An Apple a Day:
Extracting DNA from Any Living Thing
Unit:
The Apple Genomics Project
Lesson:
An Apple a Day: Extracting DNA from Any Living Thing
Audience:
This lesson is intended for use with middle and high school science
students. It could also be used with informal audiences, from middle
school age and up, studying DNA, apples, or living things.
General Objective:
To teach youth that DNA is present in all living things.
Specific Objectives:
1. To understand that DNA is present in all living things in quantities
large enough to be seen.
2. To extract DNA from bananas.
3. To make banana smoothies.
Time Required:
About an hour to complete the first part of the project (extracting DNA),
and an additional 15 minutes to complete the second part of the project
(making the smoothies).
Instructor Directions:
Prior to having students complete this project, you should:
1. Make a copy of the project worksheets, enough such that each student has a set.
2. Collect materials needed to complete the project.
Ask students to give examples of living things. Ask students whether the examples they listed
have DNA. Explain that DNA is the “blueprint for life”, containing instructions needed for living
things to develop and grow—so anything living (or previously living) has DNA. Tell students
that this DNA is present in quantities large enough to be seen by the naked eye. Explain to
students that they will extract DNA (e.g. remove it) from banana cells and observe it.
Have students complete the project by following the steps on the project worksheets (included at
the end of this lesson). Assist students when needed, and supervise the making of the smoothies.
Troubleshooting the DNA extraction project:
Problem: No DNA precipitates out of banana/detergent/alcohol solution.
Solution 1: First, check one more time for DNA. Look very closely at the alcohol layer for
tiny bubbles; clumps of DNA are often loosely attached to the bubbles.
Solution 2: If you still do not see DNA, then you need to make sure that you started with
enough DNA in the first place. Many food sources of DNA, such as grapes, also contain a lot
of water. If the blended cell soup is too watery, there will not be enough concentrated DNA
to see. To fix this, go back to the first step and add less water. The cell soup should be
opaque (you should not be able to see through it).
Solution 3: If you still do not see DNA, then you need to make sure that you allow enough
time to pass for each step. Make sure to stir in the detergent for at least five minutes. If the
cell and nuclear membranes are still intact, the DNA will be stuck in the bottom layer. Often,
if you let the banana/detergent/alcohol mixture sit for 30-60 minutes, DNA will precipitate
into the alcohol layer.
Problem: DNA clumps together.
Solution: None. Single molecules of DNA are long and stringy. For example, each cell of
your body contains six feet of DNA, but it's only one-millionth of an inch wide. To fit all of
this DNA into your cells, it needs to be packed efficiently, so DNA twists tightly and clumps
together inside cells. Even when you extract DNA from cells, it still clumps together, though
not as much as it would inside the cell.
After the project has been completed and while students are enjoying the smoothies, ask students
to consider the following questions:
1.
2.
3.
4.
5.
What was the appearance of the DNA?
Is there DNA in your food? How do you know?
Why is DNA essential to all living things?
What do we mean when we say that DNA has been “extracted” from banana cells?
Why do you think it might be important for scientists to be able to remove the DNA
from an organism?
Resources:
Websites:
 For a list of national academic standards met by this activity, see the “An Apple a Day”
lesson on the apple genomics website where you downloaded this activity. The “Apple of
My Eye” lesson also has additional activities and information about apples.
 DNA in My Food? The Making of a Smoothie:
http://www.biotech.iastate.edu/publications/lab_protocols/DNA_Extraction_Smoothie.html
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The Science Behind Our Food: Lesson in a Trunk: Banana DNA Extraction:
http://devacaf.caes.uga.edu/main/index.cfm?page=liatpics&trunkName=Banana%20DNA%20Extraction
Genetic Science Learning Center at the Eccles Institute of Human Genetics at the
University of Utah: http://gslc.genetics.utah.edu/units/activities/extraction/
Books:
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DNA Is Here to Stay. Dr. Fran Balkwill. 1992. ISBN # 0-00-191165-1. (Ages 9-15)
Amazing Schemes within Your Genes. Dr. Fran Balkwill. 1994. ISBN # 0876146353. (Ages 9-12)
Double-Talking Helix Blues. Joel Herskowitz. 1993. Book/cassette tape. ISBN # 0-87969-431-9. (Ages 4-8)
Ingenious Genes. Patrick A. Baeuerle and Norbert Landa. 1998. Barron's Educational Series, Inc.,
Hauppauge, NY. ISBN # 0-7641-5063-4. (Ages 9-12)
Name: ___________________________________
An Apple a Day: DNA Extraction
In this project, you will extract DNA from banana cells. You will then treat a portion of the
banana mixture with detergent, salt, and cold alcohol to precipitate the DNA from the banana
solution.
