TOP SECRET DNA EXTRACTION Motivation: Give a visual sense of DNA. Note to teacher: This manual guides you on how to carry on a discussion by asking questions, giving information and presenting fun facts. Students are then asked to conduct the experiment by following the step by step procedure and fill out the pre-experiment, during experiment, and post experiment worksheet. Class Discussion (Duration: ~ 20 min): Engage the class by asking: Why do we look like our parents? We look like our parents because of Deoxyribonucleic acid (DNA) and the genes we share. Who looks more like her dad? Who looks more like her mom? DNA is the blueprint or recipe of life. It dictates whether something becomes plant or animal, what it looks like, how it is to survive, and how it will interact with its surrounding environment. Friedrich Miescher discovered DNA in 1869, although scientists did not understand DNA was the genetic material in cells until 1943. What sorts of things have DNA? All living things have DNA, including plants, animals, bacteria, etc. Is DNA found in all living or once living cells? Yes, DNA is present in all living and once living cells. Scientists can use DNA from mummies or seeds that are thousands of years old and identify the genetics of those plants and animals using their DNA. Fun fact: Did you know that on average, we share 90% of our DNA with each other, 80% with a dog, and 50% with a cabbage! Where do living cells store their DNA? DNA is inside every cell of each living organism. Specifically, it is inside the cell nucleus. What does DNA look like? DNA is a double helix, spiral shaped that contains the genes. The genes are bound strongly together as a double helix ladder shape structure. DNA is composed of four
nucleotides: adenine (A), guanine (G), thymine (T), and cytosine (C). Combination of these nucleotides dictate your skin color, your eye color, etc. Fun fact: Did you know that DNA could stretch from earth to sun back, 600 times! In order to study DNA, we have to first get it out But, why do scientists want to extract DNA? Once we extract it, what is it good for? To change DNA. For instance, they can change a crop DNA to make it resistant to certain pests or insects. To analyze DNA. Some diseases are linked to differences in DNA and therefore, scientists can find what genes are responsible for that disease. To identify people. Each person’s DNA is unique and therefore, one can identify criminals from the DNA left in the crime scene. In this experiment, we are planning to extract DNA from a fruit. In order to extract the DNA, we have to do some physical and chemical actions. Steps involve breaking the cells to release the DNA, then we have to separate DNAs from the cell debris. As you do experiment, please think about why we do each step and how does it help us in extracting the DNA. Procedure (Duration: ~ 30 min) First we need to prepare a solution to break the cells and release the membrane 1. Transfer the salt into the “water” falcon tube and shake gently until salt is dissolved. 2. Put the falcon tube aside. 3. Get the zip lock and put your fruit in (⅓ of banana)
4. Smash the fruit gently until it becomes soft (Why? to separate the cells and to break down the cell wall, cellular and nuclear membrane.)
5. Transfer the salt-water solution into the ziplock
6. Gently mash until you make a soft paste 7. Place the paper filter on the plastic cup, open your ziplock bag and pour the fruit mash through the filter into the plastic cup. You can gently squeeze the filter (Note: Remind students not to squeeze too hard to avoid getting solid particles out or tear the filter)
8. Once the liquid has passed through the filter and collected in the plastic cup, discard the filter paper. 9. Tranfer 20ml of this liquid to the â€œResultsâ€? falcon tube 10. Add a drop or two of a hand soap and gently stir (Note: Why soap? Cells have a layer of membrane around them which is composed of lipid. As we get oily stains off of plates using dishwashing soap, we can break (lyse) the cell and nucleus membrane using this hand soap)
11. Hold the “Results” falcon tube in one hand, tilt to 45 degrees, and pour 20 ml of alcohol on top from the “Alcohol” falcon tube. (Note: how does the salt water and alcohol help in isolation of DNA from cell debris? Na+ ions (sodium) neutralize the negative charges on the DNA molecules, which makes them more stable and less water soluble. Next, alcohol (such as ethanol or isopropanol) is added and causes the DNA to precipitate out of the aqueous solution because it is not soluble in alcohol.)
12. Close the cap and wait for 2-3 minutes 13. Observe the DNA strands and fragments; they are like cotton strands floating on the solution.
EXAMPLE WORKSHEET Pre-experiment Worksheet:
What differentiates your appearance from your friend? Genes in DNA are different from one person to another and that makes us different from our friends in terms of eye color, skin color, height …
What is DNA? How does it look like? DNA is a chain of nucleotides carrying genetic information. DNA is in the form of double-helix and comprised of four nucleotides: Adenine (A), Guanine (G), Thymine (T), and Cytosine (C). Is DNA found in all living or once living cells? Yes, DNA is present in all living and once living cells. Scientists can use DNA from mummies or seeds that are thousands of years old and identify the genetics of those plants and animals using their DNA. What is the purpose of isolating DNA? To change DNA. For instance, they can change a crop DNA to make it resistant to certain pests or insects. To analyze DNA. Some diseases are linked to differences in DNA and therefore, scientists can find what genes are responsible for that disease. To identify people. Each personâ€™s DNA is unique and therefore, one can identify criminals from the DNA left in the crime scene. During the experiment:
What is the purpose of smashing the fruit? To break down the cell wall, cellular and nuclear membranes. What is the purpose of adding soap? The soap dissolves the cell and nuclear membranes that protect the DNA. How come we can not see the DNA until we add alcohol to the solution?
The DNA is still dissolved in the solution. We need the alcohol to bring it out. After the experiment:
What did DNA look like? The DNA look like a white, thin fibers wadded up together forming a clump. Do you think you would have seen a difference if you would have chosen a fruit? Appearance wise, the DNA in all fruits look like a white, thin fibers wadded up together forming a clump, but the genes are obviously different. Do you think we could isolate our own DNA this easily? Yes, encourage students to research about isolating DNA from their own cheek cells.