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James P. Allison, 2018’s Nobel Prize recipient in Physiology or Medicine for his research in cancer immunotherapy, observed that a protein in our T cells was giving cancer cells a break. He set out to teach those proteins how to block cancerous cells from going crazy. He succeed, in mice, where T-cells finally cured the cancer.
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2011 was the Year of Science in British Columbia, Canada. On April 10, a science fair was held at the Civic Center in the City of Prince George. The stall that attracted me the most, among many, was one instructing visitors to extract DNA from several available fruits: strawberries, bananas, kiwi, and nectarines. (The reason I was most attracted to this stall probably stems from a childhood desire to study medicine or some stream related particularly to Genetics…)
I was eager to see the DNA strands pop out of fruits and I decided to conduct the simple experiment. I took half a Californian strawberry, carefully smashed it in a Ziploc, mixed it with saline water and some specific kind of alcohol, to eventually collect the chromosome strands from the solution and store it in a take-away test tube, which I conserve to this day.
In this article, I present the simple steps you could follow to extract DNA using merely household materials. These steps are taken verbatim from a leaflet printed by Genome British Columbia I picked up at the fair.
DNA Extraction Experiment
- Kiwi (or strawberry or banana)
- Table salt
- Bottled water
- Clear cup
- Spoon or straw
- Tape or elastic band
- Liquid dish detergent
- Cheesecloth (3 layers)
- Cold isopropanol (can be purchased at a drugstore, should be placed in the fridge to cool)
- Wooden or glass stir stick (I used wooden stick to stir the mixture, as explained below)
- Make the buffer solution by mixing 1 tsp of table salt in 100 mL water. (Note: the salt solution will help precipitate proteins and carbohydrates away from the DNA.)
- Make the soap solution by mixing 3 mL (3/4 tsp) liquid soap with 27 mL (2 tbs) water.
Steps to follow
- Scoop out the fruit flesh into a sandwich wrap and mash well for 2 minutes. (Note: mashing helps break apart the cells and loosen the tough cell wall. If using kiwi, peel the skin, since the skin comprises relatively dead cells, which can’t produce much DNA.)
- Add 10 mL of buffer solution and grind for at least 5 minutes. Use your strength to really mash it up!
- Assemble the filter by covering the top of a cup with the three layers of cheese cloth. Tape the cheese cloth around the cup.
- Pour the fruit mash through the filter. Let the solution drip into the cup.n
- You can get extra juice by squeezing the mixture in the cheese cloth through the cloth.
- Add 3 mL of the soap solution to the filtered liquid. Swirl gently to mix. (Note: the soap will break open the cellular and nuclear membrane so as to release the DNA.)
- Pour 2 volumes of the cold isopropanol down the length of a straw (or the back of a spoon) into the fruit liquid.n
- The isopropanol needs to form a layer on top of the kiwi liquid. (Note: 2 volumes means twice the amount of the fruit liquid.)
- Let the liquid sit for a while. The DNA should precipitate where the fruit liquid meets the alcohol. You can use the wooden stir stick to spool some out of the cup! There you go!
And that’s what I did as well. In the following photo you can see my small test tube containing my California strawberry DNA in some alcohol solution:n
Needless to say, don’t hesitate to try the DNA experiment at home — it’s really fun and instructive!
One final remark: Interestingly enough, people using bananas rather than kiwi or strawberries, collected a far larger amount of DNA. I asked a geneticist friend of mine for the reason, and he said that the bananas were probably not organically grown. Non-organically-grown fruits tend to have larger-sized chromosomes, hence producing more DNA upon extraction.