A Look Inside: DNA Extraction

The wonder of DNA - it controls everything your body does and how it looks. You can’t see it without a microscope…or maybe you can!  DNA fills every cell in our body. We can’t even see individual cells without a microscope but this lab allows you to extract DNA from cells, get it to clump together so that you can see it without a microscope.  Of course you will not see the famous double helix structure but students are always amazed with this experience!

I have used this format for Open Sci Ed 8.5 Genetics, the Junior Girl Scout Detective badge and the Cadette Special Agent Badge.

Material Notes - 

• Small plastic cup

• Large plastic cup

• Coffee filters

• Large popsicle stick

• Coffee stirrer or other small straw

• Salt

• Soap

• Water

• Graduated cylinder (or other measuring instrument)

• Ziplock bag 

• Strawberry (I used defrosted strawberries, I have seen kiwi and banana also be successful)

• 91% isopropyl alcohol - store in the FREEZER and take out right before needed

I make trays for students with all of the items.  Often I will leave the coffee filter off because if it gets wet before it is needed in the experiment it is a problem.  Here is a general set up of the materials.

Introducing the Lesson - 

One of the strategies that I use with students when going through a procedure is to give them a handout of all the steps but leave blanks.  As I go through the steps with them and model some of the steps, they have to fill in the blanks to help keep them on track and focused.  Here is the procedure sheet with a key.

Procedure - 

This follows the procedure in the link above.  I will add a few additional hints and notes that will help you and your students to be successful.

• Step 1: Squish the strawberries in the zip lock bag but don’t hurt the bag.  More things will be added to the bag throughout the lab so it is important that the bag stay intact without holes or tears.

• Step 2: Measure 10 ml of water and place it in the small plastic cup. For those of you that do not have graduated cylinder or are doing this in a non science setting 10ml is about 2 teaspoons.

• Step 3: Use the popsicle stick to add a pea-sized amount of salt to the water in the cup.

• Step 4: Use the coffee stirrer to add a little soap to the cup with the water and salt.

• Step 5: Use the coffee stirrer to gently dissolve the salt, but not too crazy because you don’t want a lot of bubbles.  Some bubbles will most definitely appear. We just want to avoid having large bubbles or the bubbles taking up the majority of the cup.

• Step 6: Open the ziplock bag and pour the water/soap/salt mixture into the bag with the strawberries.  Seal the bag! Make sure the bag is sealed.  Mush the mixture together.

• Step 7: Place a coffee filter over the page cup.  Pour the strawberry mush mixture into the coffee filter and allow to drain.  After about one minute gently squeeze the coffee filter to release any additional liquid.  THROW THE COFFEE FILTER AND ZIPLOCK BAG AWAY!   If the coffee filter rips, get a new one and place it over a new cup.  Pour from the original large cup to refilter.

• Step 8: Go to one of the stations with ice cole rubbing alcohol. Fill the pipette and carefully release the rubbing alcohol so it runs down the side of the cup. Repeat one or two more times for a total of 2 or 3 pipettes of rubbing alcohol.  Store the alcohol in the freezer.  I set up a few stations that has a cup of cold alcohol and a 1 ml disposable pipette, as opposed to having it on the student trays.

• Step 9: Carefully return your cup to your table.  Use the coffee stirrer to lift the white, goopy fibers that have formed where the rubbing alcohol meets the strawberries - that is DNA! 

• Step 10: Clean the cups and straighten your tray so that it looks the same as when you received it.  Cups are reusable from class to class if needed.