Human DNA Extraction (Ryan Hendrickson)
Title: Human DNA Extraction (Ryan Hendrickson).
Principle(s) Investigated: The structure of cells, DNA is present in cells, How soap/salt solution effect cells.
Cell Biology (9-12th)
1.a Students know cells are enclosed within semipermeable membranes that regulate their interaction with their surrounding
1. h. Students know most macromolecules (polysaccharides, nucleic acids, proteins, lipids) in cells and organisms are synthesized from a small collection of simple precursors.
5.a. Students know the general structures and functions of DNA, RNA, and protein.
Materials:
1 Human
Sandwich Bags or Drinking Cups
0.9% salt solution (2tsp salt in 1L water)
Detergent mix (25% detergent, 75% water)
Rubbing Alcohol
Plastic pipette
Microcentrifuge tube (optional)
1 Spool of string (optional)
Procedure: Give a detailed explanation of the procedure and include diagrams if possible.
1. Fill a cup halfway with the 0.9% salt solution (prepared previously).
2. Swirl salt solution around in mouth for approximately 1 minute (similar to when you use mouthwash)
3. Spit out salt solution back into the cup.
4. Add approximately 2mL of the detergent mix to the cup and gently swirl the cup around several times for approximately 1 minute.
5. Pour contents into a labeled test tube.
6. Add between 2-4mL of rubbing alcohol to the test tube. Be sure to do this slowly by pouring the rubbing alcohol down the side of the cup. Do not to mix!
7. Wait 1 minute for DNA to precipitate out into the alcohol layer.
8. Using a plastic pipette, transfer the DNA into a microcentrifuge tube.
9. If necessary add more rubbing alcohol to microcentrifuge tube.
10. Using the string make a necklace to show all of your friends!
Student prior knowledge: What prior concepts do students need to understand this activity?
To understand this activity students need to know that all living things are made up of cells. Also they need to know about the general structure of membranes present in the cell (both the cell membrane and nucleus being made up of a phospholipid bilayer with hydrophobic and hydrophilic parts). Students also need to know the general structure of DNA and that it is present in all living cells.
Explanation: Give a thorough explanation of the experiment or demonstration. Your explanation should be written to give your fellow teachers a solid understanding and include greater detail than what you might provide for your secondary students. Make certain to include equations whenever pertinent.
It is one things to teach someone that we are made up of cells and that we have DNA that codes for all of our characteristics and features. But it is something entirely different if you can show them. This experiment is simple and can be done with household items. The salt solution that the student gargles helps remove cheek cells and partially lyse them. When the detergent solution is added it helps break up the cell membranes further by forming micelles around sections of the phospholipid bilayer. The contents of the cells are then present in the liquid (DNA, proteins, etc.), so when the alcohol is added the DNA is able to precipitate into the alcohol layer because it is not soluble in ethanol. The DNA will become noticeably visible in the alcohol layer as thousands of DNA strands clump together, and can then be extracted easily.
Questions & Answers: Give three thought-provoking questions and provide detailed answers.
1. Would it be possible to extract DNA from other animals? What about plants?
a. Yes, although it would be pretty difficult using this method it is possible to extract DNA from animals. Since animals are made up of cells, they contain DNA just the same as people. DNA is also extractable from plants because they are made up of cells. In fact a similar procedure can be done to extract DNA from plants, and you get a lot more DNA!
2. Could this procedure still work if salt and soap were not used?
a. Technically it would still be possible for the procedure to work. The reason why we use salt and soap is to help break up the cells, in order to expose the DNA. This can be done by physical shearing of cells, but it is much more difficult to accomplish cell lyses. When salt water is used it can break the cell membrane because the cell is in a hypotonic solution. In saltwater the cell is in a crenation state, severally wrinkled due to water loss, and has a greater potential to lyse. Then when soap is added it further breaks up the cell membrane to completely lyse the cell.
3. Is the extracted solution purely DNA?
a. No! Both DNA and RNA are present in the extracted solution. There is no purification step in this procedure to isolate just the DNA. In fact we are also isolating DNA from bacteria in your mouth!
Applications to Everyday Life: Explain (don't just list) three instances where this principle can be used to explain other phenomenon.
- The use of the detergent to break up the phospholipid bilayer is similar to the how detergents work to clean dishes. The soap breaks up the oils and fats left by food. (Can be shown with the milk and food coloring)
- Being able to extract DNA from cells is important in determining your genetic makeup. This is important in understanding what diseases you are more susceptible to, allowing you to take preventative measures. (Ex: 23andme)
- Every person has a unique genetic code that is exclusive to him or her. DNA is more reliable and efficient in identifying people than fingerprints and is very important in the field of forensics.
Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.
Videos: Include links to videos posted on the web that relate to your activity. These can be videos you have made or ones others have made.
This experiment can also be done with fruit, such as Strawberries.
DNA Video (Part 1) (Part 2) (Part 3) (Part 4) (Part 5)
"Extract Your Own DNA from Cheek Cells." Extract Your Own DNA from Cheek Cells. Web. 10 Feb. 2012. <http://www.seplessons.org/node/222>.
Portillo, Melissa. "Strawberry DNA Extraction (Melissa Portillo) - 525s12." Web. 9 Feb. 2012. <https://sites.google.com/site/sed525s12/previous-demonstrations/demonstrations-fall-2011/strawberry-dna-extraction>.