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Discovering DNA: Do Your Cheek Cells & a Strawberry Both Have DNA?

Difficulty
Time Required Average (6-10 days)
Prerequisites None
Material Availability A DNA extraction kit, listed in the Materials tab, is used for this project.
Cost Low ($20 - $50)
Safety Adult help is needed to cut a strawberry. The DNA extraction buffer is harmless if you touch it, but do not taste or swallow it.

Abstract

DNA is what makes you look like you. It contains your body's instructions for your hair and eye color, ear shape, your height, and much, much more. Do other living things also have DNA or is DNA only found in humans? You can answer that question yourself (and have your first look at your own DNA) by doing this project.

Objective

Extract DNA from your own cheek cells and then use the same procedure on a strawberry to see if it also has DNA.

Credits

Sandra Slutz, PhD, Science Buddies

  • Genes in a Bottle TM is a registered trademark of Bio-Rad Laboratories, Inc.

Cite This Page

MLA Style

Science Buddies Staff. "Discovering DNA: Do Your Cheek Cells & a Strawberry Both Have DNA?" Science Buddies. Science Buddies, 24 Oct. 2014. Web. 31 Oct. 2014 <http://www.sciencebuddies.org/science-fair-projects/project_ideas/BioChem_p042.shtml>

APA Style

Science Buddies Staff. (2014, October 24). Discovering DNA: Do Your Cheek Cells & a Strawberry Both Have DNA?. Retrieved October 31, 2014 from http://www.sciencebuddies.org/science-fair-projects/project_ideas/BioChem_p042.shtml

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Last edit date: 2014-10-24

Introduction

Why does your home look the way it does? Why is the kitchen not in the bathroom, or the bedroom not in the closet? Because carpenters used a set of instructions, called blueprints, to build your home. Building complicated things often takes good instructions, as shown in Figure 1, and people are no exception. You may not think of yourself as being "built," but, in fact, you look the way you do thanks to a set of instructions called DNA, short for deoxyribonucleic acid (pronounced dee-oxy-RYE-bo-NEW-clay-ik a-sid).

Both of these are instructions for building things.  On the left is a blueprint for a house.  
On the right is a diagram showing DNA. 
Biochemistry science project
Figure 1. Both of these are instructions for building things. On the left is a blueprint for a house. On the right is a diagram showing DNA—the instructions cells use to build your body.

DNA is material, made up of chemical units, inside every cell in your body. Most of your cells contain a full copy of the DNA instructions for what you look like. This full copy of DNA is called your genome. Your genome is responsible for your hair and eye color, how likely it is that you will get sick if exposed to a cold, and many other things that make you who you are. In fact, identical twins look the same because they have the same genome — their DNA is identical!

Although a genome contains an amazing amount of information, DNA is so small that even if you have an entire copy of your genome, it is too small to see. Even with the world's most powerful microscopes, it is difficult to see individual bits of DNA clearly! But you can see it if you get enough copies of your genome together. In this biochemistry science project, you will do exactly that. You will use the tools and chemicals in Bio-Rad's Genes in a BottleTM Kit to extract (pull out and separate) DNA from your own cheek cells. If you follow the instructions carefully, you will be able to easily see the DNA with your eyes — no microscope needed!

So now you know that humans have DNA and that is why they look the way they do. But what about other living things? How about a strawberry? What makes a strawberry look like a red fruit rather than a furry mouse? Does a strawberry also have DNA? You will use the same Bio-Rad kit to try to extract DNA from a strawberry. Then you can see if you and a strawberry are alike in one way: Do you both have DNA?

Terms and Concepts

  • DNA
  • Cell
  • Genome
  • DNA extraction

Questions

  • Why is DNA important?
  • If DNA is so tiny, how come you can see it after you extract the DNA in this experiment?
  • Do fraternal twins (twins who do not look the same) have identical genomes?
  • What are some other things around you that you think have DNA? What are some things that you think do not have DNA?

