Name: __________________ Lab Partner: __________________
Date: ____________
DNA Extraction Lab
Have you ever wondered what DNA looks like? You are going to break apart the cell membrane of a
strawberry and separate the DNA from the nucleus. Strawberries are a good source of DNA because
they have 8 copies of each type of chromosome. This large number of chromosomes will filter out of
your solution and you will get to actually see DNA. We will be removing DNA from strawberry cells, so
it will be helpful to understand the structure of plant cells. All cells are surrounded by a cell membrane
that protects and contains its contents, but plant cells have an additional barrier, called a cell wall that
surrounds the cell membrane. The DNA is located within the cell’s nucleus. Notice that the nucleus has
a surrounding barrier, too, called the nuclear membrane. The other structures are called organelles or
“little organs.” They all have different, specialized jobs within the cell. We must break through three
barriers in order to remove the DNA from a plant cell; the cell wall, cell membrane, and nuclear
membrane.
Pre-Lab Questions: Complete Sentences!
1. Why are strawberries a good source of DNA?
2. Where in a plant cell is the DNA
located? In an animal cell?
3. What organelles to all plant cells
have?
4. What three barriers must we break through to remove DNA from a strawberry cell?
5. What do you think the DNA will look like when you extract it from the plant cell? (Hypothesize
the shape. I think that…because…)
Materials:
On Paper Plate:
1 Zip-lock bag
1 Coffee filter
1 Beaker
1 Funnel
1 plastic pipette
1 glass rod
Get from side counter:
1 Strawberry
10 mL DNA extraction buffer (soapy, salty water)
15 mL ice-cold ethanol in test tube
Procedure:
Part I- Preparing the DNA extract
Check off each step as you complete it.
1. Have one partner check off that all materials are on the lab table, while the other partner gets the
strawberry and removes the stem and leaves.
2. Place one strawberry in a ziplock bag.
3.
Mash up the strawberry for 2 minutes.
4. Add 10 mL of the extraction buffer to the ziplock bag.
5. Mash for 1 minute. While one partner is mashing, you should place the coffee filter in the funnel,
which is over the cup. Make sure the top part of the filter is folded over the top of your funnel
and that the bottom of the filter does not touch the bottom of the funnel.
6.
Pour the mashed strawberries with the extraction buffer into the filter and let drip into the
bottom of the cup. This takes about 10 minutes.
As you wait for your solution to filter, complete the following questions in complete sentences!
a. What was the purpose of mashing up the strawberry?
b. What does the extraction buffer do? (Hint: Extraction buffer contains soap. (What does soap do
when you wash your hands?)
c.
What does the filter do?
Part II: Pipetting the strawberry extract into the alcohol
7. One partner gets a test tube that contains ice-cold ethanol.
8. Using a pipette, remove some of the strawberry liquid from the cup and put into a test tube.
9. Place a glass rod into your strawberry test tube. Carefully pipette the alcohol into your tube with
strawberry and watch the solution precipitate (separate). DO NOT SHAKE THE TUBE!!! Very
gently swirl the tube once or twice. Take the glass rod and twirl it gently in the tube to collect
DNA on the glass.
Part III: Observations
10. Watch where the alcohol and extract layers come in contact with each other. Keep the tube at eye
level so you can see what is happening. What do you see appearing?
11. Sketch your procedure for the entire lab procedure, from prep to DNA extraction.
Include labels, equipment, and amounts for full credit.
Lab Step……
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Scientific Explanation….
Analysis Questions – Complete sentences for full credit!
1. What happened when you added the filtrate (filtered strawberry liquid) to the alcohol? HINT: DNA is
soluble in water, but not in ethanol. When substances are insoluble in a liquid, they precipitate out
(become a visible solid).
2. What does the DNA look like? Use 3 adjectives and as much detail as possible (color, texture, shape).
3. A person cannot see a single cotton thread four classrooms away. But if you wound thousands of
threads together into a rope, it would be visible at the same distance. How is this statement an analogy to
our DNA extraction?
4. For what purposes would a researcher want/need to extract DNA from an organism’s tissues?
Describe 3 reasons.
5. Why might some lab groups extract more DNA than other groups? List two sources of error with your
technique.
6. In order to study our genes (strands of DNA), geneticists 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?
7. Look at the plant cell pictured on page one of the lab handout. Remember that genes are found on
chromosomes, and genes control traits. Give two examples of traits that are expressed in the
strawberry.