Question

Much can be learned from studying an organism’s DNA. The first step to doing this is extracting DNA from cells. In this experiment, you will isolate DNA from the cells of fruit.

Materials (1) 10 mL Graduated Cylinder (2) 100 mL Beakers 15 cm Cheesecloth 1 Resealable Bag 1 Rubber Band (Large. Contains latex; please wear gloves when handling if you have a latex allergy). Standing Test Tube Wooden Stir Stick *Fresh, Soft Fruit (e.g., Grapes, Strawberries, Banana, etc.)

*Scissors **DNA Extraction Solution ***Ice Cold Ethanol *You Must Provide **Contains sodium chloride, detergent and water ***For ice cold ethanol, store in the freezer 60 minutes before use.

Procedure:

If you have not done so, prepare the ethanol by placing it in a freezer for approximately 60 minutes.

Put pieces of a soft fruit into a plastic zipper bag and mash with your fist. The amount of food should be equal to the size of approximately five grapes.

Use the 10 mL graduated cylinder to measure 10 mL of the DNA Extraction Solution. Transfer the solution from the cylinder to the bag with the fruit it in. Seal the bag completely.

Mix well by kneading the bag for two minutes.

Create a filter by placing the center of the cheesecloth over the mouth of the standing test tube, pushing it into the tube about two inches, and securing the cheesecloth with a rubber band around the top of the test tube.

Cut a hole in the corner of the bag and filter your extraction by pouring it into the cheesecloth. You will need to keep the filtered solution which passes through the cheese cloth into the standing test tube.

Rinse the 10 mL graduated cylinder, and measure five mL of ice-cold ethanol. Then, while holding the standing test tube at a 45° angle, slowly transfer the ethanol into the standing test tube with the filtered solution.

Figure 6: DNA extraction. The color has been enhanced by dying the fruit with a substance that glows under black light.

DNA will precipitate (come out of solution) after the ethanol has been added to the solution. Let the test tube sit undisturbed for 2 - 5 minutes. You should begin to see air bubbles form at the boundary line between the ethanol and the filtered fruit solution. Bubbles will form near the top, and you will eventually see the DNA float to the top of the ethanol.

Gently insert the stir stick into the test tube. Slowly raise and lower the tip several times to spool and collect the DNA. If there is an insufficient amount of DNA available, it may not float to the top of the solution in a form that can be easily spooled or removed from the tube. However, the DNA will still be visible as white/clear clusters by gently stirring the solution and pushing the clusters around the top.

DNA extraction experiment:

1. Identify one step which was included in the Virtual Lab which was not required in the hands-on experiment. Then, identify one step which was included in the hands-on experiment, but not the virtual lab. Why weren’t these steps required?

Answer 1

In the Virtual Lab cells for obtaining DNA sample, the cells are swabbed from a human subject to obtain DNA sample but fresh fruit are used in case of hands-on experiment. Smashing of the fruit was done in the hands-on experiment which was not carried out in virtual lab. Microcentrifuge is used for mixing of the concentration in the virtual lab. To get the DNA mixture out a cheese cloth and stick was used in case of hands on experiment. So, the microcentrifuge was not essential in virtual lab.