At the end of this tutorial you’ll find links to a free, student-friendly presentation (with pictures) to walk your class through this DNA Extraction Lab one step at a time. You’ll also find a free download for a student lab sheet.
I’ve been teaching life science for 8 years, and I’ve always found (to my dismay) that students have a hard time connecting with the miracle of DNA. This molecule carries instructions for all life, and it’s self replicating! Small changes in this molecule are the reason that we have the varieties of life on Earth that we have. Don’t let your genetics unit just be diagrams in a text book. You owe it to your students to bring this molecule to life. Let them get their hands dirty and touch science. Use this lab as phenomena to pique interest before diving into content.
I have to admit, at first I was scared of the DNA Extraction Lab. I knew it was simple; I’ve done the process myself. Rather, I concerned about classroom management and where I’d find all the materials. I had nightmares the night before as I envisioned my classroom going crazy. All for nothing, it turns out. This lab is simple and easy to implement! Best of all, it’s cheap! I’ve prepared this step by step guide for you so that you can bring the joy of hands on science to your classroom too!
Rubbing alcohol is a perfectly good substitute for ethanol – like you’d get in the pharmacy section of any grocery store.
Salt and dishwashing soap. Any brand will do.
I split my students into table groups of 3 and 4 for this lab. To keep everyone engaged, I make sure each student got their very own strawberry to smush. I also give every student a copy of this FREE DNA Extraction Lab Student Sheet also. Everyone is required to complete and submit the lab sheet upon completion of the lab.
If you’re using my lab sheet, I like to begin by reading the included page on the history of DNA and the reasons for each step of the extraction process. This is a great extension if you’ve taught Cells or the Cell Theory already.
When you’ve got everyone and their strawberries ready, begin the lab. Remember, you can also use my presentation (linked at the end of this tutorial) to keep students on task during the process.
2. Pass out a zip lock bag to each group. Set a timer (I like 5 minutes for this step.) for the time each group will have to smush their strawberries. Each student will add their strawberry to the group bag and take their turn smushing. Emphasize that the bag should be passed to each group member and that everyone will get a turn. Remind the students that they want a very liquid consistency by the end.
While the students are busy smashing away, I prepare the mixture for the next step. I make a small cup with salt (a couple tablespoons), dish soap (a tablespoon or so), and maybe a third or fourth a cup of water for each group. Exact measurements are not a concern.
Before you move on, student bags should look like this:
The mixture you’ll prepare (soap, salt, and water) should look like this:
3. Pass out the cups filled with DNA Extraction Liquid. Have the students pour the whole cup full into their zip locks and then smash the mix up a little bit more.
As students do this, I pass out one clear cup to each group and a coffee filter.
4. Students will now strain their strawberry mix through a coffee filter (or cheese cloth) to remove the solid pieces. They’ll need to have one student hold the filter and cup while another student pours.
Students may want to really wring out the mix. That’s a great idea! Get as much liquid as you can from the strawberry mix! Some students broke their filter and I had to give them a new one and let them begin again. This is important because you really don’t want chunks left in the final cup. It should just be red, soapy strawberry juice.
While students complete this step (which tends to be a very messy and exciting one), prepare cups with a fourth or third cup of cold ethanol or rubbing alcohol.
5. Pass out the cups of rubbing alcohol and instruct students to carefully pour them into their clear cup of strawberry liquid. They should pour down the side of the cup not directly into the mix so that they do not damage the DNA.
6. At this time, students can throw away and clean everything except the clear cup of strawberry liquid. I like to nominate one student to wash all the ingredient cups so that they can be re-used.
It takes just a few minutes for the DNA to precipitate from the mix.
7. Using a coffee stirrer, allow students to remove the DNA from their cup to touch and examine!
To help you in the classroom, I’ve created a version of this process on Google Slides that you can display on the board as you go through the lab.
Click here to download the free step by step presentation.
Download the student lab sheet by clicking below.
Finally, if you’d like to learn more about how I teach my DNA Unit, check out this blog post for a teacher’s guide!
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