and Mathematics ...

DNA Candy Modeling
Contributors
Bradley Wilbur
Graduate Student
Georgia Southern University, GA
Yvonne Arnsdorff
Partner Teacher
Effingham County High School, GA
Intended Audience
K-4
5-8 X
9-12 X
Intended Audience
Classroom Setting x
Requires special equipment
Uses hands‐on manipulatives X
Requires mathematical skills
Can be performed individually x
Requires group work
Requires more than one (45 min class) period
Appropriate for special needs student x
Janee Cardell
MBI Program Coordinator
P.O. Box 8042
Statesboro, GA 30460
jcardell@georgiasouthern.edu
DNA Candy Modeling – Page 1

Introduction
Description
The manipulation of candy pieces to model the molecular structure of DNA.
Abstract
Students will use marshmallows, gummy bears, and toothpicks to model the structure of DNA.
This procedure differs from similar activities by showing students the distinction between
deoxyribose and phosphate groups and how they alternate along the backbone. Students
replicate one strand of DNA twice, yielding 2 double-stranded DNA molecules. This
exemplifies complementarity and anti-parallelism. The modular construction of the DNA model
helps to reinforce the concept of DNA as a macromolecule.
Core Themes Addressed
Microbial Cell Biology
Microbial Genetics X
Microorganisms and Humans
Microorganisms and the Environment
Microbial Evolution and Diversity
Other -specify
Keywords
Complementary Pairing
Replication
Percent Composition
Learning Objectives
At completion of this activity, learner will
1. Demonstrate proper pairing between nitrogenous bases.
2. Simulate accurate replication of both DNA strands.
3. Analyze percent composition of a DNA sample.
4. Differentiate between covalent and hydrogen bonds in DNA.
DNA Candy Modeling – Page 2

National Science Education Standards Addressed
Standard C: Life Science – This activity addresses the molecular basis of heredity by describing the
structure of DNA and its role in organisms.
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Student Prior Knowledge
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Teacher Handout
DNA Candy Modeling
Students do not need any prior knowledge of DNA to complete this activity. However, they may have
some information already regarding DNA’s role as the molecule of inheritance and unique identification
of individuals. Asking questions about DNA that they can answer from general knowledge may help to
get them excited about the day’s activity.
Teacher Background Information
Instructor needs to be familiar with the structure of DNA in order to help students through the concepts of
base-pairing, complementarity, and anti-parallelism. This activity is neither physically demanding nor
skill-based.
Class Time
This activity will require a minimum of one 45-minute class period
1. Students will need to collect materials and return to their seats/stations. This should take 3-5 minutes
depending on class size.
2. Students will follow the instructions to create their DNA strands. This should take 20-30 minutes.
3. Students will answer the questions on the handout. This should take 5-10 minutes.
Teacher Preparation Time
This lesson will require approximately 5 minutes of preparation time.
1. Materials must be laid out so that students can collect them efficiently.
2. Lay down paper towels on work surfaces if the intent is for students to consume the models outside the
lab.
Safety Precautions
If consumption of models is anticipated, ensure proper hand-washing and covering of work surfaces.

Materials and Equipment
Each student or group of students (up to 4/group) will require the following:
Methods
1. 32 large marshmallows
2. 32 small marshmallows
3. 32 gummy bears, 8 of each color (4 colors)
4. 96 wooden toothpicks
5. 16 plastic or colored toothpicks
1. Link large and small marshmallows together in an alternating pattern using the
wooden toothpicks. 8 of each type of marshmallow will be needed for 1 completed
backbone (of which there will be 4).
2. Link the appropriate colored gummy bear to each large marshmallow using a wooden
toothpick. The sequence can be anything of your choosing (ATGACTCG works
well). Make sure there is a color code for the students to see.
3. Combine the two strands by linking gummy bears from opposite strands with colored
or plastic toothpicks. Make sure the bases are paired correctly (A – T, C – G)
4. With one double-stranded molecule complete, initiate replication by splitting the
strands apart. Link new complementary strands to the old strands as you go along.
5. You should end with 2 double-stranded DNA molecules which are identical to each
other.
Tips/Suggestions
References
1. This also works with twizzlers as the backbone instead of marshmallows. This cuts down on
toothpick usage.
This activity was modified from Derek Tucker of the Georgia Southern University MBI
Program.
Extension/Additional Resources
http://biology.about.com/od/biologylabhowtos/ht/dnamodelcandy.htm - Alternate method of
creating DNA models out of candy. Accessed 12/3/2011
DNA Candy Modeling – Page 5

Answers to Student Handouts
1. Sketch one of your double-stranded DNA molecules. Label the bases A, T, C, and G, as well
as a deoxyribose sugar and a phosphate group. Label the 5’ and 3’ ends of both strands.
2. Using base complementarity rules, if I have a sample of Sculpin DNA that is 23% Cytosine,
what is the approximate percent composition for each of the other bases?
G: 23%
A: 17%
T: 17%
3. During DNA Replication, the old DNA strand serves as a template for the new strand. What
does this mean?
The information on the old strand is used to determine the sequence of the new strand.
4. DNA Replication is not 100% accurate in the cell. Sometimes the wrong bases are paired up,
like C with T. What do you think happens in response when this occurs? If it doesn’t get fixed,
what might the consequences be for the new cell receiving this DNA?
Nucleotide Excision Repair processes remove incorrectly-paired areas of DNA and replace it
with the correct bases. If incorrect pairing is not fixed, mutations can arise which negatively
affect the function of the cell.
5. DNA contains both hydrogen and covalent bonds. Which of these bonds is stronger, and
where can you find each of these in a DNA molecule?
Covalent bonds are stronger than hydrogen bonds. Covalent bonds are found in the DNA
backbone and link sugars and phosphates together. Hydrogen bonds form between base pairs
and hold the two strands together.
DNA Candy Modeling – Page 6

