This is a great introductory activity while introducing the subject of DNA and cellular structure. Cheap, quick, and easy to set up, this activity can leave a lasting impact on students learning. In this lab activity, students will begin to unravel what they will be learning about and conceptualize what it is that they will be learning about. By extracting DNA, students will understand what the substance is, how we can extract it, and many properties of the cell. This hands on activity will help students become motivated to learn more as they take on the role of a farmer, a scientist, a geneticist, and many more perspectives. The flexibility and relatively low cost of this lab experiment makes it a great learning tool.
Step 1: Materials
What you need:
1) Heavy Duty Ziplock Bags or freezer bags
2) Fresh or frozen strawberries, ( can use several other types of food for comparison)
3) 10 mL of DNA extraction fluid (soapy, salty water)
4) 40 mL of ice cold ethanol
5) Test tube/rack
6) Filter and funnel
7) Glass stirring rod
9) 100 mL and 50 mL beakers
10) Microcentrifuge tube (optional)
A cost efficient interchange of materials could be used as well:
Step 2: Introductory Questions
To introduce the experiment, asking questions about DNA and presenting some background information will be useful.
When was DNA discovered?
What is DNA?
What does it look like?
What is the function of DNA?
Where is it found?
Is DNA the same in every cell?
What is DNA analogous to?
Also, explaining background information will be useful in grasping the students attention. Maybe, mention that brilliant minds in the recent centuries, like Charles Darwin, had no knowledge DNA and its function. There are few people alive today that will get a chance to do this experiment.
The most common strawberry, fragaria ananassa, is octoploid meaning that it has 8 sets of chromosomes. This is vastly more DNA that our human cells contain. Also, when ripe the strawberry produces enzymes which help break down the cell walls called pectinases and cellulases. Strawberries are cheap and for the purpose of this lab procedure may be swapped for other fruits like bananas, kiwi, and even foods like a snickers bar.
Step 3: Lab Procedure: Step One
This process is explained and shown by Dr. Green and Carla Easter from the National Human Genome Research Institution.
Step 4: Step 2:
2) Mash the strawberry in the bag without creating too many bubbles for 2 minutes, making sure the consistency is somewhat uniform.
Step 5: Step 3:
3) Measure 10 mL of a buffer solution, which is soapy salty water. ( 5 mL dish washing soap, 5 mL water, pinch of salt) Add the buffer solution into the bag.
Step 6: Step 4:
4) Mash the strawberry again for 1 minute, trying not to make too many bubbles.
Step 7: Step 5:
5) Set up filter and filter the contents into a beaker. Discard the pulp and filter after obtaining the liquid.
Step 8: Step 6:
6) Pour the liquid extract into a test tube so that it is a 1/4 of the way full.
Step 9: Step 7:
7) Obtain 40 mL of ice cold ethanol and slowly pipet the ethanol down the side of the test tube with the extract.
Step 10: Step 8:
8) Wait for the ethanol and extract to form layers, with the ethanol laying above.
Step 11: Step 9:
9) Gently twirl the glass stirring rod just below the ethanol layer and carefully observe the DNA precipitate. Try to spool up as much as possible and carefully remove from the beaker.
Step 12: Conclusions
Ask the students a series of follow up questions that can lead into a variety of other lesson plans.
What did the DNA look like?
How small is DNA and why can we see it now?
Did your opinion change about DNA?
Is DNA the same in every cell?
How was the DNA extracted using Ethanol?
What structures were broken down and how?
Would it be easier or harder to get DNA from humans?
What is DNA's structure, but why does it look like a glob of snot?
What we hold in our hands right now has many implications for our future as scientists. Encourage discussion.