A Gene-ius Activity from Science Buddies
Ever wondered how DNA, the genetic blueprint of a life-form, can encode and pass on the information on how to grow and maintain that life-form? Just like a cookbook contains a recipe for a dish, DNA stores the recipe for the life of an organism. Unlike various recipes, however, very different organisms’ DNA such as in a fungus, plant or animal all look very similar. Although each human has a unique DNA sequence, the DNA in all of us is about 99.9 percent identical! In this activity you will make a model for a short section of DNA—enough to get a sense of what it is like and how it encodes life.
Plants, fungi and animals might seem very different from one another but they are all made up of tiny building blocks called cells, and—with very few exceptions—each of these cells has in its center a molecule containing the organism’s blueprint. This molecule is called DNA: deoxyribonucleic acid. Although the blueprints differ across life-forms—after all, plants, fungi and animals are very different organisms—the way it is encoded in DNA is identical.
The DNA molecule encodes all information using four chemical bases: cytosine (C), guanine (G), adenine (A) and thymine (T). It has two complementary strands, each with a long sugar–phosphate backbone to which the four chemicals attach. The sequence or order of these chemicals contains the data to develop, maintain and grow the organism. In DNA these four chemicals always link together the same way to form pairs: A pairs with T; C pairs with G. In this very specific way the two complementary strands link together to form DNA: a long molecule that looks a little like a rope ladder—only about 200,000,000 times smaller! Give the “ladder” a clockwise twist, and you can see why DNA is also called the “double helix.”
When organisms grow, their cells divide and in almost all cases each cell receives a duplicate of the DNA molecule. DNA’s ingenious structure allows for easy replication: Each strand of the double helix contains all the information needed to create a new DNA molecule. If the pairs let go of each other, each backbone with its sequence of four chemicals can be the bases of a new DNA molecule. As A and T always pair up and C and G also always go together, one strand is enough to re-create the molecule.
Observations and results
You were most likely able to tell what the hidden colors were—no matter which strand you chose to hide. This is because once you know one side of a pair you know its partner, because these chemicals always pair with the same partner: red with blue; green with yellow.
The four code chemicals in real DNA are usually represented by the letters T, A, C and G. They are not colorful, but they are as particular: T and A always pair together, as do G and C. The sequence along one backbone of the DNA molecule contains all the information to re-create the molecule.
You probably have about 30 base pairs in your model. You would need to make it 100 million times longer to model all three billion base pairs of human DNA. Your model would be about 60,000 kilometers, or 37,300 miles, long—about 1.5 times around the world! Your DNA molecule is probably about four centimeters wide. Real DNA is about two nanometers, or two millionths of a millimeter wide. This means your model is about 20 million times wider than real DNA. This long string of DNA is coiled and folded into the center of almost every cell of the human body!
More to explore
DNA: Definition, Structure and Discovery, from LiveScience
Find the DNA in a Banana, from Scientific American
Squishy Science: Extract DNA from Smashed Strawberries, from Scientific American
Identical Twins Genes Are Not Identical, from Scientific American
Science Activities for All Ages!, from Science Buddies
This activity brought to you in partnership with Science Buddies