Bibliography

Check out these sources for more information about DNA:

Materials and Equipment

  • Bio-Rad's Genes in a BottleTM Kit. Available for purchase at Amazon.com. The kit includes:
    • Test tubes (2)
    • Measuring cups (2)
    • Transfer pipets (2)
    • Bottle of Bio-Rad DNA extraction buffer
    • Pendant vials and string for making DNA necklaces (2)
  • Drinking glass
  • Water; tap water or bottled water can be used
  • Permanent marker
  • Strawberry, fresh
  • Knife, specifically a butter knife or kitchen knife that can be used to cut the strawberry
  • Small bowl
  • Fork
  • Adult helper
  • Lab notebook

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Experimental Procedure

Once you have the Genes in A Bottle Kit and other materials, you can do this entire set of experiments in less than an hour.

Learning How to Use a Pipet

Before you start this experiment, take a moment to practice how to use a pipet. This will make the rest of the project much easier.

  1. Fill a drinking glass with water.
  2. Hold the bulb of the pipet between your thumb and pointer finger, as shown in Figure 2. Squeeze the bulb. Keep squeezing while you put the tip of the pipet into the water.
How to use a transfer pipet
Biochemistry  science project
Figure 2. Squeeze the bulb of the pipet to both suck up liquid and release liquid from the pipet. When sucking up liquid, the pipet tip should be in the liquid. When releasing liquid from the pipet, as shown in this picture, the pipet tip should be in the container you want to add the liquid to.
  1. With the tip of the pipet in the water, stop squeezing the bulb. This will create suction and cause water to be sucked into the bulb. The pipet should now be full of water.
  2. Pull the filled pipet from the water. Move the tip of the pipet so that it is inside another container — one of the measuring cups from the kit will work well for this. Slowly squeeze the bulb of the pipet again and the liquid will squirt into the container.
  3. Repeat steps 2-4 several more times until you can use the pipet well.

Extracting Your Cheek Cell DNA

The steps for this part of the experiment are the same as the DNA Extraction steps in the instruction manual that comes with your Genes in a BottleKit.

  1. Use the permanent marker to label one test tube "Human" so that you know it is the tube that contains human DNA.
  2. Use a pipet to fill the measuring cup to the 2.5 milliliter (mL) mark with water from the drinking glass, as shown in Figure 2. Save the pipet. You will use it again in step 5.
  3. Collect your cheek cells.
    1. Pour the water (2.5 mL) from the measuring cup into your mouth. Swish the water around while using your teeth to scrape/chew the insides of your cheeks gently. Do not swallow! Do this for about a minute - try humming your ABC's three times while you do this to make sure you have scraped and swished for long enough.
    2. Tip: This step will scrape off old cheek cells (do not worry, you have plenty more). The cheek cells contain DNA. But to get enough DNA to view with your kit, you need to collect lots of cheek cells. The more you swish and scrape, the more cells you will get and the better your results will be.
  4. Carefully spit your cheek-cell sample into your measuring cup.
    1. The sample will contain the water you started with (2.5 mL) plus saliva and the cheek cells you scraped off. There will now be more than 2.5 mL in the measuring cup.
    2. Pour all of the cheek-cell sample from the measuring cup into the test tube.
  5. Using your pipet, add DNA extraction buffer to the test tube until the liquid level in the test tube reaches the 20 mL mark.
  6. Put the cap on the test tube. Make sure the cap is on tight or it may leak!
  7. Slowly and gently turn the test tube upside down and then right side up again. Do this a total of five times.
    1. Tip: Do not shake the test tube! Shaking will break the DNA into such small pieces that you will not be able to see them.
  8. You should now be able to see your DNA. Look for fluffy, clear/white, stringy, web-like strands. Write your observations (what you see) in your lab notebook.
    1. Troubleshooting: If you do not see your DNA, you probably did not get enough cheek cells. Collect more cheek cells by repeating steps 2-4. Add the new sample of water, saliva, and cheek cells directly into the test tube; it is fine if adding the extra sample brings the total amount of liquid in the "Human" test tube to more than 20 mL. Repeat steps 6-7 and then look for DNA.
    2. Set this tube with DNA aside and try to extract DNA from a strawberry by following the next set of directions.

Looking for Strawberry DNA

This part of the project is similar to the cheek-cell DNA extraction, except this time you will mash a strawberry as your sample and see if the strawberry cells also contain DNA.

