Strawberry DNA Extraction
Name
Period
Deoxyribonucleic acid (DNA) stores, copies, and transmits genetic information in all living cells. DNA is a
common thread connecting all organisms. 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 found in DNA include adenine (A), thymine (T), cytosine
(C), and guanine (G). The nucleotides covalently bind to a sugar phosphate backbone, known as deoxyribose. 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
1 strawberry (fresh or
frozen)
brown paper towel or coffee
filter
beaker
test tube
test tube holder
ice-cold 95% ethanol
DNA extraction buffer (50
mL detergent, 15 g NaCl (salt)
and 950 ml water
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 Record the qualitative data in the data table.
13 If there is time, repeat the process with the banana and or cheek cells.
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
nucleotide cytosine always pairs with
.
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?
and the