DNA Extraction Lab

Purpose:  DNA is present in all living organisms.  The purpose of this lab is to extract DNA (get DNA) out of cells so that we can see it.

Materials:  cups, spoon, knife, filter, kiwi, detergent, water, salt, pipette, test tube, ethanol, lab

Procedure:  You must check off each step as you do it!

• Take a cup, put one spoonful of detergent and 2 pinches of salt inside the cup.
• Add water until the cup is 1/3 full.
• Stir slowly for one minute so that the cup does not foam.
• Scoop out seeds from kiwi.  Place the remaining pieces of kiwi in the cup.
• Push the kiwi against the side of the cup with the back of the spoon for 10 minutes.
• Put the coffee filter inside the other cup and fold the edges of the coffee filter down so that the filter does not touch the bottom of the cup.
• Slowly pour the kiwi into the filter and wait until the kiwi solution drains through.
• Get a test tube with cold alcohol.
• Fill the pipette with the kiwi solution and add it to the alcohol.
• Let the solution sit without mixing or shaking it for 3 minutes.  You should see little white pieces of DNA floating out of the solution.
• Stick a probe into the solution and pull out the DNA; it will look like white string.
• Look at the DNA you pulled out underneath the microscope.

Questions:  Do these while you mix up the kiwi solution (10 minutes).

1.  What is DNA?

2.  What four nucleotides make up DNA?

3.  What are the three parts of a nucleotide?

4.  How many chains of nucleotides make up a DNA model?

5.  Read the paragraph below and then answer the questions related to it:

-Extract means to get something out of something else.  Today we are extracting DNA, which means we are pulling DNA out of cells.  To pull DNA out of cells, we must first separate the DNA from the rest of the cell.  As you know, DNA is found in the nucleus.  In order to break down the plasma membrane and open up the nucleus, we add detergent which breaks down the membranes by breaking apart the lipids that make up the membranes.  We then add salt, which allows the DNA to separate from the rest of the cell.

                        A.  What does extract mean?

B.    What do we need to do to get DNA out of the cells?

C.   Why do we add detergent and salt to the kiwi cells?

D.   How does the detergent break down the plasma membrane?

Questions:  Do these while you wait for the DNA to come out of the solution (3 minutes).

1.  Read the paragraph below and answer the questions related to it:

The kiwi mixture was added to the cold alcohol to separate the DNA from the rest of the cell.  When alcohol is added to the kiwi mixture, everything else is heavy and stays in the bottom of the mixture.  The DNA is lighter, so it floats to the top of the alcohol mixture.  You should see little pieces of white string which are the DNA.

                        A.  Why do we add alcohol to the kiwi mixture?

B.    Why does the DNA separate when added to the alcohol?

C.   Why do you think you’re not supposed to shake the test tube while the DNA is separating?

Results:

1. Did your experiment succeed, that is, were you able to pull DNA out of your mixture?

2. Draw a picture of what the DNA looks like with just your eye, with low power under the microscope, and with high power under the microscope.

Conclusion:

1. Look at the structure of DNA below and answer the questions that relate to it.

1. What is the structure of DNA called?

2. What makes up the rungs of the DNA ladder?

3. What makes up the sides of the DNA ladder?

4. How do the nucleotides attach to each other on the sides of the ladder?

5. How do the nucleotides attach to each other on the rungs of the ladder?

6. What bonds hold the nucleotides together?