Strawberry DNA Extraction


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.

 

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