1. science
2. medicine
3. genetics

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DNA Extraction Lab Activity
Purpose: As you have already learned, all living things contain DNA and protein in their chromosomes. In the
plant world, many fruits have more than the usual two sets (pairs) of chromosomes. Every cell in a strawberry contains
eight copies of each of its chromosomes. As a result, strawberries contain large amounts of DNA. This makes
strawberries an ideal source of DNA. Strawberry DNA is easy to extract because strawberries are easy to mash, and
ripe strawberries produce enzym es that contribute to the breakdown of cell walls. To extract the DNA, you will
first break strawberry cells apart mechanically, by crushing them. Next, you will add detergents to dissolve the cell
membranes (plasma membranes). You will then filter your solution to remove cell organelles, broken cell walls,
membrane fragments, and other cell debris. The resulting red colored solution contains DNA and other small
dissolved molecules such as sugars and proteins. When cold ethanol, a type of alcohol, is layered on top of this
solution, molecules of the alcohol repel the DNA molecules, and the DNA clumps together. Each clump contains
many, many DNA molecules and is large enough to see with the unaided eye. You will work on an inquiry to
determine what variable would affect the extraction of DNA: type of fruit (compare strawberry to banana and kiwi),
concentration of detergent, types of detergent solution (laundry, hand-soap, and dish soap), concentration of ethanol,
time strawberry is mixed with detergent solution, etc.
Problem: (Develop a problem questions you would like to investigate in relation to DNA extraction. Look at the
materials and the procedures, would you like to investigate what fruit gives the most DNA, does cold ethanol make a
difference, what is the best type of detergent to use, and does the time mashing matter?)
H ypothesis: (Form and record a hypothesis to answer problem. If … then… because…)
Pre-Lab Q uestions:
1. If a molecule of DNA is invisible even under a microscope, how will you be able to see the strawberry DNA you
extract? How does strawberry DNA appear to the human eye?
2. To isolate strawberry DNA, you must separate it from other cell materials. Some of the lab steps you will use are
listed below. Match the letter of each lab step with its effects on strawberry cells and enter your answers in the
spaces provided.
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M aterials: heavy duty zip lock baggie, 1 fruit (ripe), 10 mL DNA extraction buffer (detergent solution – ex: laundry,
dish, hand soap), coffee filter, funnel, small beaker, ethanol solution, distilled/deionized water, clear test tube, glass
rod, weigh boat
Safety Precautions: chemical safety, glassware safety, eye safety, clothing protection.
M ethodology: Read each step before writing your
procedures.
For each of your trials you need to complete the following:
1.
2.
Place one _____________(fruit) in a self closing plastic bag.
Press the air out of the bag and seal it carefully.
3.
Mash the bagged _______________(fruit) for 2 minutes.
4.
5.
Add 10 mL of _______________detergent solution to bag.
Press the air out carefully and seal bag.
6.
7.
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Mash the bagged fruit for ____ minute.
Set up your filtration apparatus as shown.
Place the test tube securely in the beaker.
Slowly pour the liquid extract into the filtration apparatus.
Let it drip directly into the test tube.
When the test tube is about 1/8 full, remove the funnel.
Discard any extra mashed fruit pulp with filter paper.
13. Slowly drizzle _____________ethanol along the side of the test tube, until the test tube is about half full of
liquid. The ethanol should form a separate layer on top of the filtered extract.
14. Dip the glass rod into the tube to where the alcohol and extract layers meet.
15. Gently twirl the loop or rod while keeping the tube at eye level so that you can see what is happening.
16. Observe the characteristics of the DNA as it precipitates (clumps together).
17. Record the mass of DNA. Record volume of DNA.
18. REPEAT WITH TWO MORE FRUIT.
Data and O bservations:
! Create a diagram of observations. A labeled drawing and qualitative description of results.
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! Data Table: (Columns: type of fruit, types of detergent solution, temperature of ethanol, time fruit is mixed
with detergent solution, Mass of DNA, Volume of DNA)
Type of fruit
Type of
Temperature of Time fruit
M ass of DNA Volume of
detergent
ethanol
M ixed
DNA
Conclusion:
! Summary of Results
o Describe your results.
o Identify the independent variable, the dependent variable and the control.
o What did the DNA look like? Be sure to include color, shape, texture, odor and other observations.
" Relate its chemical structure to how it looks when lots of it is clumped together.
o Was your hypothesis correct?
o How could this experiment been done differently?
o What were possible errors?
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Analysis Questions
1. DNA is soluble in water, but not in ethanol. What does this fact have to do with our method of extraction?
Explain what happened when the ethanol came in contact with the strawberry extract.
2.
A person cannot see single cotton thread 100 feet away, but if you wound thousands of threads together into a
rope, it would be visible at some distance. How is this statement an analogy to our DNA extraction?
3. In order to study our genes, scientists must first extract the DNA from human tissue. Would you expect the
method of DNA extraction to be the same for Human DNA? Why or why not? If you wanted to extract DNA
from a living person, what cells would you use and why?
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