Instructions

Strawberry DNA Isolation Background: Strawberries have been selectively bred to be polyploid organisms. The interesting thing about polyploids is that they possess more than just a diploid genome, meaning that they have more than two sets of chromosomes! In the case of the commercial strawberry, it is an octoploid organism; it has 8 sets of chromosomes! The purpose of today’s experiment is to learn how to isolate DNA from plant cells. We will also learn the purpose of each of the different steps to understand how DNA can be isolated from the rest of the cellular content. Materials: Dish detergent (Used to dissolve the phospholipid membrane.) Plastic baggies (Used to homogenize the strawberries in the extraction buffer solution.) – Sodium chloride (Used to help remove proteins that are bound to the DNA, also to maintain the proteins insoluble in the aqueous layer so that they do not co-precipitate with the DNA.) – 4 Frozen Strawberries – Extraction buffer (see below) – 1 test tube (or tall glass) – cheese cloth (4 single layer sheets) – wooden stir stick – Ice cold isopropanol (“rubbing alcohol”) – beaker or large glass – rubber band – 50 ml graduated cylinder – Ethanol or Isopropanol (rubbing alcohol) – Used to precipitate DNA. The phosphates in the backbone of DNA are negatively charged and repel each other and form hydrogen bonds with water. Ethanol causes the water to be excluded. Once this happens, the negatively charged phosphates are attracted to positively charged ions such as sodium and clump together, forming the precipitate.) DNA Extraction Buffer Recipe: – 25 ml (or 1/8 cup) Dawn dish detergent – 4 g (or 1/2 tsp) sodium chloride (table salt) – water to 1/4 liter (half of a 500 mL soda bottle) Work Flow: Homegenize tissue Filter the extract Precipitate DNA Procedure: 1. Place 4 strawberries in a plastic baggy. 2. Homogenize the fruit by “squashing.” 3. Add 20 mL (4 tbsp) of the extraction buffer and squash for 2 additional minutes. 4. Make a cheese cloth filter by placing the cheese cloth over a 600 ml beaker and fasten it with a rubber band. 5. Filter the homogenized strawberry extract thr 4 single layers of cheese cloth into the beaker. (You may have to squeeze some of it through.) 6. Collect approximately 10 mL of the eluate (flow through liquid) and pour it into a test tube. 7. Add an equal volume (~10 mL) of ice cold isopropanol. 8. The precipitate should form immediately. It will look like bubbly mucus at the interface between the aqueous and organic layers of liquid. Do not shake this up! 9. Spool the DNA with the stir stick to pull it out.

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