Strawberry DNA Extraction

Genetic Engineering is the modification and manipulation of an organism's genes using technology. Genes are made up of deoxyribonucleic acid, also know as DNA. DNA is a molecule that contains the genetic code for the development and functioning of an organism.

DNA is made up of four chemical bases: adenine (A), guanine (G), cytosine (C), and thymine (T). In humans, there are about 3 billon bases. The DNA bases pair up with each other to form base pairs — A with T and C with G.

Source: Healthline

Each base pair attaches to a sugar and phosphate molecule to form a nucleotide. Nucleotides are arranged in two long strands that form a spiral called a double helix, which looks like a ladder. The base pairs form the ladder’s rungs and the sugar and phosphate molecules form the vertical sides of the ladder. The order of the bases in a strand of DNA makes up a “sequence.” Knowing a DNA’s sequence is important because it tells scientist the kind of genetic information carried in that particular DNA segment.

DNA extraction is the process that scientist use to extract DNA from other cellular components so they can study it. There are various techniques to extract DNA but they all include 3 main steps:

  • Lysis of cell wall and nuclear membrane - This step breaks down the cell wall and nucleus to release the DNA.

  • Precipitation of DNA - This step separates the DNA from cellular debris.

  • Purification of DNA - This step washes and rinses of the DNA so it can be studied and stored .

Did you know?

  • Human beings may look different, but 99.9% of our DNA is the same

  • If one person's DNA was unraveled and placed end to end, it would stretch from Pluto and back.

  • Your DNA is 50% the same as a cabbage

Design Challenge:

Become a Geneticist by creating a DNA extraction kit to extract DNA from strawberries.

  • Do you think you will be able to see the DNA without using a microscope? Why or Why Not?

  • What does each ingredient do? (detergent, salt, alcohol)

  • Try experimenting with another fruit (ie: banana, kiwi etc). Did your results differ? Explain.

Materials included:

  • 1/2 tsp - Salt

  • Small bowl

  • Cheescloth

  • Funnel

  • Test Tube or small glass

  • Bamboo skewer

Materials Not Included:

  • 3 - Strawberries

  • 1/2 Cup - Isopropyl Rubbing Alcohol, 70%

  • 1/3 Cup - Water

  • 1 Tbsp - Dishwashing Liquid

  • 1 - Measuring Cup

Build Instructions:

  1. Chill the rubbing alcohol in the freezer. (You will need it later.)

  2. Mix ½ teaspoon salt, 1/3 cup water, and 1 tablespoon (tbsp.) dishwashing liquid in a glass or small bowl. Set the mixture aside. This is your extraction liquid.

  3. Line a funnel with the cheesecloth. Put the funnel's tube into a tall glass or test tube (Figure 1)

  4. Remove the green stems from three strawberries, put the strawberries in a plastic, re-sealable sandwich bag, and push out all the extra air. Seal the bag tightly.

  5. With your fingers, squeeze and smash the strawberries for 2 minutes. After this the strawberries should look like Figure 2.

  6. Add 3 tbsp. of the extraction liquid you made in Step 2 to the strawberries in the bag. Push out all the extra air and reseal the bag.

    • The liquid detergent will help break the strawberry cells open, allowing the DNA to spill out. The salt helps create an environment where the different strands of DNA can gather together in a clump, making it easier for you to see them.

  7. Squeeze the strawberry mixture with your fingers for 1 minute. After this the strawberries should look like Figure 3 below.

  8. Pour the strawberry mixture from the bag into the funnel. Let it drip into the glass until there is very little liquid left in the funnel (i.e., only wet pulp remains).

    • You may need to be patient as it can take some time for the liquid to filter through the cheesecloth.

    • Be sure not to let any pulp go around the cheesecloth and end up in the drinking glass below. If this happens, you will need to pour the liquid through the cheesecloth again, into a new drinking glass.

  9. Throw away the cheesecloth and the strawberry pulp inside. Pour the contents of the glass into the test tube or small glass jar so it is 1/4 full.

  10. Tilt the test tube or jar and very slowly pour ¼ cup of cold rubbing alcohol down the side.

    • The alcohol should form approximately a one-inch deep layer on top of the strawberry liquid. Also, do not let the alcohol and strawberry liquid mix.

  11. Study the mixture inside of the test tube or jar. The strawberry DNA will appear as gooey clear/white stringy stuff. Do you see anything in the jar that might be strawberry DNA? If so, where in the jar is it?

    • Hint: You know that the DNA precipitates into the alcohol layer, so that is probably where you will see some DNA.

    • Record your observations in your lab notebook.

  12. You can collect the DNA with a skewer or other thin rod. Dip the bamboo skewer into the test tube to where the alcohol and strawberry layers meet. Pull up the skewer. You should find some whitish, stringy stuff on the skewer, which is DNA containing strawberry genes! Did it work?

    • Record your observations in your lab notebook

Figure 1

Figure 2

Figure 3

Build instructions provided by Science Buddies

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