Geisler: Science 9: 2015
BANANA DNA EXPERIMENT
NAME________________________________________________PD______DATE_____________
**You will be turning in this worksheet for a lab report grade. Since we are in the process of writing a
research paper you will not have to write a lab report for this lab. YOU WILL TURN IN ONE LAB SHEET
PER PERSON.
Purpose: Is to extract DNA from banana cells.
Background: DNA isolation is a process of purification of DNA from a sample using a combination of
physical and chemical methods. The first isolation of DNA was done in 1869 by Friedrich Miescher.
Currently it is a routine procedure in molecular biology or forensic analyses. It is done by breaking the
cells open, commonly referred to as cell disruption or cell lysis, to expose the DNA within. This is
commonly done by grinding or pulverizing, then the membrane lipids are removed by adding a detergent,
then the DNA is taken out of solution by the addition of an alcohol to dehydrate it.
Procedure:
1. Obtain a banana sample.
2. Using a mortar and pestle smash the banana for about 2 minutes, or until the banana is nice and
mushy.
3. Next place banana in beaker.
4. Add 20 mL of extraction buffer and mix.
5. Prepare coffee filter and funnel. (fold coffee filter in half twice, then open it up into a cone shape).
Place filter in funnel.
6. Obtain an Erlenmeyer flask and place the funnel in it.
7. Pour the solution into the funnel to filter out the cell material
8. Wait about five minutes until all the filtrate (liquid that has filtered) has been collected in the flask.
(While waiting answer the following questions, use handout and computer to answer)
Questions:
1. What scientist was the first to extract DNA from cells?
2. What does cell lysis mean?
3. What are two reasons why DNA would be isolated from cells?
9. Pour filtrate into a test tube. (make sure you have a test tube holder as well)
10. Add 1 mL of detergent (dish soap) to the filtrate. Gently mix, without causing foam.
11. Add 20 mL of ice cold ethanol to the test tube by slowly pouring it down the side of the test tube
to create a layer on top of the filtrate. (DNA is not soluble in ice cold ethanol. When it is added to
the mixture, all the components of the mixture except DNA, stay in solution, while the DNA
precipitates out.)
Geisler: Science 9: 2015
12. Let the ethanol sit for 2-3 minutes without disturbing it. (Place test tube in test tube holder during
this time) Bubbles will form and DNA will precipitate out of the solution at the interface (top layer
of solution is the interface).
13. Gently swirl the DNA using a stirring rod. It will look like whitish mucous.
14. The DNA may be lifted out carefully and dried on a paper towel.
15. Examine the DNA, then answer the following questions. EVERYONE NEEDS TO TURN IN A COPY
OF THIS LAB.
Questions:
4. What does the DNA look like?
5. What was the purpose of the mashing up the banana?
6. what does the extraction buffer do? (you may have to research)
7. What does the filter do?
8. What happened when you added the detergent to the filtrate?
9. What happened when you added the filtrate to the alcohol?
10. A person cannot see a single cotton thread four classrooms away. But if you wound thousands of
threads together into a rope, it would be visible at he same distance. How is this statement an analogy
to our DNA extraction?
11. Is DNA found in all living or once living cells?
Geisler: Science 9: 2015