A DNA model project is a common science assignment that is also a lot of fun. Whether you make edible DNA models using candy or choose other everyday materials, you get hands-on experience with DNA structure and base pairing. Plus, if you’ve ever priced DNA model kits, you know you save a ton of money! Here are step-by-step instructions for construction three easy DNA models. Also, there are options for material substitutions and tips for expanding your learning with the model.
What Is DNA?
DNA is a biological macromolecule that codes the genetic information for life. In eukaryotes, like plants and animals, DNA is the cell nucleus. In prokaryotes, like bacteria, DNA is in a special region of the cell’s cytoplasm. The shape of DNA is a double helix, which resembles a twisted ladder. The rails or backbone of the “ladder” are alternating five-carbon sugar (deoxyribose) and phosphate residues. The “rungs” of the ladder are nitrogenous bases: adenine, thymine, guanine, and cytosine. Adenine and guanine are types of bases called purines. Thymine and cytosine are bases called pyrimidines. Adenine always pairs with thymine, while guanine always pairs with cytosine.
Method #1: Edible DNA Model Using Candy
You only need a few simple ingredients for an edible DNA model:
- Licorice sticks or ropes (Twizzlers)
- Colored gummy candies or marshmallows
- First, construct the backbone by cutting or assembling two equal lengths of licorice. Use either a single color of licorice for the sugar and phosphate backbone or else use both red and black licorice, but cut into small bars (each about 2 inches long) to represent the alternating components. If using two colors, connect alternating colored bits using toothpicks.
- Second, assemble the base pairs. You need four colors of candies or marshmallows for adenine, thymine, guanine, and cytosine. Set aside or eat any extra colors. Using toothpicks, connect adenine (A) to thymine (T) and guanine (G) to cytosine (C). These are the nucleotide base pairs.
- Third, connect the candy or marshmallow base pairs to the licorice. If using two colors of licorice, the base pairs connect to the color that represents the sugar, deoxyribose.
- Fourth, gently twist the licorice backbone and make a double-helix shape. If you over-twist the licorice, it maintains a helix shape when you relax your grip. Another way of securing the double helix is by fixing the top and bottom licorice pieces to cardboard or foam boards using toothpicks.
Method #2: DNA Model Using Pipe Cleaners
Pipe cleaners or chenille craft sticks are a good alternative to licorice for making the double helix ladder. Although they are technically wire, the fuzzy coating helps hold “base pairs” in place. Plus, scissors easily snip them apart.
- Colored candies, marshmallows, large-hole beads (pony beads), balls of clay, etc.
- You need two long pipe cleaners for the backbone. Think about whether you want to indicate the sugar and phosphate groups or not. If you do, snipping and joining small bits of pipe cleaner is unnecessary. Just use light-colored pipe cleaners and use a marker to draw the alternating sections.
- Cut smaller lengths for the base pairs. Use four colors of candies, beads, or clay for A, T, G, C. Make A-T and G-C. String or mold the base pairs onto the short pipe cleaner lengths. Curl both ends of each length into hooks for attaching them to the “backbone”.
- Connect the base pairs to the backbone.
- Gently twist the backbone and make the double helix form. Since pipe cleaners are wire, the DNA holds its shape.
Instead of using cut pipe cleaner pieces for the base pairs, an alternative is gluing base pair pieces together. Then, glue the base pairs to the two long pipe cleaners.
Another option for base pairs is using four pipe cleaner colors (no beads, candies, etc.). Cut each color into small pieces. Join the adenine piece to the thymine piece and the guanine piece to the cytosine piece. Bend the ends of pipe cleaner base pairs and attach them to the backbone.
Method #3: DNA Model Using Tape
If working with wire isn’t your thing, just use tape. Black electrical tape or other colored tape gives a better effect than clear tape. But, you can always color clear tape with markers, so use whatever is handy.
- Colored candies, marshmallows, beads, etc.
- First, make the base pairs. String A-T and G-C pairs of candies, beads, or whatever you have onto toothpicks.
- Cut two long strips of tape for the sugar and phosphate backbone. Place the pieces of tape sticky side up and parallel to each other. Leave enough space between the two strips for the base pairs.
- Line up the base pairs between the pieces of tape. The toothpicks should only reach about halfway across each strip.
- Fold each piece of tape in half vertically so that it covers the toothpick ends. The tape sticks to itself, leaving a smooth backbone.
- Twist the model and form the double helix.
Collect your own DNA and apply basic lab techniques so you can see it.
Tips for Further Study
- Identify the type of DNA of your model. DNA takes three forms: A, B, and Z. B DNA is the usual shape. It is right-handed DNA and forms major (wider) and minor (narrower) grooves between its base pairs. A DNA is a thicker right-handed helix that only has a short distance between subsequent base pairs. Z DNA is a left-handed helix. Only a small amount of Z DNA exists in nature, usually in stretches of alternating purines and pyrimidines. (e.g., CGCGCG).
- Either make more than one model or else compare models made by different people. Do you see the differences between the models? DNA comes in a variety of lengths and the possible orders of the base pairs is practically infinite!
- Why do you think DNA preferentially forms a double helix? When DNA replicates for making new cells, the molecule splits apart between the base pairs. Complementary bases fill in the broken region until two complete molecules form.
- Alberts, B.; Johnson, A.; Lewis, J.; Raff, M.; Roberts, K.; Walter, P. (2014). Molecular Biology of the Cell (6th ed.). Garland. ISBN 978-0-8153-4432-2.
- Berg, J.; Tymoczko, J.; Stryer, L. (2002). Biochemistry. W.H. Freeman and Company. ISBN 0-7167-4955-6.
- Berry, A.; Watson, J. (2003). DNA: The Secret of Life. New York: Alfred A. Knopf. ISBN 0-375-41546-7.
- Oh, D.B.; Kim, Y.G.; Rich, A. (2002). “Z-DNA-binding proteins can act as potent effectors of gene expression in vivo”. Proceedings of the National Academy of Sciences of the United States of America. 99 (26): 16666–71. doi:10.1073/pnas.262672699
- Wahl, M.C.; Sundaralingam, M. (1997). “Crystal structures of A-DNA duplexes”. Biopolymers. 44 (1): 45–63. doi:10.1002/(SICI)1097-0282(1997)44:1<45::AID-BIP4>3.0.CO;2-#