Make a Model DNA Strand

Summary

A strand of DNA looks like a ladder that has been twisted into a corkscrew. Just like a ladder, a DNA strand has two rails running parallel to each other and rungs that connect the rails.

The rails of the DNA strand are made up of deoxyribose (a sugar) and phosphoric acid. These two molecules alternate one after the other the entire length of the rail.

The rungs of the DNA strand are made up of organic bases. These organic bases attach to the deoxyribose on the ladder rails. The four bases that make up DNA are Adenine, Thymine, Cytosine, and Guanine. These bases are abbreviated as A, T, C, and G. Each rung of a DNA strand contains two bases that are paired together. Each base has a specific partner that it pairs with. Adenine always pairs with Thymine and Cytosine always pairs with Guanine. (Remember AT and CG). In this activity, you will build two DNA models. Both models represent the major components of a strand DNA.

In this activity we will:

• Build a model DNA strand.
• Analyze the model to see what each of the components represents.
• Analyze the model to see what properties of actual DNA are not represented

Materials

• 2 pieces of regular Twizzlers
• 1 bag of medium Gummy Bears
• 1 box of round toothpicks

Safety

This activity requires the use of sharp toothpicks. Use caution when working with the toothpicks. These toothpicks can puncture your skin if not handled properly. Ask an adult to help you if necessary.

Preparation

• Gather all materials listed above before beginning

Activity

• Take out four red, four clear, four yellow, and four green Gummy Bears.
• Carefully thread a green and clear Gummy Bear onto a toothpick. (Be careful to not poke your fingers while doing this). The Gummy Bears should touch each other and meet in the middle of the toothpick leaving extra space on either side of the toothpick.
• Continue to thread one green Gummy Bear with one clear Gummy Bear until all green and clear colors are paired.
• Thread the red Gummy Bears with the yellow Gummy Bears the same way that you did with the green and clear. You should now have 8 pairs of Gummy Bears threaded onto toothpicks.
• Take the one pair of Gummy Bears and press one end of the toothpick into a strand of Twizzlers. It does not matter which toothpick is used.
• Take the remaining pairs of Gummy Bears and stick them into the strand of
• Twizzlers as done in the previous step. Leave about one inch in between each pair of Gummy Bears.
• Connect a second strand of Twizzlers to the other end of the toothpicks.
• You should now have a ladder with eight rungs.

Wrap-up

Remember that DNA is shaped like a corkscrew. To get this shape, twist the model that you made to get a better idea of what DNA looks like. The shape that you just made is referred to as a double helix.

Each Gummy Bear in the model represents a base. The Green represents Guanine and the Clear represents Cytosine. What two bases do the other two colors represent?

This model is missing a component. Which component is missing? Read through the summary if you need help with this question. (Answer is at the end of this activity).

Answers

Model: This model does not show the two individual components that make up the rails of the DNA strand. Remember that the rails of a DNA strand contain repeating molecules of deoxyribose (a sugar) and phosphoric acid.

Resources

http://nobel.scas.bcit.ca/resource/dna/dna_sweets.htm

http://school.discovery.com/lessonplans/programs/modeldna

http://learn.genetics.utah.edu/units/basics/builddna/ (Great Animation Site)

Download the PDF for an additional Model built from pipe cleaners, string, and pasta

Activity PDF: dna_strand_model.pdf