Inside DNA
Time: Part I: 20 minutes
Part II: 30 minutes
Discussion: 10 minutes
Materials (per pair)
Part I
6 black licorice pieces
6 red licorice pieces
6 gumdrops
2 6” pieces of wire
6 toothpicks
Scissors
Part II
Half a set of licorice, gumdrops,
wire, and toothpicks
Colored pencils that match
gumdrop colors
Printer paper
Background:
*Explain this to the class; draw the DNA structure on the board or show on an Elmo.
Your body is made up of genes, and genes are made up of a substance called DNA. DNA
stands for deoxyribonucleic acid (dee-oxee-rye-bow-new-clay-ick acid), and it contains a
set of instructions for building a human. When isolated from a cell and stretched out, DNA
looks like a twisted ladder. This shape is called a double helix. The sides of the DNA ladder
are called the backbone and the steps (also called rungs) of the ladder are pairs of small
chemicals called bases. There are four types of chemical bases in DNA:
Adenine (A)
Guanine (G)
Cytosine (C)
Thymine (T)
These chemical bases form pairs in very specific ways. Adenine (A) always pairs with
Thymine (T) and Cytosine (C) always pairs with Guanine (G).
Some parts of your DNA are control centers for turning genes on and off and others contain
instructions for building proteins, which help build an organism. Some parts of DNA have a
function that we don’t understand yet, and other parts have no function at all!
Directions:
Part I—Build DNA
1. Direct students to find a partner. Have one person from each
group come up and get their materials.
2. Explain to them what each material stands for. The red
licorice pieces are sugars and the black licorice pieces are
phosphates. These are the chemicals that make up DNA.
3. Put the red and black licorice pieces onto the wire, alternating
colors. Have them bend the tip of the wire so the pieces don’t
fall off the bottom. It should look like the picture at the right.
4. Tell the students to make 3 base pairs. They can do this by
joining each pair of gumdrops with two toothpicks as shown
below. Each color should only pair with one other color (eg.
blue with red, green with yellow).
5. Make the DNA ladder by connecting the backbone with the
toothpicks. Toothpicks should only be connected to the red
(sugar) sections.
6. Double check your DNA to make sure there is not a
mutation. Mutations are mistakes in the DNA structure.
Part II—Make a Gene and Copy It
1. Tell each team to pair up with another team. The teams should connect their DNA
sections together by hooking the wire ends together. The connected DNA forms a
gene.
2. Students should use colored pencils to draw your gene, making sure to match the
colors with the gumdrop colors.
3. Have students assign a letter to each of the colored gumdrops (A, T, C, or G).
Remember that Adenine (A) always pairs with Thymine (T) and Cytosine (C) always
pairs with Guanine (G). Record which color is which letter on your drawing.
4. Genes are described by using those four letters. Have students describe their gene
by writing the letters in the correct order. Only use one side (dashed area above).
5. DNA copies itself by splitting down the middle and
making another half of itself. Tell students to
CAREFULLY pull their DNA strand in half so one
gumdrop and one toothpick are attached to each
side. You may need to demonstrate this.
6. Tell the students to split back into their original
pairs. Their challenge is to replicate the original
gene. Have one student from each pair come up and
collect half a set of materials, making sure to match
the gumdrop colors correctly.
7. Have each team replicate their DNA strand.
*Working on a flat surface is helpful.
8. When the teams are finishes, have students compare their gene to the drawing. Is it
an exact copy? If not, what do you think that would mean to the owner of the DNA?
Discussion:
Ask the students the following questions and let them guess the answers. Once you reveal
the answer, see what their response is. Ask them if they were surprised or not, and why.
Q: How similar do you think your DNA is to your partner’s? To chimpanzees? Mice? To a
banana?
A: The DNA in all humans is 99.9% identical. We share 98% of our DNA with chimpanzees
and 90% with mice. Human DNA is 50% identical to a banana’s.
Q: If you were to stretch out the DNA in one cell and lay it end to end, how long do you
think it would be? How about the DNA in your entire body?
A: The DNA in one cell would be over 2 yards (around 10 feet) in length. The DNA from an
entire person could reach to the sun and back over 30 times. The sun is 93 million miles
away, making one person’s entire DNA over 2.79 billion miles long.
Q: How big do you think DNA is?
A: You could fit one million threads of DNA across the period at the end of this sentence.
Q: How long do you think it takes for one of your cells to completely copy its DNA?
A: About 8 hours
Q: How long do you think it would take to recite the order of the ATCGs in your DNA?
A: At a rate of 100 letters per minute, it would take 57 years to recite (providing you did
not sleep, eat, use the bathroom, etc.).