Miss SB
01/14/09
DNA Extraction
A. Purpose:
The objective of this experiment is to break down split peas and view their DNA
macroscopically. After various agents dissolve and break down the outside of
the pea's cells, protein-coated clumps of macroscopic DNA will become visible.
Even though the DNA in a cell's nucleus is too small to be seen with the naked
eye, this experiment provides a way to view macroscopic DNA. This gives
observers a clear idea of what DNA looks like on a macroscopic scale.
DNA is the basis of all life. Its structure follows a double-helix shape,
consisting of two backbones containing phosphorus, oxygen, carbon, and
hydrogen. The two halves of DNA are held together by nucleotide base pairs.
There are four types of nucleotide bases: adenine, thymine, guanine, and
cytosine. When they link together to connect the two halves of the DNA, only
adenine and thymine can link together, and only guanine and cytosine can link
together. Because of these limits on which bases can bond with each other, DNA
can easily replicate itself accurately. (CHEMystery)
DNA is an incredibly efficient way to store the massive amounts of information
needed by a living body. A sample of DNA the size of a pinhead can hold the
same amount of information as a stack of books reaching 500 times higher than
the distance from the earth to the moon. Adding this to the fact that, if all
the DNA in one human's cells were unwound, it would reach the moon 6,000 times
over (Rothamsted), demonstrates the incomprehensible amount of information
stored in the body by DNA. Some of this DNA tells cells what functions to
perform to continue life, while some of this DNA controls a person's genetics
and those of their children. The study of this incredible structure continues
to reveal more and more information about the mystery of life. Although the DNA
described here is too small to observe with the naked eye, it will be studied
on a macroscopic scale during this experiment.
This experiment hopes to show how to extract and observe DNA on a macroscopic
scale. Certain steps must be taken to extract DNA from a cell. After that, a
scientist must know what to look for and where to look for it in examining the
DNA. This experiment will demonstrate both the process of extraction and the
details of observation.
This experiment is of interest to science because, although DNA is an
absolutely critical element for life and the continuation of life, it has been
discovered quite recently. Therefore, compared to sciences like physics, which
have been studied for thousands of years, relatively little is known about DNA.
The mysteries of DNA that scientists face today can be solved only by careful
study of DNA itself. This experiment, therefore, teaches about and allows
observation of DNA in a way that could lead to new discoveries about this
amazing facet of life.
Hypothesis: If substances with certain properties are effectively added
to split pea cells in the right order to break down the cell, then the pea's
DNA will be extracted and become visible to the naked eye.
B. Equipment:
1. Blender
2. Toothpick
3. Clear liquid hand soap
4. Salt
5. Water
6. Strainer
7. Small glass
8. Meat tenderizer (Make sure it has
been bought within the last year or so.)
9. Rubbing alcohol
10. ½ cup of split peas
11. Measuring cups and spoons (1 cup,
1/4 teaspoon, 1 tablespoon)
12. Flashlight
13. Plastic bowl (although the text
includes this in the equipment list, it is never mentioned in the experiment
and is not necessary for successful completion of the experiment)
C. Procedures:
1. Dissolve ¼ teaspoon salt in one cup
of water.
2. Place the peas and salt water into
the blender and blend for 20-30 seconds. The result should have the consistency
of thin pea soup.
3. Hold the strainer over the small
glass and slowly pour the contents of the blender into the strainer, allowing
the liquid to drip into the small glass.
4. Add two tablespoons of the soap to
the solution in the glass.
5. Slowly mix the liquid and the soap by
swirling, and then let it sit for at least 10 minutes.
6. Add ¼ teaspoon of meat tenderizer and
mix very gently.
7. Slowly add as much rubbing alcohol as
there is liquid. Do not stir! The alcohol will sit on top of the liquid. Wait
for a few minutes, and white strands should appear in the layer of alcohol.
8. To aid in seeing the strands, shine
the flashlight down onto the surface of the solution and look at the solution
from the side of the glass.
9. If the strands are long enough, twist
them onto a toothpick and remove them from the solution.
