ࡱ> HJG'` *bjbj{P{P =N::*````$$===$hC="===CgXUUU= U=UU:I, >/ `G^u n0RL==U=====CCK =======d D  Name______________________________ Date________________ DNA Extraction Lab: Strawberry 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. Every cell in a strawberry contains eight copies of each of its chromosomes. As a result, strawberries contain large amounts of DNA. Strawberry DNA is easy to extract because strawberries are easy to mash, and ripe strawberries produce enzymes that contribute to the breakdown of cell walls. To extract the DNA, you will first break strawberry cells apart mechanically by crushing them. Next, you will add detergents to dissolve the cells plasma membranes. A filtering step then removes cell organelles, broken cell walls, membrane fragments, and other cell debris. The result will be a red-colored solution containing DNA and other small dissolved molecules such as sugars and proteins. When cold isopropyl alcohol is layered on top of this solution, molecules of alcohol repel the DNA molecules and the DNA molecules clump together. A ropelike clump of many DNA molecules forms that is large enough to see with the unaided eye. Pre-lab questions: 1. What do you think the DNA will look like? 2. Where is DNA found? 3. It is important that you understand the steps in the extraction procedure and why each step was necessary. Each step in the procedure aided in isolating the DNA from other cellular materials. Match the procedure with its function: PROCEDURE FUNCTION A. Filter strawberry slurry through cheesecloth ___ To precipitate DNA from solution B. Mush strawberry with salty/soapy solution ___ Separate components of the cell C. Initial smashing and grinding of strawberry ___ Break open the cells D. Addition of ethanol to filtered extract ___ Break up proteins and dissolve cell membranes  Materials: Heavy duty Ziploc bag 1 strawberry 10 mL DNA extraction buffer (soapy, salty water) Cheesecloth Funnel 50mL vial / test tube 1 coffee stirrer 20 mL ice cold isopropyl alcohol Watch glass Test tube rack Procedure: 1. Remove the green sepals from the strawberry. Place one strawberry in a Ziploc bag and seal the bag shut. 2. Smash/grind up the strawberry using your fist and fingers for 2 minutes. Careful not to break the bag!! 3. Add the provided 10mL of extraction buffer (salt and soap solution) to the bag. 4. Kneed/mush the strawberry in the bag again for 1 minute try not to make a lot of soap bubbles! 5. Assemble your filtration apparatus as shown above/right. 6. Pour the strawberry slurry into the filtration apparatus and let it drip directly into your test tube. Remove the funnel and discard any extra mashed strawberry pulp with the cheesecloth. 7. Slowly pour cold isopropyl alcohol into the tube pour the isopropyl alcohol carefully down the side of the tube so that if forms a separate layer on top of the strawberry liquid. 8. Watch for a minute. What do you see? Record your answer here: 9. Spin and stir the coffee stirrer in the tangle of DNA, wrapping the DNA around the stirrer. 10. Pull out the stirrer and transfer the DNA to the watch glass. The fibers are thousands and millions of DNA strands. 11. Clean up!! Rinse your funnel, test tube, watch glass Put the Ziploc back, cheesecloth, coffee stirrer and paper towels in the garbage. Conclusions and Analysis 1. What did the DNA look like? Relate what you know about the chemical structure of DNA to what you observed today. 2. Explain what happened in the final step when you added isopropyl alcohol to your strawberry extract. (Hint: DNA is soluble in water, but not in ethanol) 3. 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. Is this statement analogous to our DNA extraction? Explain. 4. Why is it important for scientists to be able to remove DNA from an organism? List two reasons. 5. Is there DNA in your food? ________ How do you know? Extension: Strawberry cells are octoploid (each cell contains eight sets of chromosomes), whereas banana cells are triploid (each cell contains three sets of chromosomes). Which do you predict will yield a greater quantity of DNA 5 grams of strawberry tissue or 5 grams of banana tissue? Prediction and explain why you think this: With a laboratory balance, measure 5 grams of strawberry tissue and 5 grams of banana tissue. 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