Name: Date: Block: Berry Full of dna

Дата канвертавання19.04.2016
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Name:________________________________________ Date:_____________ Block:_____

Berry Full of DNA

Adapted from Juniata College Science in Motion Program
Pre- Lab Assignment:

  1. Read the Objective, Background and Procedure Section of the lab.

  2. Answer the pre-lab questions.

Objective: To Extract the DNA of Strawberries.

The native British wild strawberry is a "diploid" - it has 7 sets of two chromosomes, as in humans. However, the most commonly cultivated strawberry, Fragaria ananassa, is an octoploid with 7 sets of eight chromosomes. This makes it a good candidate for demonstrating DNA extraction - with eight copies of each gene in the strawberry genome, strawberries are packed full of it. The strawberry, it turns out, has a long and complicated family history. "The cultivated strawberry is interesting from a genomic perspective, because it's a polyploid hybrid species." Unlike peas, for example, or humans, for that matter, which are diploids (with two sets of chromosomes), a strawberry is an octoploid (with eight sets of chromosomes). How some strawberries evolved from diploids to octoploids is part of the story that people are trying to unravel.1

One of the reasons strawberries work so well is that they are soft and easy to pulverize. Also, ripe strawberries produce enzymes (pectinases and cellulases) which aid in breaking down the cell walls. Most interestingly, strawberries have enormous genomes. They are octoploid, which means they have eight of each type of chromosome (which equals abundant DNA).

The detergent in the shampoo helps to dissolve the phospholipid bilayers of the cell membrane and organelles. The salt helps keep the proteins in the extract layer so they aren’t precipitated with the DNA.

DNA is not soluble in ethanol. When molecules are soluble, they are dispersed in the solution and are therefore not visible. When molecules are insoluble, they clump together and become visible. The colder the ethanol, the less soluble the DNA will be in it yielding more visible “clumping.” This is why it is important for the ethanol to be kept in a freezer or ice bath.
Pre Lab Questions:

  1. How many TOTAL chromosomes do wild strawberries have?

  2. How many TOTAL chromosomes does the commonly cultivated strawberry, Fragaria ananassa, have?

  1. Identify two reasons why it is easier to extract the DNA of a strawberry verses an onion?

  1. Why is detergent used in the extraction process?

  1. Why is the temperature of ethanol important in this procedure?


  • Heavy-duty Ziploc bag

  • 1 strawberry (fresh or frozen)

  • DNA extraction liquid (soapy, salty water)

  • Filtering apparatus: cheesecloth, funnel, small beaker

  • Ice cold ethanol

  • Clear test tube

  • Glass stirring rod or plastic coffee stirrer

  • Microscope (optional)

  • 2 tooth picks (optional)


  1. If the green leaves on the strawberry have not yet been removed, do so by pulling them off.

  2. Put the strawberry into the Ziplok bag and smush for about two minutes. You need to completely crush the strawberry. You do not want this mixture to be really bubbly. The less bubbles the better.

  3. When you’re finished smushing, put 10 ml of the DNA extraction liquid into the bag.

  4. Smush for another minute. Be careful not to make too many soap bubbles.

  5. When you’re finished, place the cheesecloth into the funnel using enough to go over the rim of the funnel.

  6. Open the bag and pour some of the mixture through the cheesecloth and allow it to filter into the test tube. Allow only about 3 ml of liquid to filter through into the test tube.

  7. Next, carefully pour ethanol into the test tube filling it to 8.5 ml.

  8. Watch for the development of several large air bubbles that have a white cloudy substance attached to them. The cloudy substance is DNA!

  9. Take the glass stirring rod or coffee stirrer and spin and stir it like you’re making cotton candy. If you tilt the test tube, you’ll get more DNA.

  1. Pull out the DNA. It will look like mucus or egg white. As it dries, it will look like a spider web. The fibers are millions of DNA strands!

  2. Clean up!

    • Please throw away your: Ziploc bag, extra strawberry mush, cheese cloth, etc…

    • Wash all glassware and return to the tray.

    • Wipe up and clean any sticky surfaces.

    • Have you teacher check your lab station. TEACHER INTIALS_________________ (5pts)


  1. What type of macromolecule is DNA?

  1. What are the main elements found in DNA?

  1. What monomers make up DNA? What are the three parts of this monomer?

  1. What did the DNA look like?

  1. 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. How does this statement relate to our DNA extraction?

  1. Is DNA the same in any cell in the human body? Explain your answer.

  1. If you wanted to extract DNA from a living person, which cells would you use and why?


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