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In this lesson, students extract DNA from cells
9, 10, 11, 12
By – Kelly
Primary Subject – Science
Grade Level – 9-12
Unit – Continuity: Reproduction and Inheritance
- The student will explain how a genetic trait is determined by the code in a DNA molecule.
- To recall important information about parts of the cells and their function; and to isolate DNA through the extraction of DNA from cells.
- Test tubes and test tube racks
- Split peas, broccoli, and bananas
- Meat tenderizer
- Cheese cloth
- Stirring rod
- Rubbing alcohol
- Where in the cell is DNA located?
- What components make up the membrane that surrounds the cell?
- What will happen to the cell without a cell membrane? How do you know?
- What other parts of the cell have membranes made up of lipids?
- Below are some questions you can ask your students before they begin the DNA extraction. This can be used as a drill or warm-up to recall information:
- This lesson can be done in many ways. The way I incorporate the lab into my class is that it is given after the structure and function of DNA is discussed. Also, your students need to have previously discussed the structure and function of the cell for both plant and animal cells.
- When you hear the term DNA, what comes to mind?
(You want your students to suggest stuff like 3D structure, double helix, hydrogen bonds, nucleotides, etc.)
- If you could see DNA with the naked eye, what do you think it would look like?
- Before the actual DNA extraction ask the class before you began.
- Students will conduct a DNA extraction from raw broccoli, bananas, liver, onions, and split peas. The extraction of pea DNA works really well. This extraction is something you can allow the students to complete themselves. The students need to read the procedure as a class or alone. I would suggest a discussion or questions time after reading the procedure to make students understand what is to be done. In the discussion, you can give the students some explanations as to why they are doing certain things or you can wait until after the lab is completed. Important information to give the students during the discussion is why detergent is added, why you use meat tenderizer and why alcohol is used.
- A helpful website is
- . As the students complete this activity, they should take notes of what they observe at the end of each step.
- 100 mL cup of food
- 1 mL table salt
- 200 mL cold water
- 1. Put in a blender:
- 2. Blend on high for 15 seconds. The blender separates the cells from each other, so you now have a really thin pea-cell soup.
- 3. Pour your thin pea-cell soup through a funnel that is lined with filter paper.
- 4. Add 30 mL of liquid detergent to the filtrate. Swirl to mix.
- 5. Let the mixture sit for 5-10 minutes.
- 6. Each group should be given 1/3 of a test tube of this mixture.
- 7. Add a pinch of enzymes (meat tenderizer) to each test tube and stir gently. Be careful! If you stir too hard, you’ll break up the DNA, making it harder to see.
- 8. Tilt your test tube and slowly pour alcohol (70-95% isopropyl or ethyl alcohol) into the tube down the side so that it forms a layer on top of the pea mixture. Pour until you have about the same amount of alcohol in the tube as pea mixture.
- 9. The alcohol causes the DNA previously dissolved in the detergent solution to become insoluble. The insoluble, white precipitate in the alcohol layer is DNA.
- 10. Hold the tube at a 45
- angle. Place the glass rod or skewer into the tube. Rotate the rod slowly. This process is called spooling. It is possible because the DNA is insoluble in alcohol. Spooling causes the DNA to separate from the solution, allowing you to gather it with a rod. *
Remember to rotate the rod slowly. Look carefully for the fine white threads accumulating around the rod.
- 11. Continue the process until no more DNA comes out of the solution.
- When the extraction is complete, lead a class discussion to answer the following questions:
- What did the DNA look like?
- What did you think of the DNA that you saw?
- Did you see what you expected? Why or why not?
- How was the DNA similar to and different from the way you thought it would be?
- Why might it be useful to extract DNA from cells?
- Place ESL students with a native English speaker or students not at ease performing labs with students that are comfortable doing lab. Also, I will constantly walk around the room and aid students in answering questions about procedures.
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