The Tree/Web of Life (Lesson 19: DNA the recipe for life)

DNA lab, let us extract some DNA from strawberries.
[ezcol_1quarter]Main Idea:[/ezcol_1quarter] [ezcol_3quarter_end]DNA is the molecule in the cell that has all the information necessary to make a living organism. One DNA molecule or chromosome is long and contains a list of characteristics necessary to make a fish, bird, dog, human, etc.[/ezcol_3quarter_end]

[ezcol_1quarter]Objectives:[/ezcol_1quarter] [ezcol_3quarter_end] 1. To isolate DNA from strawberries by following directions from the teacher and the handout.
2. To be able to write observations, analyze results, and make conclusions from the experiment.
3. To explain the reason behind each step in the experiment.

[ezcol_1quarter]Students’ Skills:[/ezcol_1quarter] [ezcol_3quarter_end] Observation, application, analysis, making use of knowledge, synthesis. These skills were drawn from Bloom’s Taxonomy and the constructivist list. NGSS connections: MS-LS1 From Molecules to Organisms: Structures and Processes; MS-LS3 Heredity: Inheritance and Variation of Traits.[/ezcol_3quarter_end]

[ezcol_1quarter]Materials[/ezcol_1quarter] [ezcol_3quarter_end] 1. For the lecture and discussion: textbooks, material reference, long strips of paper, and crayons.
2. Forthe activity: buffer (2 tsp of dishwashing liquid, 9 tablespoons of water and ½ tsp of salt), ripe strawberries, zip-lock bags, coffee filters, beakers, rubber bands, isopropyl alcohol, wooden coffee stirrers, toothpicks, measuring cylinders, and Eppendorfs or small glass vials.[/ezcol_3quarter_end]

[ezcol_1quarter]Lesson:[/ezcol_1quarter] [ezcol_3quarter_end]1. Entry card: Why do we call the nucleus the “control center” of the cell? What is in there? Allow time for students to ponder and write down their answers. Discuss the importance of this lesson, and how it relates to past lessons. During the discussion, remind students that the structure of DNA can be understood by using the book analogy.

2. Activity: “Strawberry DNA.” The students will extract DNA from strawberries. You can use other starting material, but fruits like strawberries are good because they are polyploid. Also, they smell good.

3. This class needs previous preparation. Have each station ready, with all the materials prepared. The students can work in pairs, but each needs to end up with his or her own bit of DNA. Follow the instructions on the handout.

4. Before starting the lab, have students read aloud the protocol, and ask questions. Inform them that you will be directing the steps so that everybody will be on the same step. Also, let them know that they will have plenty of time to think about what they are doing and why.

5. Start the lab and go slowly, making sure everybody is more or less in sync.

6. Once the lab is finished, go over the steps and the questions at the end of the protocol.

7. Exit card: “One thing that you have learned today” and “one concept you still do not understand.” Why do you think DNA is long and thin? (Hint: structure/function relationship and book analogy).


[ezcol_1quarter]Class Closing:[/ezcol_1quarter] [ezcol_3quarter_end]
1. Collect entry/exit cards.
2. Homework: Using the question at the end or your class handout, and in your own words, write the steps you took to isolate the strawberry DNA and the purpose of each step. You can illustrate your answer if you want. [/ezcol_3quarter_end]

[ezcol_1quarter]Assesment:[/ezcol_1quarter] [ezcol_3quarter_end] 1. Participation in class and discussions. Presentation of results, thoroughness and detail in their work.
2. Grading: Homework.
3. Use a general rubric to evaluate the students’ overall performance.[/ezcol_3quarter_end]

[ezcol_1quarter]Teacher’s Reflections[/ezcol_1quarter] [ezcol_3quarter_end]1. Things that I did not cover.
2. Did I meet the lesson objectives?
3. Comments, conclusions, and modifications.
4. Pedagogical value of the lesson. Did my students learn the concepts and ideas explored in this class? Did the assessments provide enough evidence of understanding?[/ezcol_3quarter_end]

[ezcol_1quarter]Notes to the Teacher[/ezcol_1quarter] [ezcol_3quarter_end] Teacher Reflection: This class was very interesting and enjoyable. The students and I loved doing this lab activity; they were very excited to obtain their little samples of DNA. Some students were also extremely disappointed when they did actually get any DNA. Like in real-life science, something went wrong during the extraction of DNA, and the experiment did not work. Two of these disappointed students came after class and asked me whether they could come back at lunchtime, and do the experiment again. Obviously I agreed; you never know whether you are taking to a future biologist. As it turned out, I had run out of materials for the next class, and I had to run to the store to get more. The two students appeared promptly at the beginning of lunch, and much to my displeasure I had to turn them away. I felt very disappointed that I could not repeat the lab for those students; however, there was a nice surprise a couple of weeks later. The day of the laboratory, I brought little glass vials so that the students could take their DNA home, if they wanted. All of them took the vials containing DNA with them, and showed it to everybody in school, and I suppose they also took it home. Two weeks later the issue of the DNA laboratory in the genetics section came up again in class, and one of the students still had his DNA vial in his backpack. I was very happy and secretly thought, “That kid will probably end up being a biologist.” I do not think I would change the laboratory lesson in any way because it was as good as it was going to get. The unseen variables that make each class unique will always present themselves.



DNA lab, let us extract some DNA from strawberries.

cropped-owlet_logo.gifDNA is the molecule in the cell that has all the information necessary to make a living organism. One DNA molecule or chromosome contains a list of characteristics necessary to make a fish, bird, dog, human, etc. Today we have a laboratory class; we are extracting DNA from strawberries!


YOUR ACTIVITY:  You will be working with a classmate, but each of you will produce your own DNA. Put on your scientist hats on, be curious, think of what each step means, be exact and analytic, and have fun. Follow your teacher’s directions.
1. Take the green leaf off your strawberry. Put the strawberry in the zip-lock bag, and try to get most of the air out.

2. Seal the bag. Use your fingers to smash the fruit as best as you can for about one to two minutes.

3. Add 15 ml of buffer to the bag and reseal it. Take as much air out as you can. Keep smashing the strawberries.

4. While you are mixing the fruit solution, your partner should place a coffee filter paper in a beaker and secure it with a rubber band. Make sure it does not touch the bottom of the beaker.

5. Pour the strawberry juice on top of the filter paper, and avoid pouring any chunks left in the fruit mix. Allow the juice to go through the paper. It may take a few minutes.

6. Hold the beaker containing the strawberry juice at a 45-degree angle and gently pour 15 ml of alcohol along the rim of the beaker.

7. Let the solution stand for two to three minutes. Observe the liquid. Do you notice anything?

8. Use a toothpick and roll it between your fingers (like eating spaghetti) to pick up the condensed material in the top of the solution.

9. Transfer the DNA to an Eppendorf (small plastic or glass container) and add more alcohol.

10. Answer the following questions. Use these answers when working on your homework assignment:

(a) Describe your strawberry DNA (color, shape, etc.).



(b) Where is the DNA found?



(c) How are you going to get the DNA from the inside of the cell?



 (d) How do you think the soap breaks the cell membrane? Think of why we use soap to wash dirty dishes.



(e) Alcohol dehydrates DNA; that is why it becomes insoluble and why you can see it.  Describe what your DNA looks like (color, texture, etc.)



(f) Write your own notes/question/doubts below: