Adapted from a lab by C. Sheldon
Introduction:
DNA is found in cells from
Animals and Plants. DNA is a double stranded macromolecule composed of
nucleotide bases pairing Adenine with Thymine and Guanine with Cytosine.
DNA can be extracted from cells by a simple technique with household chemicals,
enabling students to see strands of DNA with the naked eye.
Purpose:
To extract DNA from the fruit
of a strawberry plant
Safety
Precautions:
Materials
/ Equipment (per student group):
1. heavy duty
zip-lock baggie
2.
1 strawberry
(fresh or frozen and thawed)
3.
cheesecloth
4.
funnel
5.
100 ml beaker
6.
test tube
7. wooden coffee stirrer
8. DNA
Extraction Buffer (One liter: mix
100 ml of shampoo (without conditioner), 15 g NaCl,
900 ml water OR 50 ml liquid
dishwashing detergent, 15 g NaCl and 950 ml water)
9.
Ice-cold 95%
ethanol or 95% isopropyl alcohol
Procedure:
1.
Place one
strawberry in a zip lock baggie and carefully press out all of the air and seal
the bag.
2.
Smash the
strawberry with your fist for 2 minutes.
3.
Add 10 ml
extraction buffer to the bag and carefully press out all of the air and seal the
bag.
4.
Mush again for
one minute.
5.
Filter through
cheesecloth in a funnel into beaker. Support the test tube in a test tube rack.
6.
Discard the
extra mashed strawberry.
7.
Pour filtrate
into test tube so that it is 1/8 full.
8.
Slowly pour
the ice-cold alcohol into the tube until the tube is half full and forms a layer
over the top of the strawberry extract.
9.
At the
interface, you will see the DNA precipitate out of solution and float to the
top. You may spool the DNA on your glass rod or pipette tip.
10.
Spool the DNA by dipping a pipette tip or glass rod into the tube
right where the extract layer & alcohol are in contact with each other. With
your tube at eye level, twirl the rod & watch as DNA strands collect.
Prelab:
Take a look at the sketch of the plant cell below.
The chromosomes (which are made of DNA) are in the nucleus. This is the only
place where DNA is located.
Now match the procedure with what it is doing to help isolate the DNA from the
other materials in the cell.
|
_____1. Break open the cell |
A. Squish the fruit to a slush |
|
_____2. Dissolve cell membranes |
B. Filter your extract through cheesecloth |
|
_____3.
Precipitate the DNA (clump the DNA together |
C.
Mix in a detergent solution |
|
_____4.
Separate organelles, broken cell wall, and
membranes from proteins, carbohydrates, and DNA |
D.
Layer cold alcohol over the extract |
DNA Extraction Table
|
AMOUNT ADDED OR OBTAINED |
INITIAL COLOR |
PURPOSE |
|
| BUFFER (soap-salt mixture) |
|||
| STRAWBERRY | |||
| COLD ALCOHOL | |||
| DNA |
SKETCH OF TEST TUBE WITH CONTENTS
|
|
Questions:
1.
Where can DNA
be found in the cell?
2.
Discuss the
action of the soap (detergent) on the cell. What is the purpose of the
soap in this activity?
3.
What was the
purpose of the Sodium Chloride? Include a discussion of polarity and charged
particles.
4.
Why was the
cold ethanol added to the soap and salt mixture?
5.
Describe the
appearance of your final product?
6.
Draw a diagram
of DNA containing 5 sets of nucleotide bases labeling the hydrogen bonds
between the bases.
