Strawberry DNA Extraction
Name
Period
Directions: Underline important information. Deoxyribonucleic acid (DNA) stores, copies, and
transmits genetic information in all living cells. This DNA is tightly associated with proteins known as
histones into tightly packed chromosomes. The genes located on the DNA transmit genetic information
from one generation to the next. Inherited traits depend on the chromosomal sorting in meiosis to determine
an offspring’s traits.
The digestion of nucleic acids, one of the main macromolecules found in organisms, provides the raw
material, or monomers of nucleotides to make DNA. The four nucleotides in DNA include adenine (A),
thymine (T), cytosine (C), and guanine (G). The DNA molecule includes a sugar-phosphate backbone with
paired nucleotide bases in the center. The nucleotides covalently bind to a sugar phosphate backbone.
Because of chemical properties, the adenine always binds with thymine (A=T) and the guanine always binds
with cytosine (G=C) to make a double-stranded molecule. The nucleotide base pairs (A,T,C, & G) form
hydrogen bonds. Then forms a double helix where the two strands of DNA twist around each other, looking
like a twisted ladder.
Purpose – extraction of DNA from a strawberry and understanding and analyzing the structure and function of
DNA
Safety Precautions
-Do not eat or drink in the laboratory
-Wear an apron and safety goggles
Materials
heavy duty zip-lock baggie
beaker
DNA extraction buffer (50 mL
1 strawberry (fresh or frozen)
test tube
detergent, 15 g NaCl (salt) and
950 ml water
brown paper towel or coffee
test tube holder
filter
ice-cold 95% ethanol
Procedure:
1. Place one strawberry in a zip lock baggie and carefully press out all of the air and seal the bag.
2. Carefully, but thoroughly, smash the strawberry for 2 minutes to break open the cell.
3. Add 10 ml extraction buffer to the bag and carefully press out all of the air and seal the bag. Remember
nuclear and cell membranes are made of lipids (fats)! What does soap do to lipids?
4. After adding the extraction buffer and resealing the bag, mush carefully again for one minute.
5. Place the paper towel or coffee filter over the beaker and make an indentation or depression
6. Slowly, and a little at a time pour the strawberry mush into the indentation.
7. Carefully, use your fingers to push the filtrate through the paper towel. Discard the baggie and the mashed
strawberry. If the paper towel breaks filter again into another beaker.
8. Pour the filtrate into the test tube provided
9. SLOWLY!!!! Pour the ice-cold alcohol into the tube until a clear layer about 2 cm thick is formed over the top
of the strawberry extract. The alcohol causes the DNA to precipitate out of solution. This step must happen
very slowly for optimal results.
10. At the interface (between the mush and ethanol), the DNA precipitate will be floating at the top.
11. Spool or scoop the DNA on your glass rod or wooden coffee stirrer.
12. Observe the DNA. It contains many tiny strands clumped together.
Use the information found in the introduction to answer the Questions Below- RSQ
1. Match the above lab component to the function in extracting the DNA. Read carefully.
Match the purpose of each step of extracting DNA
_____1. Break open the cell
_____2. Dissolve cell membranes
_____3. Precipitate (clump together) the DNA
_____4. Separate organelles, broken cell wall, and
membranes from proteins, carbohydrates, and DNA
A. Squish the fruit to a slush
B. Filter extract through paper towel/filter
C. Mix in a detergent solution
D. Layer cold alcohol over the extract
2. Describe what the DNA looked like.
3. What are three functions of DNA?
4. What hereditary component is located on the DNA?
5. What macromolecule provides the nucleotides for making DNA?
6. In the DNA molecule the nucleotide base adenine always pairs with
cytosine always pairs with
.
and the nucleotide
7. Label the DNA molecule to the right with the type of bonds, corresponding nucleotide base, backbone, and
nucleotides.
8. Based on the reading, what would be the last step in properly representing the model to the right?