Extraction of DNA

This lesson plan may be used to address the academic standards listed below. These National Science Education Standards are drawn from Content Knowledge for The Human Body and Nutrition. The science subject matter focuses on the science facts, concepts, principles, theories, and models that are important for all students to know, understand, and use.

Subject: Science; Grades 3-4

Purpose: The students will successfully extract DNA from wheat germ.

Student Learning Outcomes:

  1. Examine the results of the DNA extraction process.
  2. Diagram the procedure and label all materials with 100% mastery..
  3. Explain the purpose of each reagent with 85% mastery.
  4. Describe the appearance of DNA from wheat germ.

Prior Knowledge: As a complement to the abilities developed in the science as inquiry standards, the students have developed abilities to identify and state a problem, design a solution--including a cost and risk-and-benefit analysis--implement a solution, and evaluate the solution. Students know DNA is a substance required for a plant or animal to inherit their parents’ physical traits. The DNA fibers are in every cell of the human body and the information prescribes how a particular cell will function. DNA makes up genes; genes make up chromosomes. These are the genetic materials for each living thing. The DNA is a tightly wound coil and with the right conditions these coils will spring out and separate from the other materials. Today we are going to extract DNA and examine the qualities of this essential material.

Materials:

Teacher and Students:

·  250 mL beaker

·  100 mL water, tap water acceptable

·  l½ g raw (not roasted) wheat germ

·  5 mL of Athletic Shoe Cleaner-Deodorizer or dish soap

·  3 g of Adolph’s 100% Natural Tenderizer, unseasoned

·  10 mL of alcohol (from the freezer)

·  sodium bicarbonate solution to produce a ph of 8

·  1 thermometer

·  glass rod

·  pH paper

Students:

·  Individual test tubes

·  Filter Paper

Procedure: (TEACHER MAINTAINS WATER BATH—STUDENTS WEIGH MATERIALS):
1. Prepare water bath at 55 degrees Celsius
2. Fill 200 mL beaker with 100 mL water and place into water bath. Mix in 1.5 g wheat germ with plastic spoon into beaker until dissolved as much as possible.
3. Add 5 mL dish soap. Maintain temperature at 55 degrees C and stir occasionally. CAUTION: Do not allow temperature to exceed 60 degrees C because this may denature DNA.
4. Dissolve 3 g meat tenderizer in the wheat germ solution and add 10 mL baking soda solution. Maintain the temperature at 55 degrees C for 10 minutes.
5. Place the solution on ice for 15 minutes.
6. Using the 10 mL graduated cylinder, gently layer 10 mL of 95% ethanol over the solution, forming a second layer.
7. Use the glass rod to spool the DNA which precipitates at the interface. DO NOT STIR at the bottom or you will disturb the waste wheat germ.
8. Pull as much DNA out of the solution as possible and place on the filter paper to dry overnight.
9. Weigh the DNA you isolated.

Behavior Expectations: Today we will be performing an experiment. Some of the materials we are going to use are messy. I expect you to be careful and abide by the safety rules when using the materials. I expect the proper clean-up after the experiment.

Motivation: How many of you have seen DNA? How can we pull the DNA out of the plant material we are using today and observe it? The students know the cell nucleus contains DNA and all the material parents pass on to the child. The students know that their DNA is unique and may be used as a fingerprint to identify them.

Data Collection:

Experimental Procedure (See Attachment)

  1. Tell students today’s lesson will focus on the extraction and examination of DNA material.
  2. Students perform experiment with the assistance of their team, explaining the process to each other as each step is performed.
  3. Once procedure is complete, each student obtains a sample in their individual test tube to examine and complete tasks.
  4. Assistants circulate and add the alcohol to the test tubes.
  5. Students begin observing the separation of the liquids and the extraction of the DNA.

Data Confirmation of DNA

  1. Teacher circulates and helps students see the multiple layers and the DNA particles as they separate in the individual test tubes.
  2. The DNA concentrate is collected and dried on filter paper.
  3. The class collects the precipitates and they are dissolved in deionized water with a small amount of sodium chloride.
  4. This will yield an acidic solution and the student will confirm this with a pH meter.
  5. The students will complete the given task of making a diagram, labeling the materials, explaining the purpose of each reagent, and describe the appearance of the DNA.
  6. The teacher will circulate and support students’ individual work.

Debriefing and Checking for Understanding:

Data Processing:

  1. The teacher will establish a time for bringing closure to the experiment and procedures.
  2. The teacher will summarize the extraction and examination of the DNA.
  3. Student input will be accepted to close the lesson.

Appraisal: Those not reaching mastery will be required to perform another lab for accepted accuracy score. Students must complete all tasks with an 85% accuracy to reach mastery. Rates below mastery require that the task be performed until 85% accuracy is reached.

Extended Practice: Visit a Forensic Science Lab or have a guest speaker talk about the collection of evidence for DNA to identify a plant or animal.

References:

Davis, S.B. (1992). Extraction of DNA Using Household Products.

University of Florida, ICBR, Gainesville, FL.

Additional Readings:

DNA is Here to Stay (Cells and Things)

Frances R. Balkwill, Dr. Fran Balkwill, and Mic Rolph; Carolrhoda Books, 1994

DNA and Genetic Engineering (Cells and Life)

Robert Snedden, Heinemann, 2002

Genetics (Discovery Channel School Science)

David Krasnow, Gareth Stevens Publishing, 2003

My First Book about DNA

Katie Woodard, Xlibris Coporation, 2002