Friday, July 22, 2011

Home Science and DNA Extraction

Kat and I love to look at things under the microscope. We bought one for Kat's fourth birthday, and have been in love with it ever since. At first we looked at the standard prepared slides: the flea, the bee wing, and the pollen spore. This entertained us for about five minutes before we looked elsewhere for anything we could find to put under the microscope. We looked at red blood cells (from my finger), water from the sink, juice, insects, hair, anything we could think of. We watched as Carl Sagan explored the inner life of the cell and we marveled at the small universe contained within our own bodies.

Along with skin cells, red blood cells are some of the easiest cells to look at under a microscope. 

In the years that have followed that fateful purchase, our microscope has faced the wear and tear of people who have learned how to use it, and have grown to love it. I have brought it outside with us, so that we may engage others in learning about cells and the smaller world around us. In fact, the first time we did this, I found myself explaining to a group of 8 year old kids that the cells inside our bodies are kind of like legos or building blocks. There are trillions of them inside our bodies, and it takes billions of them to clump together to build things like our heart, brains, and lungs. Every single living thing is made up of these tiny things called cells, and although they are incredibly small, we can use something like this microscope to see them! The looks of wonder and delight on their faces was incredibly rewarding, but even more so was the fact that like us, they all scampered off looking for more things to look at under the microscope.

As we continued learning about our smaller world, we wanted to go deeper. We wanted to see the inner structure of the cells, we wanted to see an endoplasmic reticulum, some mitochondria, or even the nucleus. That's when I came across this D.N.A. Extraction Demonstration. This is a really fun and really simple way to extract the DNA and the proteins that bind them out of regular old strawberries. Now we had a way to actually see some of the cell components that we had been talking about!

Most of the items for the experiment can be already found in your home.

Materials Needed

200 mL 91% isopropyl alcohol (you can find 91% at any drug store, put it in the freezer for later)
1 empty 1 L bottle
100 mL liquid dish soap
2 tsp salt
Stirring rod or spoon
Plastic bag


1. Put your strawberries into the plastic bag. We used 6 or 7 strawberries. Mash them up for approximately two minutes, or until they begin to foam. You want them to have a consistency like jam. Set aside when finished.

Kat had a lot of fun squishing these strawberries!

2. Take your empty bottle and add the liquid dish soap and salt, fill it the rest of the way with water. Put the cap on and gently turn it upside down a few times to stir everything together.

One of the things that I love about this experiment is that I can let my daughter conduct it herself!

3. Take your bag of strawberries, open it, and add the extraction solution. I added about 150 mL to the strawberries, but the general idea is that you want to double the volume in the bag. Close the bag, and shake it again to mix everything together.

4. Place the sieve over a bowl, and pour the contents of the bag into it. Once the liquid drains into the bowl, set the sieve aside. Take 200 mL of your chilled rubbing alcohol and slowly pour it into the bowl. Do not mix it.

Pour slowly, you don't want things to splash around and mix the layers of liquid.

5. Observe what happens in the bowl. After approximately one minute, you should begin to notice some milky white strands appearing near the top of the bowl. Once they start congealing together, use your stirring rod or spoon to twirl it. You will be surprised to find that it is nearly a solid mixture of proteins and D.N.A.! The broken cells of the strawberries are left at the bottom of the bowl, while the D.N.A. rose to the top of the alcohol.

You will quickly see the strands of D.N.A. pull together and rise to the top.

6. To make this demonstration an actual experiment, try the same process with different types of foods. Will you get the same effect with blueberries? What about bread? What will happen if you leave the salt out of the extraction mixture? What would happen if you put the D.N.A. in the freezer?

You can actually play with the "building blocks of life"! How cool is that?!

We experimented with different kinds of fruits and found that certain kinds gave us the best yields in D.N.A. and proteins. We expected that other kinds of fruits (such as blueberries) would give us better results, and we were surprised with the conclusion we made (no spoilers, I want you to try this for yourself!). We also looked at the cells of the strawberries under our microscope at each stage and were surprised with what we found. We were able to see the cells as they broke apart with the extraction mixture, and then small globules as the D.N.A was bound with the alcohol and salts.

This was one of the coolest experiments that we had conducted, as it allowed us to see some of the smaller elements of cells without requiring the use of a high powered electron microscope. This is something that is really easy to do with your kids, and it allows something that used to be somewhat of an abstract concept, to be a physical reality that they can actual play with.

Still, if technology ever allows small, personal electron microscopes to enter the marketplace at an affordable price, you better believe I will be clamoring at the door to get one!


  1. I love it. I'll never use Trizol or spin columns again.

  2. The sweet little helper pictured above should be wearing eye protection to keep those peeper safe.

    1. You are correct! Lab safety is very important. Since then, we have bought a few pairs of safety goggles, and keep them near our lab area. :)