10. Clean up the mess.
D. Observations:
All of the materials for the experiment were gathered before the experiment was
begun. When salt was added to the water, the clear water became slightly
cloudy. After the peas and saltwater were put in the blender, they were mixed
on "blend" setting. The blender roared very loudly at first because
the peas were dry. Once the whole mixture became liquid, the blender worked
more quietly. As soon as the peas began to be blended, they emitted a strong
smell like fresh peas. After the suggested blending time, the remains of the
peas settled to the bottom while the now-green salt water sat on top of them.
In an attempt to mix them more thoroughly, the blender was run for another ten
or fifteen seconds. The peas still settled to the bottom. An inch-high layer of
green-tinted froth sat on top of the water. When the mixture was poured into
the strainer, the green water and froth flowed into the glass while the thick
remains of the peas stayed in the strainer. The soap formed globs when it was
dumped into the glass, but after some gentle swirling it disappeared. After the
mixture sat for about fifteen minutes, it felt significantly more thick when
stirred. The rubbing alcohol did not mix at all with the pea mixture when it
was added, but instead sat on top of the liquid, turning a shade of green that
was lighter than the rest of the pea mixture. Almost immediately the alcohol
fogged up and very large semi-transparent white strands formed just above the
surface of the pea mixture. There was too much foam on the top to pull out any
of the strands, so a spoon was used to spoon out some of the froth. The size of
the strands exceeded expectations, but they broke apart easily.
E. Conclusions:
The hypothesis stated "If substances with certain properties are
effectively added to split pea cells in the right order to break down the cell,
then the pea's DNA will be extracted and become visible to the naked eye."
This hypothesis was supported by the results of the experiment. When the cells
of split peas were taken and mixed with hand soap, the soap destroyed the
cell's plasma membranes and opened the interior of the cells. After this, when
meat tenderizer was added, it destroyed the protein coat on the cell's DNA.
When the rubbing alcohol was added and formed a new layer of liquid, the
macroscopic DNA appeared in this layer. It was clearly visible to the naked
eye. This proves that when certain substances are used to systematically
destroy the outside of a cell, DNA can be extracted and viewed macroscopically.
This experiment could be improved in several ways. First, the experiment instructions
gave little idea as to what the experiment was supposed to look like after each
step. Because of this, those who perform the experiment cannot be sure if they
are achieving the right results. For example, while the experiment instructions
gave the impression that all of the blended split pea/water mixture was to be
sifted easily into the glass, in reality; the split peas were mainly sifted
out, leaving water mixed with invisible pea cells. In this case the experiment
did not give a clear idea of what to expect. Secondly, the experiment never
provided an explanation of what macroscopic DNA truly is as compared to
microscopic DNA. An explanation at the level of the student would have been
very helpful in analyzing the experiment. The experiment itself could be
improved by finding different ways to study the extracted DNA-either with the
eyes or with a microscope.
This experiment could be used to launch a study on DNA, including extracting
DNA strands from different cells than just pea cells and comparing them.
Different materials could be used to extract the DNA, leading to a study of
what ingredients are necessary to break down a cell. DNA could also be studied
on a microscopic level. This could include its structure, its functions, or
other information. This experiment opens the door to a critical area of life
science.
F. Bibliography:
Castells-Brooke, Nathalie. Rothamsted Research's Molecular Biology Notebook.
Structure of DNA. 2004.
Domain: http://www.rothamsted.ac.uk
Document:
/notebook/courses/guide/dnast.htm
CHEMystery: An Interactive Guide to Chemistry. Organic Chemistry: Nucleic
Acids. 1996.
Domain: http://library.thinkquest.org
Document: /3659/orgchem/nucleicacids.html?tqskip1=1&tqtime=1112
Rosenoff, Steven. Classroom
Lecture. December 12, 2008.
Wile, Dr. Jay. L. and Durnell, Marilyn F. Exploring Creation with
Biology, 2nd Ed. Apologia Educational Ministries, Inc. 2008