DNA Extraction of Wheat Germ Introduction National Science Education Standards Lesson Introduction All life functions within a plant are controlled by the genetic material found within its cells’ nuclei. A complete copy of DNA is found in every cell of the plant. The structure of DNA is long, linear strands. Traits for the plant are coded by genes found along the length of the DNA. In order to analyze DNA, scientists must break open the cells and remove the structural proteins and enzymes that interfere with its structure. This simple lab activity releases a great deal of DNA so that students can see it. Grade Level: Grades 9 ‐ 12 Time Needed: 40 ‐ 60 minutes Learning Objectives: After completing this lesson, students will: 1. Observe that DNA is in the food they eat 2. Be able to perform a simple DNA extraction method 3. Be able to explain why each step in the extraction method is necessary due to the complex organization of DNA in cells As a result of activities in grades 9 ‐ 12, all students should develop: Science as Inquiry 12ASI1: Abilities necessary to do scientific inquiry 12ASI2: Understandings about scientific inquiry Life Science 12CLS1: The cell 12CLS2: Molecular basis of heredity Materials: † Untoasted wheat germ † Detergent solution: Mix 50 mL of liquid dishwashing detergent and 8 grams of sodium chloride with 975 mL of distilled water. † Meat tenderizer containing the enzyme pepsin. Prepare a 6% solution (6 grams per 100 mL of distilled water) The solution will need to be filtered and refrigerated. † Hotplate † Thermometers † Mortars and pestles † Pans for preparing hot water and ice baths † 150 mL beakers † 95% ethanol, chilled † Ice † Cheesecloth † Test tubes † Disposable pipettes † Glass stirring rods Instructional process: 1. Prepare hot water baths and ice baths for use around the classroom. 2. Make copies of the Student Lab Sheet and distribute to students. 3. Verbally “walk through” the steps of the lab activity and explain what is happening at each step. Highlight the need to be precise in all steps of the lab activity. 4. Have students complete the lab activity and answer the discussion questions. Supplemental Content – Explanation of the Extraction Process 1. Measure out 5 grams of untoasted wheat germ. Using a mortar and pestle, grind the wheat germ until it is a fine powder. Place the powder in a 150 mL beaker. What’s Happening: The grinding of the wheat germ with a mortar and pestle breaks the cell walls and releases the cellular content. 2. Mix 100 mL of detergent solution with the ground wheat germ powder. Stir the mixture and heat it between 50‐60 degrees centigrade for ten minutes. Stir the mixture continuously during the process. Do NOT exceed 60 degrees centigrade. What’s Happening: Water in the detergent solution hydrates the DNA and other cellular material. The detergent breaks open the nuclear membrane to release the DNA. The detergent also emulsifies the lipids and proteins within the cells and causes them to precipitate out. The detergent solution also contains a small amount of sodium chloride which reacts with the negative phosphate ends of the DNA and causes the nucleic acids to stick together. Heat denatures the nuclease enzymes, which cut the DNA into smaller pieces, making it hard to collect. 3. Cool the mixture in an ice bath to about 25 degrees centigrade. 4. Filter the mixture through three thicknesses of cheesecloth. Pour the mixture carefully so that the undissolved material at the bottom of the beaker is not transferred. This liquid is known as the filtrate. 5. Place 2 mL of the wheat germ filtrate into a test tube. Add 2 mL of the meat tenderizer solution to the test tube. Gently mix the filtrate and the tenderizer solution. Try to avoid foaming. Let the solution stand for one minute to allow the protease enzyme in the meat tenderizer to react. What’s Happening: Pepsin in the meat tenderizer is a protein‐digesting enzyme. It helps remove extra proteins away from the DNA. 6. Add 2 mL of ice‐cold 95% ethanol by slowly pouring it down the side of the test tube to create a layer on top of the cellular suspension. Let the tube stand undisturbed for a period of one minute. What’s Happening: DNA is not soluble in cold ethanol. Other cell components dissolve. The DNA will precipitate out as a stringy mass. 7. Place a clean glass stirring rod in the boundary between the two layers. Using a circular stirring motion, wind up the DNA. Keep winding until you have an amount of DNA that is large enough to see clearly. 8. What’s Happening: Isolated DNA is a linear, sticky molecule. It will adhere to clean surfaces. Follow Up Questions 1. What did the DNA look like? Relate what you know about the chemical structure of DNA to what you observed today. 2. Explain what happened in the final step when you added ethanol to the cellular suspension. 1. (Hint: DNA is soluble in water, but not in ethanol.) 2. Why is it important for scientists to be able to remove DNA from an organism? List two reasons. 3. Why did the experiment use wheat germ as opposed to the entire grain? 4. Is there DNA in your food? ________ How do you know? DNA Extraction – Student Sheet
Introduction All life functions within a plant are controlled by the genetic material found within its cells’ nuclei. A complete copy of DNA is found in every cell of the plant. The structure of DNA is long linear strands. Traits for the plant are coded by genes found along the length of the DNA. In order to analyze DNA, scientists must break open the cells and remove the structural proteins and enzymes that interfere with its structure. This simple lab activity releases a great deal of DNA so that students can see it. Materials: † 5 grams untoasted wheat germ † Detergent solution † Meat tenderizer containing the enzyme pepsin. Prepare a 6% solution (6 grams per 100 mL of distilled water) The solution will need to be filtered and refrigerated. † Hotplate † Thermometer †
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Mortar and pestle Pans for hot water and ice baths 150 mL beaker 95% ethanol, chilled Ice Cheesecloth Test tube Disposable pipettes Glass stirring rod Procedure: 1. Measure out 5 grams of untoasted wheat germ. Using a mortar and pestle, grind the wheat germ until it is a fine powder. Place the powder in a 150 mL beaker. 2. Mix 100 mL of detergent solution with the ground wheat germ powder. Stir the mixture and heat it between 50‐60 degrees centigrade for ten minutes. Stir the mixture continuously during the process. Do NOT exceed 60 degrees centigrade. 3. Cool the mixture in an ice bath to about 25 degrees centigrade. 4. Filter the mixture through three thicknesses of cheesecloth. Pour the mixture carefully so that the undissolved material at the bottom of the beaker is not transferred. This liquid is known as the filtrate. 5. Place 2 mL of the wheat germ filtrate into a test tube. Add 2 mL of the meat tenderizer solution to the test tube. Gently mix the filtrate and the tenderizer solution. Try to avoid foaming. Let the solution stand for one minute to allow the protease enzyme in the meat tenderizer to react. 6. Add 2 mL of ice‐cold 95% ethanol by slowly pouring it down the side of the test tube to create a layer on top of the cellular suspension. Let the tube stand undisturbed for a period of one minute. 7. Place a clean glass stirring rod in the boundary between the two layers. Using a circular stirring motion, wind up the DNA. Keep winding until you have an amount of DNA that is large enough to see clearly. Follow up questions 1. What did the DNA look like? Relate what you know about the chemical structure of DNA to what you observed today. 2. Explain what happened in the final step when you added ethanol to the cellular suspension. (Hint: DNA is soluble in water, but not in ethanol.) 3. Why is it important for scientists to be able to remove DNA from an organism? List two reasons. 4. Why did the experiment use wheat germ as opposed to the entire grain? 5. Is there DNA in your food? ________ How do you know?