DNA Science
Exercises
Handson activities to consider include making DNA
jewlry, isolation of DNA from material such as fruit and electrophoresis of DNA
or DNA like molecules. Kids can raise
and observe a genetically engineered pet, the GloFishTM and learn
about DNA science and genetic engineering.
A crime scene investigation theme works well with introducing DNA
science to groups of kids.
Isolation of Fruit DNA
Materials
Fruit such as bananas
Salt
Baking soda
Dish detergent (liquid)
Rubbing alcohol
Coffee filters or porous, non-absorbent cloth
(e.g. bed sheet pieces)
Large paper clips or tooth picks
Narrow bottle, jar or test tube; small bowl; spoon
or mortar and pestle
Procedure
1. “DNA extraction
solution”: add 1 tsp baking soda, 1 tsp
detergent and ¼ tsp salt to ½ cup of water in a mug or bottle.
2. Put ~ a ½ inch slice of
fruit in a small bowel and smash with a spoon or mortar and pestle.
3. Add 3-4 tbsp “DNA
extraction solution” to the bowl and grind (extract) with the spoon until the
fruit is well pulverized.
4. Place the cloth or filter
on top of a narrow bottle, jar or test tube and push part way in. Filter the DNA extract.
5. Add an equal volume of the
cold rubbing alcohol, mix by swirling.
Wait ~ 5 min. or more.
6. “Fish” out precipitated
DNA with paper clip hook. [straighten
large paper clip & make a small hook (~ 3 mm) at one end to “catch” the
DNA]
7. Show your catch!
See below for additional procedures to consider
for DNA isolation.
Making DNA models such as jewlry
Making DNA jewlry:
http://www.accessexcellence.org/AE/AEC/AEF/1995/ross_jewelry.html
DNA models using candy: http://tinyurl.com/z3pag
Electrophoresis
Genetically Engineered Pet
Kids can raise and observe a genetically
engineered pet, the GloFishTM and learn about DNA science and
genetic engineering. Many pet shops that
sell fish now have these GloFish. They
are small, inexpensive easy to raise fresh water fish that brightly glow in the
dark and the non-genetically engineered zebra fish do not. See: http://www.glofish.com/
for example.
Other fruit DNA extraction protocols
Be a Scientist - Extract DNA
from Banana in your
Kitchen! (http://64.233.187.104/search?q=cache:Ff97vXrBJDkJ:www.people.cornell.edu/pages/jl265/education.pdf+DNA+banana&hl=en&gl=us&ct=clnk&cd=3)
½ cup plain bottled water
¼ teaspoon uniodized salt
1 teaspoon baking soda
1 teaspoon shampoo (without conditioner)
2 teaspoons 91% isopropyl alcohol (well-chilled in freezer)
kitchen knife and fork
cutting board
coffee mug
1 banana
paper coffee filter
2 small containers with tight fitting caps (such as baby food jars)
Toothpick
Procedure:
1. Make a “DNA
Extraction Solution” by mixing the water, shampoo, salt, and baking soda in the
coffee mug. Mix well until all ingredients are dissolved.
2. Peel the banana
and cut off about ½ inch slice. Using the knife and fork mash it onto the
cutting
board until it is a gooey paste.
3. Measure about 1 level tsp of the mashed banana into one of the small jars and add 2 tbsp
of the
DNA Extraction
Solution prepared in step 1.
4. Cap the jar tightly and shake it vigorously while counting to 120.
5. Wet the coffee filter and place it (in a cone shape) into a small clean
jar.
6. Pour the banana/extraction
solution mixture from the first jar, through the coffee filter. Keep
the liquid that flows through the filter and discard the coffee filter with
the banana debris.
7. Add an equal volume of cold isopropanol (1 to 2 tbsp), cap the jar and
gently swirl the solution.
Long strands of DNA
should appear. It looks cloudy-white and will be stuck with tiny air
bubbles. Note: isopropanol should be used in a well-ventilated area.
8. Spool the DNA
onto a toothpick by slowly swirling it in the solution. Lift it out and touch it.
The DNA is the
slimy mass.
9. Eat the leftover banana.
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What's Happening?
Every living cell contains DNA.
This includes animals, plants, bacteria, and fungi. A membrane composed of
lipids and
proteins surrounds each cell.
Step 2: By mashing the banana
you are physically disrupting the cells and the cell membranes are broken open,
allowing the DNA
to escape.
Step 3: Mixing the banana
with the extraction solution allows the lipids and proteins to be solubilized
by the detergent
in the shampoo.
The baking soda in the solution acts as a buffer to keep the solution at an
optimal pH for DNA
(approx. pH = 7).
Step 6: When poured through the coffee filter the cellular debris is
trapped, however, the DNA
is able to flow through.
Step 7: The salt, in combination with the isopropanol, precipitates the DNA, because the DNA is not soluble in
isopropanol. This allows the DNA
to be seen by the naked eye. DNA
has a negative charge and the salt acts to
neutralize this charge so the DNA
can remain in its helix form.
Blender
protocol (http://biology.about.com/c/ht/00/07/How_Extract_DNA_Banana0962932481.htm)
1.
Gather together a
banana, salt, warm water, a blender, liquid soap, toothpicks or paper clips, a
strainer, a glass jar and rubbing alcohol.
2.
Cut your banana
into small pieces.
3.
Place your banana
pieces in the blender, add a teaspoon of salt and slightly cover the mixture
with warm water.
4.
Mix in the blender
for 5 to 10 seconds making sure the mixture is not too runny.
5.
Pour the mixture
into the glass jar through the strainer. You want the jar to be about half
full.
6.
Add about 2
teaspoons of liquid soap and gently stir the mixture. You should try not to
create bubbles when stirring.
7.
Carefully pour the
rubbing alcohol down the side of the glass stopping near the top.
8.
Wait for 5 minutes.
9.
Use the toothpicks
or bent out paper clips to extract the DNA that floats to the surface.
Tips:
1.
When pouring the
alcohol, make sure that two separate layers are being formed (The bottom layer
being the banana mixture and the top layer being the alcohol).
2.
When extracting
the DNA, twist the toothpick or paper clip slowly. Be sure to only remove the
DNA from the top layer.