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Strawberry DNA Extraction 2009
PURPOSE/OBJECTIVES:
You will use regular household chemicals to extract DNA from strawberries and
other fruits. Each chemical has a specific purpose in the process of extracting DNA.
Scientists use a very similar process to isolate DNA from different organisms for study or
genetic manipulation.
By the end of this exercise, you should be able to:
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Visualize real DNA.
Explain what forms the genetic code.
Describe how the structure of DNA accounts for the way in which it replicates.
Understand that DNA is the genetic material of living organisms.
BACKGROUND:
Deoxyribonucleic acid, or DNA, is the genetic material that carries information
about an organism and is passed from parent to offspring. DNA is present in all organisms
including plants, bacteria, and humans. DNA is normally wound tightly around specialized
proteins called histones to form a higher order structure called a chromosome.
Chromosomes are contained within the nucleus of each cell.
When unraveled, a molecule of DNA looks like a twisted ladder, called a doublehelix structure. Watson and Crick used special photographs taken by Rosalind Franklin to
figure out the structure of DNA in 1953. The sides of a DNA ladder are made up of the
sugar, deoxyribose, alternating with phosphate molecules. Each rung of the DNA ladder is
made up of two nitrogen bases bonded together. There are four bases: adenine (A), thymine
(T), guanine (G), and cytosine (C). These bases always pair in a specific way, A with T and
G with C, to form the genetic code. Because of the particular pairing of nitrogen bases, the
sequence of the newly copied DNA strand exactly matches the order of the original DNA
strand.
VOCABULARY:
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
Strawberry DNA Extraction 200
DNA
Histones
Chromosome
Double-helix
Nitrogen bases
Genetic code
MATERIALS:
Per Group:
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Heavy-duty ziplock bag, quart size
Frozen strawberries, thawed overnight
20 mL DNA extraction buffer (water, salt, and soap) in bag
Ice water bath
Cheesecloth or coffee filter
Ice cold ethanol
Clear test tube
Wooden stick or paper clip
METHODS/PROCEDURE:
1. Add thawed strawberries to the extraction solution in the zip-lock bag. Close the bag,
squeezing out the air.
2. Crush the strawberries for 5 minutes. Be careful not to break the bag!
3. Place the bag of mashed strawberries in the ice bath for 1 minute. Remove the bag from
the water to carefully mix the strawberry solution by rocking the bag very slowly.
4. Repeat step 3 two more times.
5. Secure the cheesecloth over the beaker. Filter the strawberry solution through the cheese
cloth. Let the solution drain for 5 minutes. Transfer the filtered solution to a test tube.
6. Add 20 mL of ice-cold ethanol to the test tube by pouring it slowly down the side,
allowing it to rest on top of the strawberry solution. Do not agitate the solution.
7. Let the test tube sit for two minutes without disturbing it. The DNA will appear as
transparent, slimy, white mucus between the two liquids which can be spooled up with
the wooden stick or paper clip.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
Strawberry DNA Extraction 2009
Name: _____________________ Period: ___
METHODS/PROCEDURE FLOW-CHART: Fill in the chart below.
Add fruit to zip-lock bag.
Bag already has extraction solution.
Squeeze out air and close bag.
Crush fruit for 5 minutes.
Place bag on ice for 1 minute.
Mix by rocking bag slowly.
Secure cheesecloth to beaker.
Filter liquid through cheesecloth into beaker.
Transfer liquid to test tube.
Gently pour 20 mL ethanol into tube.
Do NOT disturb tube!
Collect DNA.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
Strawberry DNA Extraction 2009
Name: TEACHER'S NOTES Period: ___
QUESTIONS:
1. Describe the appearance of DNA. (Any observations about the extracted DNA.)
___________________________________________________________________________
___________________________________________________________________________
2. Where do we find DNA in the cell? DNA is found in the nucleus.
3. Would the DNA be the same in any cell of the human body? Why or Why not?
All the cells in a human body contain identical genetic information
because all the cells are descendents of the original fertilized zygote.
However, genetic information varies between individuals.
4. How do you remove DNA from a cell? First you must break open the cell and
dissolve the membranes (both plasma and nuclear). Then you remove the
DNA-associated proteins and precipate the DNA out of solution.
5. Each step in the extraction process has a specific function. Complete the table of
functions for each chemical used to extract DNA.
Chemical
Function
Soap/Detergent
Dissolves the lipid membranes
Salt
Removes associated proteins
Ethanol
Precipitates DNA
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Minority Science Programs – School of Biological Sciences – University of California, Irvine
Strawberry DNA Extraction 2009
DNA EXTRACTION BUFFER: Dissolve 15 g salt into 900 mL DI water, and then bring
up to 1L total volume by adding 100 mL dish soap or shampoo.
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Minority Science Programs – School of Biological Sciences – University of California, Irvine