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DNA detective

By Chenxin Tu, 11 May 2023

The DNA becomes solid and forms cloudy clumps.

All living things contain DNA. It’s the stuff that tells cells how to grow and function! In this activity, you can have a go at extracting DNA from fruits around your house.
Safety: This activity involves cutting fruits with a knife and hot water. Ask an adult to help.

You will need

• Soft, fleshy fruit such as peaches, strawberries, kiwi fruit or banana
• Sharp knife
• Zip-lock bag
• Scales
• Dishwashing liquid
• Rubbing alcohol (this is often found in chemists)
• Salt
• Hot water from the tap
• Cold water
• Sieve
• 2 small containers
• Spoon
• Toothpick or skewer

What to do

1. Place the rubbing alcohol into the freezer for 30 minutes.
2. Cut up pieces of fruit and place them into a Zip-lock bag.
3. Squish the fruit inside the Zip-lock bag for about 2 minutes, or until it becomes a mushy mixture.
4. Add 2 grams of salt, 5 grams of dishwashing liquid and 100 millilitres of tap water to a container and mix thoroughly. This is the DNA extraction liquid.
5. Pour all the DNA extraction liquid into the fruit paste Zip-lock bag. Squish the mixture around to make sure they blend nicely.
6. Fill a container half-way with hot water from the tap, and dunk the Zip-lock bag in it. Leave the Zip-lock bag mixture in the water for 15 minutes.
7. After 15 minutes, pour the fruit mixture through a sieve and collect the liquid in a container.
8. Take the rubbing alcohol out of the freezer and slowly pour it on top of the fruit liquid. Leave this for 5 minutes.
9. After 5 minutes, you should begin to see a white cloudy film forming between the fruit liquid and the rubbing alcohol. This is the fruit DNA! You can use a toothpick or skewer to pick up the DNA.

What’s happening?

DNA is the key to life! DNA, which stands for deoxyribonucleic (DEE-oxy-RYE-bo-NEWK-lay-ik) acid, is a long string of chemical parts, and it contains all the information to make a living thing. DNA is stored inside almost all living cells. So the first step in extracting DNA is to rip apart all those cells!

To get DNA from a cell, scientists typically use fancy extraction kits to conduct their experiments. In these experiments, a detergent helps to pop open the cells. This process is called lysis (LIE-sis). In this activity, we made the fruit cells undergo lysis with the dishwashing detergent. Using hot water speeds up this process and helps more fruit cells to burst open and release their DNA into the extraction liquid. Adding salt to the extraction liquid helps tiny DNA strands to clump together, making it easier to separate the DNA from the proteins in the fruit cells.

Many cells contain DNases, which are chemicals that break down DNA. DNases are released if cell walls are broken, which can happen if viruses attack. However, we can slow this process by cooling the solution down. This is why we used the ice-cold rubbing alcohol.

At this stage, there are all kinds of chemicals in our solution – proteins and enzymes and fragments of cell walls. Pretty much all of it will dissolve in rubbing alcohol, but not the DNA. That means the DNA becomes solid and forms cloudy clumps. Now it’s time to investigate if you can extract DNA from other fruits or veggies!

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