Name____________________________________________________ Per_____
Strawberry DNA Extraction
Adapted from Berry Full of DNA by Diane Sweeney for Biology: Exploring Life to be published by Prentice Hall.
Background: Scientists isolate DNA for a variety of reasons, including genetic testing, finding similarities in DNA
of different organisms, for body identification, and analysis of forensic evidence (such as in a crime scene). Today,
we are going to use a method similar to human DNA extraction in order to see DNA from fruit.
A single strand of DNA is extremely tiny, too tiny to see with the naked eye, but because the DNA clumped in this
activity you were able to see just how much of it is found in a strawberry when all of its DNA from its cells is
combined!
For this experiment, we like to use strawberries. But there are lots of other good DNA sources too, such as spinach,
bananas, kiwi fruit, green peas, broccoli.
Each plant cell is surrounded by a protective support structure called the cell wall. We have to crush that by
pounding or blending the fruit. Once we get past the
cell wall, there is a cell membrane made up of a
phospholipid bilayer and proteins. Within the cell is a
nucleus, which also has a membrane similar to the cell
membrane. DNA is found inside the nucleus within
each cell. To see the DNA, we have to break open the
cell membrane and nucleus membrane. We do this
with a mixture of detergent and salt. Why detergent?
Think about why you use soap to wash dishes or your
hands. To remove grease and dirt, right? A cell's
membranes have two layers of lipid (fat) molecules
with proteins going through them. When detergent
comes close to the cell, it captures the lipids and proteins. Why salt? The salt creates an environment where the
DNA will clump together to make it easier to see. After you filter out all of the “chunky” parts, you will add ice cold
alcohol, which will act like a magnet to chemically pull the DNA out of the filtered liquid while the rest of the liquid
remains in solution.
Safety Precautions: Do not eat or drink in the laboratory.
Materials / Equipment (per student group):
1 heavy duty zip-lock baggie
1 strawberry (fresh or frozen and thawed)
1 coffee filter
100 ml beaker or Erlenmeyer flask
1 test tube
1 wooden coffee stirrer or Q-tip (for extracting the DNA out of solution)
10 mL graduated cylinder
Reagents (per class):
 DNA extraction buffer (One liter: mix 100 ml of shampoo (without conditioner) or dish detergent, 15 g
NaCl, 900 ml water OR 50 ml liquid dishwashing detergent, 15 g NaCl and 950 ml water)
 Ice-cold 95% ethanol or 95% isopropyl alcohol
Procedure (make observations for each step with a **):
1.
2.
3.
4.
5.
6.
7.
8.
Place one strawberry in a zip lock baggie.
Smash strawberry with fist for 2 minutes.**
Add 10 ml extraction buffer to the bag.
Mush again (mix it all up really well) for one minute.**
Filter through a funnel into beaker.
Pour filtrate into test tube so that it is 1/8 full.**
Slowly pour the ice-cold alcohol into the tube until the tube is half full.**
At the interface, you will see the DNA precipitate out of solution and float to the top. You may spool the DNA
on your coffee stirrer.**
9. Clean up – rinse funnel, flask, and glass tube. Pour extra strawberry filtrate into a waste container at the front
of the room.
Purpose: To extract DNA from the fruit of a strawberry plant.
Prediction:
What do you predict the DNA will look like? Will you see individual strands? What color do you think it will be?
Answer:
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Observations and Data:
After Step 1, answer this
 Why are you squishing the strawberry
here? In other words, what part of the
strawberry cell are you trying to crush
and why?
After Step 4, answer this
 Describe your observations of the
strawberry. What does it look like after
you smashed it and added the extraction
buffer?
After Step 6, answer this
 Why are you pouring the
strawberry/buffer solution through a
filter?
Answer:
After Step 7, answer this
 Draw an illustration of the tube
containing the strawberry filtrate and
alcohol.
 Be as accurate as possible in your
drawing! Include colors!!
 Identify and label all layers (describe
what is in each layer).
 Be sure to point out which layer shows
the DNA forming!
Answer:
After Step 8, answer this
 Describe what you see as you try to lift
the white precipitate (DNA) out of the
tube.
 What does it look like and what color is
it?
 What does it feel like?
 Is it easy to grab?
Answer:
Answer:
Answer:
Discussion Questions: Answer with complete sentences!
1. Did the DNA look how you expected it to look? How was it similar/different compared to your
prediction?
2. If we looked at the DNA from a different piece of fruit or vegetable, do you think it would look
similar? Explain your answer clearly.
3. Why is it important for scientists to be able to extract DNA from organisms? Give at least two
specific reasons.