Did you see DNA before?
https://www.stevespanglerscience.com/lab/experiments/straw
berry-dna/
1
Activity 3 : DNA Extraction
1.
Objective of experiment
To extract DNA from strawberries with washing-up liquid.
2. Apparatus and Materials
•
•
•
•
washing-up liquid (detergent)
salt
ice-cold alcohol
ice bath
2
Activity 8.2
3.
Follow the procedures to extract DNA.






Grind strawberries with a pestle in the mortar.
Add about 10 mL washing-up liquid, 1/2 teaspoon
salt and approximately 30 mL tap water to the
grinded strawberries. Stir the mixture gently for 1
minute.
Filter the mixture through a muslin cloth into a
test tube, about 1/3 full, to separate strawberries
from the clear liquid.
Double up the volume of the mixture by adding
alcohol slowly into the test tube.
Leave the mixture undisturbed for 2 – 3 minutes in
an ice-bath until no emergence of bubbles.
Swirl a toothpick around the interface of the two
layers formed inside the test tube. Long and
stringy threads can be picked up.
3
Activity 2: Questions
1.
What is the purpose of grinding the strawberries?
To break down the cell wall, cellular membranes and nuclear
membranes.
2.
Where is the DNA of the strawberries?
In the cell nucleus.
3.
What is the function of detergent in step 2?
Soap dissolves cell membranes so that DNA is liberated.
4
Activity 8.2
Questions (optional)
4.
What is the function of salt in step 2?
Salt solution helps the DNA strands come together.
5.
What happens when alcohol is added to the solution in step 4?
DNA is soluble in water and will appear clear in water. But DNA is
insoluble in non-polar solvent, such as alcohol. Therefore, DNA will
precipitate (solidify and appear) out of alcohol. Of course, this is
not pure DNA.
5
Follow-up Discussion
Write down your answers
on a piece of paper.
6
Activity 2
Follow-up Discussion Questions
1.
Do you think your results would be different
if you use a vegetable or fruit other than
strawberries, say, onion, kiwi fruit, broccoli,
banana (without skin)? Explain.
2. Do different organisms have the same DNA?
3. At a crime scene what evidence would you
collect in order to extract DNA? List as
many as possible.
7
Activity 2
Answers:
1. DNA can be easily extracted from many different
plants. The amount of DNA extracted depends upon
many factors, including the number of cells crushed,
and whether the cells can be easily broken apart.
2. Though all DNA molecules are made up of similar
chemical components, different organisms have
different DNA molecules due to the different base
sequences of the bases — A, T, G, and C, which makes
a specific organism have distinctive characteristics.
3. Blood (white blood cells), saliva, skin scalp, hair and
etc.
Note that DNA is found in nearly every cell in the body.
But one significant exception is red blood cells (lack
8