First, You Need to Find Something That Contains DNA

First, You Need to Find Something That Contains DNA

First, you need to find something that contains DNA. Since DNA is the blueprint for life, everything living contains DNA.
For this experiment, we like to use strawberries. But there are lots of other DNA sources too, such as:

  • Spinach
  • Chicken liver
  • Strawberries
  • Broccoli

Certain sources of DNA should not be used, such as:

  • Your family pet, Fido the dog
  • Your little sister’s big toe
  • Bugs you caught in the yard

Materials per student:

  • 1 strawberry
  • 1 vial
  • 1 tsp of salt
  • 25ml extraction solution (20% solution of soap and water)
  • 1 wooden skewer
  • 1 plastic baggie
  • 5 ml of ethyl alcoholin a 10ml beaker
  • 1 coffee filter
  • 1 test tube
  • A pinch of meat tenderizer
  • 1 funnel
  • 1 pipette
  • Test Tube Rack (one per table)

Procedures – Day 1

  1. Obtain all materials
  2. Add the extraction solution, salt, meat tenderizer and strawberry (all of it, including the stem) to the baggie.
  3. Seal the baggie with minimal air.
  4. Make sure the baggie is completely sealed.
  5. Mash the contents of the baggie together for five minutes. DO THIS SLOWLY. The key is to keep the foam low.
  6. Slowly pour the strawberry mixture from the baggie through the coffee filter and funnel into a test tube (diagram to the left). You are filtering out all the large pieces of strawberry.
  7. You only need the test tube about half of the way full. Do not fill the test tube all the way to the top!!
  8. Let the mixture sit for 5 minutes.
  9. Tilt your test tube and slowly pour 5 ml of ethanol alcohol into your test tube. Pour the alcohol down the side of the test tube so that it forms a layer on top of the strawberry mixture.
  10. The DNA will rise into the alcohol layer from the strawberry layer.
  11. Record observations in your journal.
  12. Using the pipette, fill the vial about half full with ethyl alcohol.
  13. Use the wooden skewer to collect the DNA out of the test tube.
  14. Place the DNA into the vial with ethyl alcohol.
  15. Use the string to make an identification tag for your DNA sample. Label it with your name, period, and the test you will be performing (ex: Miss Buxton, p-2, expose to direct sunlight).
  16. Record observations in your journal.
  17. Clean up all materials.

Good Information

Alcohol is less dense than water, so it floats on top. Since two separate layers are formed, all of the grease and the protein that we broke up in the first two steps and the DNA have to decide: “Hmmm...which layer should I go to?”
This is sort of like looking around the room for the most comfortable seat. Some will choose the couch; others might choose the rocking chair.
In this case, the protein and grease parts find the bottom, watery layer the most comfortable place, while the DNA prefers the top, alcohol layer.
DNA is a long, stringy molecule that likes to clump together.

http://learn.genetics.utah.edu/units/activities/extraction/

Think about what you did and answer the following questions. Please use COMPLETE sentences and make sure to explain your

answers.

  1. Draw the DNA! Relate its chemical structure to how it looks when lots of it is clumped together.
  1. List 5 things available to you that you might use for a DNA source besides strawberries.
  1. List 5 things that would not be a DNA source.
  1. Explain why each of these materials were used to extract DNA:

a)What does the soap do?

b)What does the salt do?

c)What does the meat tenderizer do?

d)What does the alcohol do and why is it cold?

  1. Which ingredient do you think had the most effect on the amount of DNA you extracted? Describe an experiment that you could perform to test this.
  1. Do you think human DNA will look the same as strawberry DNA? Why or Why not?
  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 at some distance. How is this statement an analogy to our DNA extraction? Explain your reasoning.
  1. Why is DNA important to living things? Explain.

Want to conduct more DNA extraction experiments? Try out different soaps and detergents. Do powdered soaps work as well as liquid detergents?

An Explanation of the DNA Extraction Lab
Some basic, but cool, chemistry…

DNA is the largest known molecule. A single unbroken strand can contain millions of atoms. When DNA is released from a cell it typically breaks up into tiny strand fragments. These tiny fragments have a slightly negative electric charge. Salt ions, common in many solutions, are attracted to the negative charges on the DNA fragments and prevent them from adhering to one another. By controlling the salt concentration of the solution containing the DNA fragments, DNA can remain fragmented or become very “sticky” and form large globs.

Releasing the DNA…

The first step in obtaining DNA from any organism, be it a plant, animal, fungi, archae or bacterium, is to release the DNA from a cell. Detergents and soaps break down cell membranes, releasing the DNA, and they also break up proteins that may harm the DNA. Protein enzymes, or proteases, like those in contact lens solution or in “Ultra” forms of laundry detergent, can be used to further destroy proteins.

The meat tenderizer also helps to break down proteins and stops the enzyme action that breaks down the DNA.

DNA on a stick…

Once the DNA fragments are released into solution, the DNA can be spooled together by using ice-cold isopropyl alcohol. Alcohol allows DNA fragments to stick together, or precipitate, producing a blob of DNA that you can examine. When a small layer of alcohol is added to the top of a solution containing cellular fragments and DNA, it will form an interface where the DNA will precipitate, allowing it to be captured, or spooled, onto a wooden stick or glass rod. The colder

the ethanol, the less soluble the DNA will be in it. This is why it is important for the ethanol to be kept in the freezer or in an ice bath. Although this method is effective, the DNA produced is by no means pure; other materials such as protein and cell fragments are carried along.

Why Did I Add Detergent To My Strawberry?

Smashing separated the strawberry cells. But each cell is surrounded by a sack (the cell membrane). DNA is found inside a second sack (the nucleus) within each cell.

Why Did I Add Detergent To My Pea Soup

To see the DNA, we have to break open these two sacks.

We do this with detergent.

Soap and GreaseWhy detergent? How does detergent work?
Think about why you use soap to wash dishes or your hands. To remove grease and dirt, right?

Soap molecules and grease molecules are made of two parts:

Heads, which like water.

Tails, which hate water.

Soap and Grease

Both soap and grease molecules organize themselves in bubbles (spheres) with their heads outside to face the water and their tails inside to hide from the water.

When soap comes close to grease, their similar structures cause them to combine, forming a greasy soapy ball.

A cell's membranes have two layers of lipid (fat) molecules with proteins going through them.

When detergent comes close to the cell, it captures the lipids and proteins.

After adding the detergent, here is what you have in your strawberry soup.

In this experiment, meat tenderizer acts as an enzyme to cut proteins just like a pair of scissors.

The DNA in the nucleus of the cell is molded, folded, and protected by proteins.

The meat tenderizer cuts the proteins away from the DNA.

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