Download DNAExtract05

Extracting DNA from
Eukaryotic Cells
Background
DNA stores and transmits genetic information
Where is DNA located?
In the nucleus of Eukaryotic cells
What cells are we using?
Plant cells from strawberries and
animal cell from a calf thymus gland
Background
Why thymus gland and where is it located?
Thymus acts as an endocrine gland as part of your
immune system. Responsible for teaching “T” cells
to recognize foreign invaders.
Thymus cells have very large nuclei and thus are
rich in DNA.
1. (I) Breaking Down the Tissue
Thymus
Strawberries
Crushing releases the
cells into solution. The
tissues lose their
2. (II) Breaking Open the Cell Membranes and Nuclei
Cell Membrane
Structure
The extraction buffer (soap
and salt) causes the forces
that hold the cell and
nuclear membranes
together to break down.
This “clouds” the mixture.
Positive (+) ions from the
salt neutralize the
negatively (-) charged
phosphate group so that
DNA is no longer soluble.
The DNA can coil upon
itself and begin to
precipitate (“un-dissolve”).
Salt ion
(Na +)
(-)
Nucleotide
3. (III) Collecting the DNA
DNA is soluble in
water but not ethanol.
Addition of ethanol
allows DNA to further
precipitate out (“undissolve”).
The ethanol is less
dense than water and
the DNA is less dense
then ethanol, so the
“snotty” DNA rises to
the surface.
4. DNA is clear when wet (soluable in water), but
sticks and coils in the presence of salt and
ethanol (insoluable in those).
5. Procedures for plant and animal very similar.
Animal cells require sand during crushing b/c
tissue is tougher.
6. ALL human cells contain DNA. Extracted DNA
can be used for analysis, cloning, and
recombination. These applications can cure
disease, produce better food crops, and more
(though there are ethical issues).
Final Note
Every diploid cell in the human body contains about
3 billion base pairs (bp) of DNA in 46 chromosomes.
This is known as the “human genome.”
At actual stretched-out size, a single human cell's
DNA is about 3 meters in length.
The total length of DNA present in ALL the cells of
one adult human (about 10 trillion cells) is the
equivalent to the distance from the earth to the sun
and back.
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