I have to admit, even though I’ve been teaching science for 8 years, 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! 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!
- Strawberries/kiwi (at least 2 per group)
- Zip lock bags (one per group)
- 2 tbs dish washing liquid per group
- 2 tbs salt per group
- 1 coffee filter per group (or cheese cloth)
- 1 clear plastic cup (or any other clear glass lab equipment) per group
- ¼ cup cold rubbing alcohol per group
- 1 coffee stirrer per group
- A few extra plastic cups for passing out materials
Rubbing alcohol is a perfectly good substitute for ethanol – like you’d get in the pharmacy section of any grocery store.
Any salt and any dishwashing soap will do!
DNA Extraction Lab Classroom Setup
I split my students into 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 give every student a copy of the 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 read 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 yet.
DNA Extraction Steps
- Give every student a strawberry, or at least 2 strawberries per group. Have the students remove the leaves of their berries.
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. Emphasize that the bag should be passed to each group member and they will get their turn to smush the mixture. Remind the students that they want a very liquid consistency by the end.
While the students are busy smashing away, I like to 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.
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!
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.
Additionally, if you’re interested in my student lab sheet, it’s available for download here.
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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