In this activity you will make a candy model of the DNA (deoxyribonucleic acid) polymer. The final product will look like a ladder with licorice side rails and squishy candy rungs, all held together with toothpicks. I will be using marshmallows for the squishy candy, but you can choose any candy you can stick a toothpick into!
Supplies:
2 licorice twists
5 toothpicks
10 colored marshmallows or other squishy candies
Instructions:
1) Take a look at your candy color options. The candies represent molecules called “bases”. These bases are named adenine, guanine, cytosine and thymine. Usually adenine and thymine (A-T) pair together, while cytosine and guanine (C-G) pair together. You can decide which candy color will represent each of the four bases.
2) Push one squishy candy onto each end of a toothpick. I am using marshmallows, but you might be using something different. Fruit snacks? Gummy bears? Candy corn? Rolos? Starburst?
3) Repeat 4 more times until you have 5 base pairs. You can decide whether you will make wild type DNA (A-T and C-G pairs) or mutant DNA (a different combination of pairs).
4) Place 2 pieces of licorice side by side on a table in front of you. Move them apart far enough to arrange your candy base pairs between the licorice pieces, so the structure looks like a ladder.
5) Push the toothpick ends into the licorice twists to fit your ladder together.
6) Now you need to turn your ladder into a double helix. Hang on to both ends and give a gentle twist in opposite directions. Show someone else your DNA model!
7) Cleanup: You can eat your DNA model or throw it in the trash. Before you eat your edible DNA model, be sure to remove the toothpicks!
A polymer is a large molecule (macromolecule) made up of smaller repeating units called monomers. The DNA polymer is made up of monomers called nucleotides. A nucleotide monomer has three parts: a sugar (deoxyribose), a phosphate group and a base (A, G, C or T). In the model you made, the nucleotide monomer is made up of one squishy candy (the base) plus part of the licorice it is connected to (the sugar and the phosphate).
Did you make wild type or mutant DNA? Remember the pairing rules? For wild type DNA, A pairs with T and C pairs with G. You can see my key in the first picture below. An A-T pair is represented by pink-yellow marshmallows, and a C-G pair is represented by green-orange marshmallows. The middle picture shows a wild type DNA molecule. A is always paired with T and C is always paired with G. The last picture shows a mutant DNA molecule. The third base pair from the top (pink-green) is an A-C pair and the fourth base pair from the top (orange-yellow) is a G-T pair.
Because A-C and G-T are not supposed to pair, they are called mismatched pairs. Mismatched pairs do not fit together as nicely as A-T and C-G pairs do. A better model of my mutant DNA molecule would show a bulge in the "side rail" or sugar - phosphate backbone of the DNA polymer.
DNA sequences contain the instructions for making all the protein molecules in a person, cat, ladybug or any living thing! Let's read the sequence of my DNA polymer. The strand we read is called the coding strand. We will call the left strand the coding strand, and use my colored marshmallow base key above (A = pink, C = green, T = yellow, G = orange). Reading from top to bottom, the sequence is CTAGT.
Can you read the sequence of your DNA polymer?
Click below to download a pdf of the Edible DNA DIY science kit for easier printing.
Make messes, have fun and spread science joy!
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