Discussion Questions:
1. 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).
Laundry /dishwashing detergents break down proteins and other organic compounds. That’s why we use them on our
clothes and our dishes. Destroying all the protein in the strawberry cells ensures that only the DNA is left behind.
2. What happened when you added the ethanol to the strawberry extract? What purpose did
the ethanol serve? (Hint: think about the concept of “solubility”)
The ethanol created a layer of fluid that laid on top of the strawberry / soap extract. DNA is soluble in soapy
water but not in ethanol. The ethanol acted like a “chemical magnet” that attracted DNA and suspended it in
solution.
3. A person cannot see a single cotton thread 100 feet away, but if you wound thousands of
threads together into a rope, it would be visible at some distance. How is this statement an
analogy to our extraction of DNA.
Rosalind Franklin
“Photo 51”: X-ray cystallograph of DNA
This picuture…
Led to this discovery
You cannot see a single strand of DNA with the naked eye, but when we extract millions and
millions of strands of it, we can see it.
By rotating the picture of
DNA 90 degrees, the more
familiar double helix is
now visible!
HOW COOL IS THAT!
4. In order to study our genes, scientists 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?
Cell are cells, regardless of the organism you are talking about. So the procedure for extracting DNA is basically
the same from strawberry to human to oak tree to duck billed platypus.
5. If you wanted to extract DNA from a living person, what cells would you use and why?
We could use cheek cells, skin cells or blood cells because they are easy to obtain. However, generating enough
cells to get a visible quantity of DNA is beyond what we can do in a high school lab. So we used strawberries
because… see #6 below.
6. Why did we use strawberries as a specimen to extract DNA from? (Hint: look up the
following link and read the first page:
http://strawberryplants.org/2011/02/genetics-of-strawberry-plants/
Strawberries have multiple sets of chromosomes. This is called polyploidy. It is interesting to note that while many
species of plants can get away with being polyploid, and can even be better for it, this is basically unseen in animals
So, while the genome of a strawberry is only a fraction of a human’s, each strawberry cell has tons more DNA per
cell than a human cell.