Strawberry DNA Prep: What the process looks like...

This recipe - METHOD - protocol was developed by Diane Sweeney (pdf files), a high school teacher in California.
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This laboratory activity will be published in Biology: Exploring Life

Notes:

• You can substitute 1 sheet of paper towel for the cheesecloth (less costly and easier cleanup).
• Moisten the cheesecloth or paper towel with some water from the faucet, then squeeze out excess liquid, for higher yields of juice.

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Method is from Diane Sweeney to be published in Biology: Exploring Life	Pictures are from Ms. Carole Forkey's class at Blue Ridge Virtual High School, Goochland, Virginia.
Rinse fresh strawberries. Thaw frozen strawberries at room temperature or in room temperature water. Do NOT try to thaw the frozen strawberries quickly by heat or microwave. (Heating will melt the DNA double helix and will coagulate the proteins in the fruit, affecting the ability of the detergent to solubilize the proteins that bind to the DNA). Prepare the shampoo/salt solution. Chill the alcohol..
Pluck off or cut away the green sepals.
Pop into a ziplock style plastic bag.
Smush for several minutes to completely crush the fruit.
Add 5 -10 ml of a solution containing non-phosphate liquid detergent (look for the ingredient on the label called sodium or ammonium laureth/lauryl sulfate, AKA SDS)or conditioner-free shampoo plus table salt (to prepare the solution see teacher instructions.)
Smush another few minutes. Be careful not to generate too many soapy bubbles!
Filter through a moistened paper towel or 2 layers (like two window screen layers) of cheescloth into a clear cup or test tube. Watch the teacher demonstrate proper filtration technique. DO NOT squeeze all the juice through so you can keep the pulp out.
Add 2 volumes (10 ml per 5 ml of juice) of ice cold 91% rubbing alcohol - available in a pharmacy (or 100 % isopropyl alcohol or denatured ethanol available in a school). Add carefully so the juice and alcohol layers stay fairly separate. If you can, chill or better yet, freeze the alcohol. The yield will improve.
Watch for development of several large air bubbles that have an attached cloud that begins to float up. The cloud is DNA!
Spool out with a thin glass rod, plastic coffee stirrer, plastic pipette. Spin and stir like making cotton candy. The yield is higher if you hold the tube at an angle.
Pull out the DNA. It will look like mucus or egg white, then as it dries, look more like spider web. The fibers are thousands and millions of DNA strands! To view in a microscope, put the glob on a clean slide and gently tease/stretch apart using 2 toothpicks or dissecting pins. The fibers will be easier to see in the teased-apart area.
Rinse out the tube and baggie and the spooler. If you used cheescloth and a funnel, rinse them out also, so students in the next class can use them too!

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