Download Human Cheek Cell DNA Extraction

Human Cheek Cell DNA Extraction
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Introduction
DNA – the seemingly mysterious substance that holds the secrets of life, turns out to be a relatively
simple chemical polymer made of repeating patterns of A’s, T’s, C’s, & G’s (representing the
chemicals Adenine, Thymine, Cytosine, & Guanine). How can something so simple be the very stuff of
life itself, the instruction booklet for life, a how-to guide for building a living thing? In the course of
the next few weeks we will uncover the basic process by which DNA gets things done. In the meantime,
this lab will further de-mystify DNA by allowing you to see it for your own eyes as a rather abundant
substance found in virtually all of your body’s cells.
How it works: The cell itself and again the nucleus within the cell are both surrounded by membranes
made primarily of phospholipids. Detergent, by emulsifying lipids in water, destroys the membranes
and thereby exposes the contents of the cell & nucleus, including the DNA.
Saltwater helps remove cells from your cheeks and also makes the watery solution denser – this
increased density will facilitate the separation of the DNA strands into the alcohol.
Alcohol is less dense than water so it floats on top of the water. Most of the cellular components are
“heavy” (dense) enough to remain in the watery solution at the bottom of the test tube. DNA, however,
is less dense than either the water or the alcohol, so it floats to the surface of the alcohol. DNA is also
soluble in water but “precipitates” (separates, more or less) in alcohol.
DNA is exceedingly thin (0.0000002 mm!) but clumps together. This is similar to the idea that cells are
microscopically small (invisible to the naked eye) but “clumped” together in a multi-cellular organism,
are quite visible without the need for a microscope.
Purpose
To use a protocol for extracting DNA from cheek cells
To observe a collection of DNA strands
Materials
Scupala or Spoon
Paper clip or Wooden Stick
2 paper cups or glass beaker
120mL distilled or bottled water
1/4 tsp salt
1 tsp baking soda
1 tsp of detergent
1 drop pineapple juice
1 oz 90% isopropyl alcohol (chilled in freezer
beforehand)
Safety/Precautions
Do not handle anyone’s materials except your own.
Immediately dispose of paper cups
Do not ingest (eat or drink) any materials used in this lab except water supplied.
Procedures
This extraction works best if students have not just recently eaten or chewed gum.
1. Take the two paper cups and one beaker and label one then spit cup (beaker), one the buffer solution
(paper cup), and the second paper cup the water a salt solution (2nd paper cup).
ST
Buffer Solution (2-4)- ONLY FOR 1
PAPER CUP ONLY
2. Add the distilled or bottled or distilled water to your paper cup. (Tap water contains impurities that can
damage extracted DNA.)
3. Use the spoon to stir in the salt and baking soda until they've completely dissolved in the water. The salt
will prevent your DNA from bunching together before it has separated from surrounding proteins, and the
baking soda will give the solution a neutral pH.
4. Mix in a teaspoon of detergent and just a drop of pineapple juice. The soap will break down your cells and
liberate your DNA, while the juice destroys the proteins surrounding it.
Spit BEAKER (5)
5. In the second paper cup mix a small amount of water and salt.
6. (USE THE MIXTURE FROM 6)Take a small amount of water—not your buffer solution—and slosh it around in
your mouth for about 30 seconds. Then spit into the spit BEAKER. You now have a fresh collection of cheek
cells from which you can harvest your DNA.
7. Pour some of the buffer solution into the BEAKER containing your saliva. You should add about twice as
much buffer as you have spit and water.
8. Stir gently. You should now have a soup of DNA, broken cells, and proteins all mixed together.
9. Gently pour the isopropyl alcohol down the side of the cup so that it sits on top of the mixture. This should
be straightforward, because alcohol is less dense and therefore lighter than your buffer solution and saliva.
10. Let the mixture stand for two minutes. You will soon see strands of DNA floating up toward the alcohol.
11. Remove the DNA from the solution by unbending your paper clip to look like a hook and then gently
swirling it around the alcohol to collect the strands, which gathered together will resemble a translucent
slime.
Remove the clip and voila! You've just successfully extracted your own DNA. Although a single strand is too small
to be seen by the naked eye, you can see your DNA here because you've collected a lot of it from a large number
of cells. When the strands left the cheek cells, they intertwined into larger, more visible masses.
Analysis Questions
1. What is DNA?
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2. What does your DNA “look” like?
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3. Why doesn’t your DNA look like the double helix we see in textbooks?
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4. Where is DNA Found?
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5. What is the role of detergent in the DNA extraction lab?
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See also the following resources for DNA extraction:
How to extract DNA from Anything: http://learn.genetics.utah.edu/units/activities/extraction/
Nova: Cracking the Code of Life: http://www.pbs.org/wgbh/nova/teachers/activities/2809_genome.html
Access Excellence (Advanced): http://www.accessexcellence.org/AE/AEC/CC/DNA_extractions.html