Biology

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Video

Materials

• 1 strawberry
• 1 plastic bag (preferably with a zip lock)
• Isopropyl alcohol (rubbing alcohol)
• 1 drinking glass
• Liquid dish soap
• Salt
• 1 coffe filter
• 1 tablespoon measuring spoon (15 mL)
• 1 teaspoon measuring spoon (5 mL)
• 1 spoon
• Water

Short explanation

DNA is the long filamentous molecule that determines the characteristics of an organism. In this demonstration, you have in a few simple steps succeeded in extracting the DNA of a strawberry. You see it as white, sticky strings.

Long explanation

DNA stands for deoxyribonucleic acid. It's a very, very long molecule which is made up of several small molecules fitted together. DNA looks like a ladder, with steps and sides. However, the ladder is twisted around its own axis.

The order of the small molecules that make up the "steps" is the code that determines the characteristics of an organism. A section of code, that is, a certain number of steps on the ladder, is a gene. A gene contains (somewhat simplified) the code for a certain trait, such as whether you are lactose intolerant or not. All living organisms, human or strawberry, have DNA in their cells. In all organisms, except bacteria and another type of bacteria-like organisms called archaea, the DNA is encapsulated in the nucleus of the cell.

One strawberry is made up of millions of cells. When you mash the strawberry, you spread these cells. In addition, you break the strong cell wall that surrounds each plant cell. The dish soap then dissolves the cell membrane located just inside the cell wall. The contents of the cells now drain, including the cell nucleus. The dish soap also dissolves the membrane surrounding the cell nucleus, and the DNA leaks out. The salt contains ions that attach to the DNA molecules and make them more electrically neutral and thus less water soluble. This causes the DNA molecules to clump together. However, the lumps are too small to see yet.

When you filter the mixture, you remove the large pieces of strawberry that have not been mashed. But it's when you finally add alcohol that the DNA emerges. DNA is even less soluble in alcohol than in water. This causes DNA to accumulate in even larger lumps and become visible to the naked eye.

The DNA you see is DNA from millions of cells. However, it is not pure DNA, but also some other things. Probably the largest component is the proteins (histones) that DNA is wrapped around when it's packed in the cell nucleus. These proteins and DNA are collectively called chromatin, so it may be more accurate to say we are extracting chromatin in this demonstration. However, this is as cool as extracting DNA, because DNA almost always exists as chromatin in nature.

Experiment

You can turn this demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What if you use a kiwi instead? (Psst! It works!)
• What if you use a banana instead? (Psst! It works!)

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