NAME ____________________________
LAB
PROTOCOL for DNA EXTRACTION from BANANAS
(Adapted by Joslin from Dr. Theresa Fulton’s Original Protocol)
http://www.igd.cornell.edu/StudentHandout.pdf
MATERIALS
Each Station

Three 5 oz. cups, plastic spoon, #2 coffee cone filter, test tube, wood splint, 20 mls cold
distilled water, 20 mls cold alcohol (rubbing alcohol)
Shared Items

Blender, bananas, liquid dish detergent, salt (NaCl)
METHODS
1. In a blender, mix a ratio of 1 banana to 1 cup (250 mls) of distilled water. Blend for 15-20
seconds until completely mixed.
2. In a 5 oz. cup, make a solution of 1 teaspoon of liquid dish detergent and 2 pinches of salt.
Add 20 mls of COLD distilled water. Dissolve the salt and detergent by slowly stirring with
the plastic spoon. Try not to make too many bubbles.
3. Add 3 heaping teaspoons of the banana mixture to the detergent solution. Mix with the
plastic spoon (slowly) and let sit on the lab table for 10 minutes.
 The detergent dissolves the lipids that hold the cell/nuclear membranes together.
This releases the DNA into the solution. The detergent causes lipids & proteins to
precipitate out of solution, leaving DNA. The salt enables the DNA strands to come
together. The "cold" ensures that the DNA will not break down too quickly.
4. Place a #2 coffee cone filter inside a clean 5 oz. cup. Fold the coffee filter edge around the
cup so that the filter doesn’t touch the bottom.
5. Strain the mixture by pouring it into the filter and letting the solution drain for several
minutes. Add this mixture to a clean test tube.
6. Obtain a test tube of about 20 mls of cold alcohol.
7. Gently pour the cold alcohol at an angle into the test tube with the banana mixture. The goal
here is to have the alcohol STAY ON TOP of the mixture with as little mixing as possible.
 DNA is NOT soluble in the alcohol. This is because DNA is polar while alcohol is
nonpolar. Polar & nonpolar do not mix. When the alcohol is added to the mixture, the
components of the mixture – except the DNA – stay in solution. DNA precipitates out.
8. Let the solution sit for 2-3 minutes without touching it. Then, tilt the tube back & forth to
see the DNA strands precipitate. You may spool (scoop up) the DNA with a wood splint by
slowly rotating it in one direction. DNA has the appearance of white stringy mucus.
RESULTS

SKETCH the resulting test tube & the contents inside. Label the following:
 DNA precipitate, alcohol, banana mixture
DISCUSSION
1. List the function(s) of the following chemicals in this lab:
 DETERGENT
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- SALT
---------------------------------------------------------------------------------------------------------------------------- ALCOHOL
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------2. Where was the DNA located inside the banana cells?
---------------------------------------------------------------------------------------------------------------------------------3. Describe 2 functions of DNA?
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4. The subunits (building blocks) that make up DNA are called nucleotides. What 3 parts make
up a single DNA nucleotide? (pg. 192)
-------------------------------------------------------------------------------------------------------5. What are the 4 nitrogen bases found in DNA?
(pg. 193)
-------------------------------------------------------------------------------------------------------6. DNA is often described as a double helix. Two single strands of a DNA molecule are held
together by weak hydrogen bonds that exist between complementary nitrogen bases. What
are the RULES that govern these base-pairings in DNA? (pg. 195)
--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------7. If the sequence of nitrogen bases on one strand of a DNA molecule is CCATGGTAGCGACTT,
what is the sequence of nitrogen bases on the other strand? Use the rules for base-pairing.
-------------------------------------------------------------------------------------------------------8. Whether a cell is about to undergo mitosis OR meiosis, DNA is replicated prior to the cell's
division. Recall that this replication occurs during interphase. What are the steps involved
in DNA replication. Please be specific here! (pgs. 196-197)
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------9. How are ERRORS in DNA replication USUALLY avoided?
(pg. 197)
-------------------------------------------------------------------------------------------------------10. What is a replication fork? What is the major advantage for eukaryotic cells in having
numerous replication forks? (pg. 198)
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