Year 10 Essential Science
Name: ________________________
Department of Science 2018
Parade College, Semester 2
Total Mark:
/25
Strawberry DNA Extraction
Strawberries are excellent sources of DNA as the common strawberry has 8 times the amount
of a normal plants DNA. The plant is octoploid, with 8 sets of chromosomes in each cell.
Faulty cell division has produced this amount of DNA and it is quite common for plants (and
some animal tissues), to show polyploidy – more than 2 sets of chromosomes.
Aim:_______________________________________________________________________
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(2 marks)
Materials:
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Zip lock bag
teaspoon
chux cloth
beaker (250mL)
stirring rod
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detergent
salt
tap water
measuring cylinder
1 large strawberry
Conical flask + funnel
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Large test tube
Test tube rack
Method:
1. In a 250mL beaker, place 120mls of tap water, 4 teaspoons of detergent and ½ a
teaspoon of salt (this forms the extraction buffer). Stir gently.
2. Place strawberries in a zip lock bag. Remove all of the air to avoid popping the bag.
3. Squeeze and mash with your fingers for 2 minutes. Do not over mash as you will
break your DNA.
4. Add 6 teaspoons of your buffer to the mashed strawberries in the zip lock bag.
5. Reseal the bag and remove all of the air to avoid popping the bag
6. Squeeze and mix for another 2 minutes. Do not over mash as you will break your DNA
7. Collect a conical flask containing a plastic funnel.
8. Fold the cloth in half and place into the funnel
9. Cut the corner of the zip lock bag and place all of the mixture into the cloth filter
10. Allow the extract to drip into the beaker
Precipitate DNA
11. Pour the extract into a large test tube filling only to 1/3 ( approximately 5 ml)
12. Collect 10ml of ethanol in a measuring cylinder
13. Tilt the tube to 45° and slowly pour ice cold ethanol down the side of the tube. You
will need twice as much ethanol (about 10mL) as strawberry extract
14. The ethanol will form a layer above the extract. Between these layers is the
“interface” and you will see a pale layer form: this is the DNA
DISCUSSION:
1. Describe the material floating at the top of the test-tube after the alcohol was added.
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(1 marks)
2. What was the purpose of mashing up the strawberries?
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(2 marks)
3. The extract buffer that you added to the strawberry pulp was dishwashing detergent and
water. Why did we use this? (Hint: think about why you use detergent on dishes and clothes).
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(2 marks)
4. What happened when you added the ethanol to the strawberry extract? What purpose did
the ethanol serve? (Hint: think about the concept of “solubility”)
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(2 marks)
5. If you wanted to extract DNA from a living person, what cells would you use and why?
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(2 marks)
6. Why did we use strawberries as a specimen to extract DNA from?
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(2 marks)
7. Genes are found on chromosomes, and genes control traits. Give at least two examples of
traits that are expressed in the strawberry.
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(2 marks)
8. If 23% of the DNA in the strawberry had the nucleotide “Adenine”, what percentage would
have the nucleotide “Guanine”?
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(1 marks)
9. Draw a scientific diagram of the DNA double helix in the space below (include more than 1
nucleotide). The diagram must include the labels: nucleotide bases, sugar and phosphate
backbone.
(5 marks)
CONCLUSION: (*Were you successful at extracting the DNA? *From you results, what did you
observe? *What did you learn about DNA extraction? *What could you do to improve results
of this experiment?)
Remember to write your answer in full sentences.
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(4 marks)