Introduction
DNA Candy Modeling – Page 7
Student Handout
DNA Candy Modeling
DNA stands for Deoxyribonucleic Acid, and it is a molecule found in every living cell, as well as
some viruses. DNA contains the blueprints for our bodies, determining how we look and partly
how our offspring will look. The molecular structure of DNA has been known since the 1950’s
and it is a very unique shape. Today’s activity will guide you through understanding the
different parts of the DNA molecule, how they all interact, and how it replicates itself. Be sure
to note the sequence of DNA that you are tasked with creating today.
Student Background Knowledge
Deoxyribose sugars and phosphate groups alternate to form the DNA’s backbone. A nitrogenous base is
attached to each deoxyribose to form the “rungs” of the DNA ladder. Nitrogenous bases always pair the
same way: A with T and C with G. DNA strands run anti-parallel, meaning that they are read in opposite
directions. When replicating, the old strand provide the information for the sequence of the new strand in
order to form a new double-helix.
Vocabulary
Anti-parallel strands: Two complementary DNA strands that run side-by-side but read in opposite
directions
DNA: Deoxyribonucleic acid, a molecule that carries genetic information in all living things.
Nitrogenous Base: Molecules such as adenosine or thymidine which are part of DNA. They give a DNA
strand its unique sequence, and bonds between them hold DNA double-helices together.
Semi-Conservative Replication: The process by which DNA is copied wherein a new DNA double-helix
is made of a parent strand and a daughter strand.
Safety Considerations
Be sure to wash your hands before handling food products and cover all work surfaces to avoid
contamination.
Some toothpicks can be unusually sharp, so use caution.

Materials Checklist
32 Large Marshmallows
32 Small Marshmallows
32 Gummy Bears, 8 of each color
96 Wooden Toothpicks
16 Plastic/colored toothpicks
Procedure
Results
1. Link large and small marshmallows together in an alternating pattern using the
wooden toothpicks. 8 of each type of marshmallow will be needed for 1 completed
backbone.
2. Link the appropriate colored gummy bear to each large marshmallow using a wooden
toothpick.
3. Combine the two strands by linking gummy bears from opposite strands with colored
or plastic toothpicks. Make sure the bases are paired correctly (A – T, C – G)
4. With one double-stranded molecule complete, initiate replication by splitting the
strands apart. Link new complementary strands to the old strands as you go along.
5. You should end with 2 double-stranded DNA molecules which are identical to each
other.
Use what you have learned from this activity to answer the accompanying questions about DNA.
DNA Candy Modeling – Page 8

Name: ______________________
Block:________
DNA Candy Modeling – Page 9
Student Worksheet
DNA Candy Modeling
DNA Candy Modeling Activity
1. Form groups of 4 individuals. Wash your hands before you work with food items.
2. Collect the following materials per group:
a. 32 large marshmallows
b. 32 small marshmallows
c. 32 gummy bears, 8 of each color
d. 100 Wooden Toothpicks
e. 16 Plastic Toothpicks
f. Paper Towels to cover the workspace
3. The large marshmallows represent deoxyribose sugars. The small marshmallows
represent the phosphate groups that link them together. The gummy bears represent
the 4 different nitrogenous bases. Wooden toothpicks represent covalent (strong)
bonds. Plastic toothpicks represent hydrogen (weak) bonds. Use your knowledge of
DNA structure to form a single strand of DNA with sequence: ATGACTCG Use the color
code on the board to determine which gummy bear represents which base.
4. Get approval before moving to the next step: Form the complementary strand to create
a double‐stranded DNA molecule. See if you can twist it to form a double helix.
5. Get approval before moving to the next step: Replicate your DNA. Pull apart the two
strands and build complementary strands for both of them.

6. Disassemble your DNA into single strands. Each student keeps a strand. Any unused
materials go back up front, not in your mouths.
7. Answer the following questions before you leave today:
1. Sketch one of your double‐stranded DNA molecules. Label the bases A, T, C, and G, as well
as a deoxyribose sugar and a phosphate group. Label the 5’ and 3’ ends of both strands.
2. Using base complementarity rules, if I have a sample of Sculpin DNA that is 23% Cytosine,
what is the approximate percent composition for each of the other bases?
G: _______
A: _______
T: _______
3. During DNA Replication, the old DNA strand serves as a template for the new strand. What
does this mean?
______________________________________________________________________________
______________________________________________________________________________
4. DNA Replication is not 100% accurate in the cell. Sometimes the wrong bases are paired up,
like C with T. What do you think happens in response when this occurs? If it doesn’t get fixed,
what might the consequences be for the new cell receiving this DNA?
______________________________________________________________________________
______________________________________________________________________________
DNA Candy Modeling – Page 10

5. DNA contains both hydrogen and covalent atomic bonds. Which of these bonds is stronger,
where can you find each of these in a DNA molecule, and what do they do in their respective
areas?
______________________________________________________________________________
______________________________________________________________________________
______________________________________________________________________________
DNA Candy Modeling – Page 11