DNA From Fruit Smoothies
Instructor
- Place one banana (fresh or frozen) and one pound of frozen strawberries into a pitcher (for edibles).
- Add a little honey and orange juice to approximately double the volume of the fruit (400-500ml).
- Blend for 15-30 seconds with handheld stick blender; just long enough to break up the strawberries. A regular pitcher-type blender does NOT work as well; they are too powerful and will shear the DNA. Add more orange juice if it is too thick. DO NOT OVERBLEND. YOU MAY SHEAR THE DNA.
- Pour into small cups for students.
Students
- Supply each student with a cup of smoothie, one 50ml conical tube (a glass tube is used in these photos for clarity), and one microfuge tube containing approximately 1 ml of liquid dish soap.
- Have your students pour an aliquot of approximately 5ml of fruit smoothie into 50ml conical tube. They may drink the rest!
- Ask your students to add all of their liquid soap to their tube of smoothie, and swirl gently (trying not to create foam/bubbles) for about 3 minutes.
- Have students open their tubes. Walk around the room and tilt each tube at an angle while SLOWLY pouring an equal volume of 95% ethanol (cold ethanol, if possible) down the side of the tube so that it forms a layer on top of the fruit smoothie/detergent mixture. Students should not mix the two layers.
- Students should recap their tubes and observe the gradual appearance over time of DNA at the interface of the two layers, eventually rising to the top of the alcohol layer.
- Students may use a bent hook or wooden stick to try to retrieve the DNA.
Reagents and Equipment Needed
- 1 banana
- 10 strawberries
- 1 ml aliquots of detergent (1/student)
- Paper cups (1/student)
- 50 ml conical tubes (1/student)
- 400-500 ml orange juice
- Handheld stick blender
- Pitcher
- 95% ethanol
- Honey
- Glass hooks or wooden sticks (optional)
Teacher Tips
- Handheld stick blenders are available inexpensively from discount stores (less that $15).
- If 95% ethanol (denatured) is not available, you may use 70% ethanol provided it has been stored in the freezer prior to use.
- Dish detergents should NOT be the antibacterial type – Dawn and Joy both work well.
- Glass hooks can be prepared by bending Pasteur pipets over a flame.
Questions For Students
- Query the students as to the source of the DNA. The smoothie has four ingredients – which of them contains DNA? What experiments could they design to test their hypothesis?
- How could they prove it was DNA they isolated? (Teachers should know that one reason this works so well with strawberries is that a great deal of pectin is co-isolated with the DNA).
|
