Wednesday, July 23, 2014

Sweet Science: Strawberry DNA Extraction Lab!

Science at the park! A DNA Extraction lab on a crisp fall day.
Photo Credit: Alex Gregory, ASU Photojournalism student

One of our favorite biology labs to do is the DNA Extraction Lab. We've been doing this activity since my daughter was 4 years old, and it is a fantastic and fun way to get a closer look at the tiny world inside of us!

DNA exists inside of every single cell in our bodies, as well as every living cellular organism (that we know of) on Earth. You can think of DNA as the "code" that lets our cells know what job they have, and what category of tissues they belong to. Some cells are coded to be a part of our eyes, while others are coded to be a part of our muscle tissue. Every cell is encoded with DNA, even red blood cells, bacteria cells, and skin cells! 

DNA is one of the most important foundations of life on Earth, but it's so small, it's impossible to see! It's also locked in tight within the cell's nucleus, protected against contamination and corruption. However, there is a way where you and your kids can isolate the DNA out of cells, extract it, and see it for yourselves!

Photo Credit: Alex Gregory, ASU Photojournalism student

Note: For our day of science in the park, we made a HUGE batch of strawberry DNA. For results in the photos, multiply the ingredients by 5!

Materials Needed:

1. 2 Strawberries (bigger is better!)
2. 180 ml (2/3 cup) of water
3. 15 ml (1 Tbsp) of liquid dish soap
4. 2 g (2 Tbsp) salt
5. 10 ml (2 Tbsp) cold 91% isopropyl (rubbing) alcohol
6. Strainer
7. Cup
8. Fork
9. Ziplock bag
10. Safety Goggles

Note: The night before you do your lab, put your bottle of isopropyl alcohol in the freezer. While it won't freeze, the colder the alcohol gets, the better the DNA extraction works. 


1. Put on your safety goggles!

2. Combine your water, salt, and dish soap in a cup. Gently stir to thoroughly mix the ingredients.

3. Put your strawberries in a plastic bag. If they are frozen strawberries, make sure to thaw them first!

4. Add your salt, water, and dish soap to the bag. Close the bag, and make it as air tight as possible.

Photo Credit: Alex Gregory, ASU Photojournalism student

Here's the fun part - MASH YOUR STRAWBERRIES!!! Mash them with gusto! Keep mashing them with until they become foamy and everything has blended together into a pulpy liquid.

6. Put your strainer over your cup and carefully pour your strawberry mixture through the strainer. You can use your fork to press down on the strawberries, getting as much pulpy liquid into the cup as possible.

Photo Credit: Alex Gregory, ASU Photojournalism student

Slowly pour your cold isopropyl alcohol into your strawberry liquid. Wait approximately 2 minutes.
You should begin to see some white strands form over the top of your mixture. This is DNA!

8. Take your fork and slowly skim the surface of your liquid. You'll be able to pull out a large clump of pink and white material. This gooey substance is strands of DNA mixed with the broken proteins that held it all together!

Photo Credit: Alex Gregory, ASU Photojournalism student

While you still won't be able to see the double helices themselves, you can see the long strands that contain them! Take a small sample of your strawberry DNA and put it on a glass slide, with a slip cover on top. Put it under your microscope and take a look! That's DNA!

Photo Credit: Alex Gregory, ASU Photojournalism student
How It Works:

So how did this all come together, anyway? Well, using strawberries is actually really important for this lab! Commercially grown strawberries are known as "octoploids", meaning they contain 8 pairs of chromosomes! By comparison, humans have 2 pairs per cell. They also contain special enzymes (pectinases and cellulases) that help break down the cell walls. So, while any fruit will work, commercially grown strawberries will give you a much better yield of DNA!

Now let's get into the mixtures we used. The soap helps break down the thick cell walls of the strawberries. The salt (sodium chloride) helps break apart the protein chains that are bound to the DNA. It also helps keep them dissolved within the water, so they don't reattach themselves to the DNA strands. When you mash the strawberries, you're really working to break apart those cells and get that DNA out of there!

The alcohol plays a very important role in this lab. DNA is not soluble in alcohol, which means that it won't dissolve. The colder the alcohol is, the better this works, which is why it's important to stick it in the freezer the night before (in a closed container please!). The alcohol is also less dense than water, so it will automatically rise to the surface, carrying the DNA with it!

There are other DNA extraction labs that you can conduct in your home. You can collect a sample of your own DNA by swabbing your cheek cells! Here is a link to a great tutorial for a cheek cell lab.

You can also make your own jewelry with DNA! Just take a small microcentrifuge tube, and put your DNA in there. You can tie string to it, make a beaded necklace, or you can make a bracelet or earrings with it!

Here's a print out of our strawberry DNA extraction Lab. Just right click, save, and print!

Image Credit: Amy and Kat Oyler

We'll be taking our DNA extraction lab to the kids at our local library, where they'll not only get to extract strawberry DNA, but they'll also get to make their own jewelry with it! It's such a fun and easy way to get a closer look at the biological wonders around (and within!) us. I can't wait to share this with the kids in our community!

If you're in the Phoenix area and would like to come extract DNA with us, here's the info! You can also find it listed with The Arizona SciTech Festival!

What: Strawberry DNA Extraction Lab and Jewelry Making!
Where: Burton Barr Library (the big downtown library on Central and McDowell!)
When: Tuesday, July 29th, from 2-4pm.
Who: The Scientific Mom, MACH1's Terry Ann Lawler, and The Scientific Kat!
Why: Because science is AWESOME!

A happy end to a wonderful day!
Photo Credit: Alex Gregory, ASU Photojournalism student

Happy Exploring!

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