Science Courses

Sweet Science DNA

Sweet Science of DNA

by  Al Hazari


What do you think a single strand of DNA looks like? When DNA is taken out of the cell and stretched out, it looks like a twisted ladder — a shape called a double helix.  The sides of the DNA ladder are called the backbone, and the steps are pairs of small chemicals called bases. There are four types of bases in DNA: Adenine (A), Cytosine (C), Guanine (G) and Thymine (T). DNA bases follow certain rules when they form. Adenine (A) always pairs with Thymine (T), and Guanine (G) always pairs with Cytosine (C).

Using colored mini-marshmallows, licorice strips, and toothpicks,
you can construct your own DNA double helix. Two licorice pieces will be the backbones and the marshmallows and toothpicks will be the bases.

Safety Suggestions

• Be careful not to poke yourself or others with the toothpicks.

• Do not eat any of the materials used in this activit



• 2 licorice strips
• 16 colored mini-marshmallows (4 each of 4 different colors) • 8 toothpicks


Use the following color coding for marshmallows: A = green; T = pink; C = yellow; G = orange.

  1. Place both pieces of licorice on a flat surface (a table or the floor).

  2. Put together one side of your DNA double helix using this sequence

(from top to bottom): T A G A C T C G. To do this, place one marshmallow that matches the correct base (using the color codes above) on the end of toothpick.

  1. Push them in about 1⁄2 inch from the end.

  2. Then, stick the toothpick into the left licorice.

  3. Repeat this for the next several toothpicks, following the order above.

Space the toothpicks about 3⁄4 inch apart from each other.

  1. Match the chemical base pairs by placing the colored marshmallow for

the chemical base on the other end of each toothpick. Remember, A (green) always pairs with T (pink) and C (yellow) always pairs with G (orange). For example, place a green marshmallow on the other end of a toothpick with a pink marshmallow, and a yellow marshmallow on the other end of a toothpick with an orange marshmallow.

  1. Complete your DNA double helix by attaching the other backbone (right licorice).

  2. Carefully twist your DNA until it looks like the picture above.


What did you see?

• When you attach both backbones, what does it look like?

• What is the shape of DNA called when you twist it?


Where’s the chemistry?

DNA is what makes living things look, and sometimes behave, the way they do — from birth, through growth and death. When chemists discovered DNA, it changed science and medicine forever. It has also affected many other parts of our lives. For example, it helps to explain why people look the way they do, gives police tools for finding criminals, and much more.

DNA is also important in our own lives. First, it carries hereditary information from generation to generation. Second, it controls the production of proteins and the structures of cells. That means DNA can determine whether a cell will become part of a nerve, a muscle, or even an eyeball. When it comes to forensic science and its uses, DNA is also important. Because each person’s DNA is one-of-a-kind, even a small sample of it can be used to positively identify an unknown person.