Download DNA Extraction Lab

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DNA Extraction Lab
Deoxyribonucleic acid is a molecule, found in the nucleus of cells, that carries the
genetic instructions used in the growth, development, functioning and reproduction of
all known living organisms and many viruses. Most DNA molecules consist of two
biopolymer strands coiled around each other to form a double helix.
Question: What do you think DNA will look like?
Hypothesis:
Materials & Equipment: 2 beakers, test tube, test tube rack, funnel, filter paper,
spoon, strawberry, isopropyl alcohol, zip loc bag, salt, dish soap, goggles, water,
stirrer, forceps, petri dish
Procedure:
A. Creating the Extraction Mixture
1. Measure 90 mL of water into a beaker.
2. Add 10 mL of dish soap to the water.
3. Stir in a ¼ tsp of salt and mix with the stirrer until the salt dissolves.
B. Extracting the DNA
1. Place one strawberry into a zip-loc bag and add the extraction mixture.
2. Remove as much air from the bag as possible and seal it closed.
3. Use your hands and fingers to mash, smash, moosh, the strawberry inside of the
bag. You don’t want any large pieces remaining.
4. Pour the resultant strawberry pulp and extraction mixture through the filter paper
into a beaker. Use a spoon to press the mashed bits of strawberry against the filter
paper forcing even more of the mixture into the beaker.
5. Pour the extraction mixture into a test tube. This will help isolate the DNA on the
surface of the mixture.
6. Add 5 mL of chilled isopropyl alcohol to the solution and hold the mixture at eye
level. You’re looking for a separation of material that shows up as a white layer on the
top. That’s the DNA of the strawberry!
7. Use the tweezers to gently remove the DNA from the solution and lay it on a dish to
examine.
Name ______________________________________
Per. ______
Strawberry DNA
Observations, describe and draw what the DNA looks like below.
The long thick fibers you pull out of the extraction mixture are real strands of
strawberry DNA. As you may know, DNA is present in every cell of all plants and
animals and determines all genetic traits of the individual organism.
While other fruits are soft and just as easy to pulverize, strawberries are the perfect
choice for a DNA extraction lab for two very good reasons: (1) they yield way more
DNA than other fruits, and (2) they are octoploid, meaning that they have eight copies
of each type of DNA chromosome. (Human cells are generally diploid, meaning two
sets of chromosomes.) These special circumstances make strawberry DNA both easy to
extract and to see.
To extract the DNA, each component of the extraction mixture plays a part. Physicall
squishing the fruit breaks down the cell walls. Soap helps to dissolve cell membranes.
Salt is added to release the DNA strands by breaking up protein chains that hold
nucleic acids together. The mixture was filtered to separate out the large cell parts that
not needed. Finally, DNA is not soluble in isopropyl alcohol, especially when the alcohol
is ice cold, so it precipitated out.
Questions
1. Why do strawberries yield way more DNA than other fruits?
2. What does it mean to be diploid?
3. Why do we “crush” the kiwi/strawberry fruit?
4. Why do we use soap?
5. What does the salt do?
6. What does the cold ethanol do?