  1. Use the permanent marker to label the remaining test tube "Strawberry" so that you know it is the tube that contains the strawberry sample.
  2. Use the second pipet from the kit (the one you did not use during the cheek cell DNA extraction) to fill the measuring cup to the 2.5 mL mark with water from the drinking glass. Save the pipet. You will use it again in step 6.
  3. Have an adult helper cut a marble-sized piece of strawberry (approximately 1 centimeter all around) and place it in the small bowl.
  4. Pour the 2.5 mL of water from the measuring cup into the small bowl with the strawberry piece. See Figure 3.
Add water to strawberry for DNA extraction
Biochemistry  science project
Figure 3. To collect your strawberry-cell sample, start by putting a marble-sized chunk of strawberry in a small bowl. Add 2.5 mL of water to the bowl.
  1. Using a fork, mash the strawberry until it is mostly liquid. Make sure there are no large chunks left. Your mashed-strawberry sample should look similar to Figure 4.
    1. Tip: To make this a good test, you must mash the strawberry very well. Otherwise the extraction buffer that you add in step 7 will not be able to reach all the strawberry cells. If the buffer cannot react with all the cells, it cannot extract DNA - even if DNA is in the strawberries.
Mash strawberry with fork for DNA extraction
Biochemistry  science project
Figure 4. To make a good strawberry-cell sample, you must mash the strawberry until it is mostly liquid, as in this photo.
  1. Using the pipet, transfer the strawberry-cell sample liquid from the small bowl to the "Strawberry" test tube. This will be tricky. It will take several tries and some patience. As you use the pipet, the strawberry-cell sample in the pipet should look similar to Figure 5.
    1. Tip the bowl so that the liquid is easier to suck up with the pipet.
    2. The strawberry pulp may clog the opening of the pipet. If this happens, it is OK to put a little bit of pulp in the test tube, too. But avoid sucking up too much pulp because it will make it harder to see the DNA strands (if there are any) in the "Strawberry" test tube.
    3. Repeat this step, using the pipet. until you have transferred as much of the strawberry liquid to the test tube as possible. You will need to refill the pipet and transfer the liquid between the bowl and the tube several times.
Strawberry cell sample in transfer pipet for DNA extraction
Biochemistry  science project
Figure 5. Use the pipet to suck up the strawberry cell sample. Avoid as much as possible sucking up the pulp. This is tricky and will take several tries.
  1. Rinse the pipet with clean water from the drinking glass.
  2. Using your newly cleaned pipet, add DNA extraction buffer to the test tube until the liquid level in the test tube reaches the 20 mL mark.
Add DNA extraction buffer to strawberry cell sample
Biochemistry  science project
Figure 6. Once the strawberry-cell sample is in the test tube, it is time to use a clean pipet to add the DNA extraction buffer.
  1. Put the cap on the test tube. Make sure the cap is on tight or it may leak!
  2. Slowly and gently turn the test tube upside down and then right side up again. Do this a total of five times.
    1. Tip: Do not shake the test tube! If there is DNA in the strawberry-cell sample, shaking it will break the DNA into such small pieces that you will not be able to see it.
  3. Do you see any DNA? If you do, the strands will be fluffy, clear/white, stringy, and web-like.Write your observations down in your lab notebook.
    1. Troubleshooting: If you do not see any DNA, make sure you have enough strawberry cells in your test tube to draw a scientific conclusion. Repeat steps 3-6 and add the extra strawberry-cell sample directly to the test tube; it is OK if adding the extra sample brings the total amount of liquid in the "Strawberry" test tube to more than 20 mL. Mix gently as in step 10 and look for DNA.
  4. What can you conclude from your experiments? Do strawberries have DNA, just as humans do?

Ideas for Fun with Your DNA

If you would like to keep your DNA extraction(s), the Genes in A Bottle Kit comes with two pendants you can use to store the DNA. The kit even has directions on how to add food coloring to the DNA to make it more colorful if you prefer!

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Variations

  • If you would like to make your own DNA extraction buffer and explore some of the variables involved in a successful DNA extraction procedure, try one of these projects:

Share your story with Science Buddies!

I did this project I Did This Project! Please log in and let us know how things went.

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