Introduction to DNA

Introduction to DNA Strawberry DNA Extraction “An Excursion into Octoploidy”

Introduction:

This lesson plan is for the extraction of DNA from strawberries. Strawberries are an exceptional fruit to use for this lesson because each individual student is able to complete the process by themselves and strawberries yield more DNA than any other fruit (i.e. banana, kiwi, etc.).

Primary Learning Outcomes:

1. Students will observe first hand that DNA is in the food that they eat. 2. Students will learn a simple method to extract DNA and why each step is necessary due to the complex organization of DNA in cells. 3. Students will learn why it is important for scientist to extract DNA from organisms.

Background:

The long, thick fibers of DNA store the information for the functioning of the chemistry of life. DNA is present in every cell of plants and animals, and the DNA found in strawberry cells can be extracted using common, everyday materials. We will use an extraction buffer containing salt to break protein chains that bind around the nucleic acids, and dishwashing liquid soap to dissolve the phospholipid bilayers of the cell membranes and organelles, thus providing access to the DNA inside the cells. This will be assisted by the fact that strawberries are soft and easy to pulverize. They have large genomes and are octoploid, which means they have eight of each type of chromosome in each cell. Once the DNA has been isolated, it is not soluble in ethanol, and the colder the ethanol, the less soluble the DNA. For this reason the ethanol will be kept in the freezer or on ice. When

Science in Motion Wilkes University 2010 Page 1 ethanol is added to the strawberry extract, participants will observe the fine white strands of DNA precipitate. It will form cotton like fibers that will spool onto the stirring rod/inoculating loop/popsicle stick, and will look like a thick, clear glob of mucus when removed from the test tube because it is a macromolecule. DNA investigation can be used to determine paternity, evaluate evidence from a crime scene, or in determining the possibility of a genetic disease. It holds the key to unlocking the mysteries involving many important medical advances to be discovered in the future.

Pre-lab questions:

1. What do you think the DNA will look like? 2. Where is DNA found?

Procedures/Activities:

Step: 1 Duration: 10 minutes

If it is not provided, the teacher will prepare the DNA extraction buffer. In a bottle or large flask by adding 900mL distilled water, then 50mL dishwashing detergent (or 100mL shampoo), and finally 2 teaspoons salt. Slowly invert the bottle or swirl the flask to mix the extraction buffer, being careful not to produce a lot of suds or bubbles.

Step: 2 Duration: Approximately 45 minutes.

Materials: (For each student): heavy duty quart ziploc bag masking tape 1 large strawberry 50 mL test tube glass rod, bacterial inoculating loop, or popsicle stick 10 mL ethanol on ice test tube rack small graduated cylinder cheesecloth- 6 cm square, 2 layers thick small Funnel 10 mL DNA extraction buffer

Procedure: 1. Place one strawberry in a Ziploc bag. 2. Smash/grind up the strawberry using your fist and fingers for 2 minutes. Be careful not to break the bag!! 3. Add the provided 10mL of extraction buffer to the bag. 4. Kneed/mush the strawberry in the bag again for 1 minute.

Science in Motion Wilkes University 2010 Page 2 5. Assemble your filtration apparatus with the test tube in rack, funnel placed on top, and cheesecloth on top of funnel taped in place along each corner to the funnel. 6. Pour the strawberry slurry into the filtration apparatus and let it drip directly into your test tube. This may take 10-15 minutes; you can work on the drawings at this point in the procedure. 7. Holding the test tube at a 45 degree angle, slowly pour cold ethanol into the tube. OBSERVE ! 8. Dip the loop or glass rod into the tube where the strawberry extract and ethanol layers come into contact with each other. Twist slowly and spool upwards. OBSERVE! Assessment: Student Data Sheet

Name ______Date: ______

A. Answer the two Pre-assessment questions:

1. ______

2. ______

B. On the back of this paper or in your lab notebook, draw and label: 1. The filtration apparatus 2. The DNA extraction part of the experiment

C. Match the correct reason for the procedure to the experimental step. The steps are NOT in order.

1. ___ To precipitate DNA from solution 2. ___ Separate components of the cell 3. ___ Break open the cells 4. ___ Break up proteins and dissolve cell membranes

A. Filter strawberry slurry through cheesecloth B. Mush strawberry with salty/soapy solution C. Initial smashing and grinding of strawberry D. Addition of ethanol to filtered extract

D. .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 much further away. Using complete sentences, explain why this statement analogous to our DNA extraction.

E. Why is it important for scientists to be able to remove DNA from an organism? List two reasons.

Science in Motion Wilkes University 2010 Page 3 F. Make a Venn diagram and list 2 ways your DNA is like/unlike that of a strawberry in each section.

References

Knauft, D. Strawberry DNA extraction lesson plan. (Retrieved 8 June 2010) The Science Behind Our Food: College of Agriculture and Environmental Science, University of Georgia. 2004. Gemsclub.org/yahoo_site_admin/StrawberryDNAExtra.com4395135.pdf.

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