What’s the point?
To see DNA.
How do you do it?
What do you need/What do you do?
½ of a banana
1 drop of dish soap
tiny pinch of salt
3-4 Tbsp water
Isopropyl alcohol is flammable and can be a fire risk, so keep it away from any flames or sources of ignition. It is also toxic if ingested. Wear appropriate protection.
Since DNA is the blueprint for life, everything living contains DNA. Our source of DNA is a banana. The detergent and the mechanical ‘mashing’, break down the banana cell walls, plasma membranes and nuclear membranes to release the DNA. The detergent emulsifies the lipid bi-layer of the membranes. We wash our hands with soap to destroy bacteria/germ cells. DNA has a net negative charge. The sodium ions of salt (NaCl) neutralize/shield and stabilize the DNA molecules, allowing them to move closer together. The alcohol dehydrates the DNA so that it precipitates out of solution. This happens at the interface between the banana liquid and the alcohol. The protein and grease that we broke up in the first step prefer the bottom, watery layer, while the DNA prefers the top, alcohol layer. DNA is a long, stringy molecule that likes to clump together.
Imagine this: the human body contains about 100 trillion cells, each of which contains six feet of DNA. If you do the math, you'll find that our bodies contain more than a billion miles of DNA!
Note: Ice-cold alcohol works best but you can also use alcohol at room temperature.
Experiment with other DNA sources. Which source gives you the most
DNA? How can you compare them?
Experiment with different soaps and detergents. Do powdered soaps
work as well as liquid detergents?
Experiment with leaving out or changing steps. Try changing how
much of each ingredient you use.
Learning Center @ The University of Utah (2005)
Modified from Bilash, B.
& M. Shields. A Demo a Day: A
Year of Biological Demostrations. Flinn Scientific., Inc. Batavia, Il.
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