Materials Needed
Blender
Two 5-ounce plastic cups
Plastic spoon
Graduated cylinder*
#2 cone coffee filters
Distilled or tap water
Dawn dish detergent**
2 peeled bananas
Teaspoon
2 pinches of table salt (iodized or noniodized)
Plastic transfer pipette or medicine dropper
Two test tubes, with caps
Test tube stand
95% ethyl alcohol***
Ice and ice bucket
Glass rod****
Post-laboratory worksheet
*Or liquid measuring cup and dry measuring spoons
** Or Suave clarifying shampoo
*** Or 91% isopropyl alcohol
****Or wooden stick, or glass Pasteur pipette modified into a hook
Procedure
Carefully read and follow the directions. Place a checkmark next to each step as you complete it.
1. Obtain an ice bucket and fill it with ice.
2. Place about 5 mL ethanol (or isopropyl alcohol) into one test tube, cap the test tube,
and place it (upright) into the ice bucket. You’ll need to use ice-cold alcohol to get
the best results for this exercise.
3. Add two peeled bananas and one cup (about 250 mL) distilled water to a blender.
Blend for 15-20 seconds, until the solution is a mixture. (The instructor may have
already performed this step, so check first.)
4. In one of the 5 oz. plastic cups, make a solution of one teaspoon of Dawn
dishwashing detergent and two pinches of table salt. Add 4 teaspoons (about 20 mL)
of distilled water or until the cup is about one-third full. Dissolve the salt and
shampoo by stirring slowly with the plastic spoon to avoid foaming.
5. Add three heaping teaspoons (about 15-20 mL) of the banana mixture from step three
to the solution from step 4. Slowly stir the solution with the plastic spoon for 5-10
minutes. (The detergent dissolves the lipids that hold the cell membranes together,
thus releasing the DNA into solution. The detergent causes lipids and proteins to
precipitate out of the solution, leaving the DNA. The salt enables the DNA strands to
come together.)
6. Place a #2 coffee filter inside of the remaining 5 oz. plastic cup. Fold the coffee
filter’s edge around the cup so that the filter does not touch the bottom of the cup.
7. Pour the mixture from step 5 into the filter. Let the solution drain for several minutes
until there is approximately 5 ml (covers the bottom of the cup) of the filtrate, from
which the DNA will be extracted.
8. Fill the plastic pipette with solution from step 7 and transfer it to the remaining test
tube.
9. Remove the test tube of cold alcohol from the ice bucket. For best results, the alcohol
should be as cold as possible.
10. Tilt the test tube containing the filtrate to one side. Slowly pour the alcohol into the
filtrate down the side, so it forms a layer on top of the banana filtrate. Pour until you
have about the same amount of alcohol in the tube as filtrate. Alcohol is less dense
than water, so it will float on top of the banana solution.
11. Let the column sit for 2-3 minutes without disturbing it. It is important not to shake
the tube during this time, because the strands of DNA are fragile at this point.
DNA is not soluble in alcohol. When alcohol is added to the mixture, the components
of the mixture, except for DNA, stay in solution while the DNA precipitates out into
the alcohol layer.
12. You can watch the white DNA precipitate out of solution into the alcohol layer. DNA
has the appearance of white, stringy mucus. The protein and grease parts from the
banana cells stay in the bottom, watery layer of banana filtrate, while the DNA
precipitates into the top layer of alcohol. Look for DNA at the point where the alcohol
layer touches the filtrate layer, since this is where the DNA will precipitate first.
13. When good results are obtained, there will be enough DNA to spool on to a glass rod.
Or, you can retrieve some of the DNA by using a wood stick or a Pasteur pipette that
has been heated at the tip to form a hook. Once the DNA has risen into the alcohol
layer from the banana layer, the DNA will be a long, stringy molecule that clumps
together.
14. Congratulations! You have just extracted DNA! Now, answer the questions on your
post-laboratory worksheet. Clean up your workspace according to your instructor’s
directions.
Name: ___________________________________
An Apple a Day: DNA Extraction, Part 2
Make a Smoothie
With permission from your instructor, after you finish your extraction activity you may follow
the recipe below to make a banana-strawberry smoothie:
1. To the remaining banana mixture in the blender, add the following ingredients and blend
until smooth.
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An additional peeled banana, cut into pieces
One 10-ounce package of frozen strawberries, partially thawed
One 12.3-ounce package of tofu (either soft or firm, cut into pieces)
One cup orange juice (add more for a thinner consistency)
Two tablespoons of honey (or more, to taste)
2. Share the smoothie with your classmates in 5 oz. cups. This recipe makes enough for 10-5
oz. cups.
3. Evaluate your smoothie. Why do you think the tofu is in the smoothie?
Name: ___________________________________
An Apple a Day: Post-laboratory Worksheet
Results:
Describe the suspension in the tube.
Draw and label the ethanol suspension.
Analysis and Conclusions
1. Describe the appearance of the DNA.
2. What was the purpose of the salt solution used in the beginning step?
3. When you do dishes at home, what happens when you put dish soap in a bowl or
pan with a lot of grease (fat) in it?
4. Why, then, was the detergent added to the banana mixture?
5. Why do you think it might be important for scientists to be able to remove the DNA from an
organism?
6. Is there DNA in your food? ___________ How do you know?