Name
Date
Period / Accelerated Biology
Unit 8: DNA and Protein Synthesis

DNA Extraction from Fruit

Background Information

DNA extraction is the removal of DNA from the cells of an organism. In this exploration, we will be using a strawberry. Remember, both a cell wall and cell membrane surround plant cells and the DNA is contained in a membrane-bound nucleus. The first thing we need to do is remove these barriers. Plant cells are made of cellulose, a tough material that makes plants sturdy. Cell membranes and nuclear membranes are made up of a phospholipid bilayer. Strawberries are soft and easy to pulverize (breaking apart the cell wall). Soap is added to help dissolve the phospholipid bilayer that makes up the cell membrane and surrounds the nucleus. Strawberries also have large genomes; they are octoploid, which means they have eight of each type of chromosome in each cell. The DNA and organelles of the cell are mixed together. However, the DNA is in solution, which means the DNA is completely dissolved into the liquid and is not visible. The cell organelles at this point can be considered debris and can be removed from the solution because they are all clumped up together. Since we have broken the cell wall and cell membrane, we need to separate the DNA from the cell debris to visualize it. In order to visualize the DNA we must add alcohol (isopropyl) to the solution. DNA is insoluble in alcohol so it will separate out. At this point we will be able to remove it from the solution.

Pre-Lab Questions

  1. Predict and describe what you think you will see when you extract the DNA. What will it look like?
  2. If we wanted to look at a protein that codes for a portion of the stem of the strawberry, would we be able to find it in the DNA found in the fruit of the strawberry? Explain.

Materials

  • 10 mL DNA extraction solution
  • Alcohol (ice cold)
  • Cheesecloth
  • Funnel
  • Pipette
  • Plastic bag
  • Strawberry
  • Test tube
  • Wooden stick

Procedure

  1. Put your strawberry into your plastic bag, slowly pushing all of the air out of the bag when you seal it.
  2. Careful not to break the bag, mash the strawberry with your hand for about 2 minutes.
  3. Pour 10 mL of DNA extraction solution into the bag with the strawberry and reseal the bag.
  4. Continue mashing your strawberry for about another 2 minutes.
  5. Place your funnel into your test tube.
  6. Fold the cheesecloth and place it into the funnel to create a filter.
  7. Slowly pour the strawberry mixture from your bag through the funnel/cheesecloth into the test tube. Be careful not to get any strawberry gunk into the test tube. We only want the clear liquid part.
  8. All of your strawberry mixture will not fit into the test tube, so only fill your test tube about ½ way.
  9. Holding your test tube at an angle, use a pipette to slowly add the cold alcohol so your test tube is now ¾ of the way full.
  10. DO NOTstir, shake or disturb your test tube.
  11. Watch closely as translucent strands of DNA begin to clump together where the alcohol layer meets the strawberry extract layer.
  12. Carefully insert and rotate the wooden stick in the mixture to spool the DNA.
  13. Remove the stick and observe your strawberry DNA.

Analysis Questions

  1. Describe the barriers and processes that had to be broken down in order to get to the DNA. Explain what you did to break down the barrier or why you had to do the process, and why it worked. (HINT: You can start with information provided in the lab, but you should include more detail in your answer.)
  2. Describe how your procedure might be different if we used animal cells instead of plant cells. Would your end product look different? Explain.
  3. A person cannot see a single cotton thread 100 feet away, but if you wound thousands of threads together in a rope, it would be visible. Is this statement analogous to our DNA extraction? Explain.
  4. Research and cite two reasons as to why it is important for scientists to be able to remove DNA from an organism.

Conclusion

What kind of conclusion(s) can you draw from this lab activity? What did you learn? What could be done to improve this lab activity the next time around?