Name: Date:
DNA Extraction Lab
Problem Statement: Do different organisms contain the same amount of DNA?
In this lab you will compare the amount of DNA in strawberries and bananas. You will begin by predicting which fruit will contain the most DNA.
Prediction:
Procedure:
1. Place your fruit in a zip-lock bag, press the air out, and then seal it. Softly mash the fruit with your fingers until it becomes a juice puree. (1-2 minutes)
2. Add 8 mL of buffer solution to the bag with the fruit, remove air, reseal and carefully mix for 1 minute. NOTE: You do NOT want to create bubbles.
3. Open your bag and add a pinch of meat tenderizer (enzymes), mix carefully.
4. Filter the fruit mixture by setting up a funnel, mesh filter and test tube to collect the filtrate. Stop collecting filtrate when your test tube is ¼ full of juice.
5. Tilt the test tube and pour in an equal amount of alcohol, ¼ of test tube. Let the alcohol run down the side of the test tube so it forms a layer on top of the fruit filtrate. Alcohol is less dense than water, so it will float on top. Do NOT mix! Allow the test tube to rest for 2-3 minutes.
6. Using a stirring rod or wood splint, collect the DNA at the boundary of the alcohol and filtrate. Gently remove the stirring rod and examine what the DNA looks like. Clean up using the teacher’s instructions.
Data:
Draw the DNA you see in your test tube and also in the test tube of a group using a different fruit in the diagram below.
The Science behind the procedure:
Detergent
eNzymes (meat tenderizer)
Alcohol
Why did I add detergent?
To get the DNA out of cells you need to break open both the cell membranes and the nuclear membranes. Cell membranes and nuclear membranes consist primarily of lipids. Dishwashing detergent, like all soaps, breaks up clumps of lipids. This is why you use detergents to remove fats.
Why did I add enzymes?
The nucleus of each of your cells contains multiple long strands of DNA with all the instructions to make your entire body. If you stretched out the DNA found in one of your cells, it would be 2-3 meters long. To fit all of this DNA inside a tiny cell nucleus, the DNA is wrapped tightly around proteins. The enzyme in meat tenderizer is a protease, which is an enzyme that cuts proteins into small pieces. As this enzyme cuts up the proteins, the DNA will unwind and separate from the proteins.
Why did I add alcohol?
The cold alcohol reduces the solubility of DNA. When cold alcohol is poured on top of the solution, the DNA precipitates out into the alcohol layer, while the lipids and proteins stay in the solution.
Questions:
1. What was the manipulated variable in this lab?
2. Was your prediction correct? How did the amount of DNA compare in the various fruits tested?
3. Where is DNA located in the cell?
4. What is the soap buffer breaking down in the cell?
5. Why were enzymes necessary?
6. What did the alcohol do?
7. Which part of the DNA molecule contains the genetic code?
8. Which part of a nucleotide makes a banana and strawberry different?
9. Most of the fruit and vegetables today have been genetically modified. Scientists can cut out a gene from one organism and place that gene into another organism. Give 3 benefits of genetically engineering food plants: