Working with DNA
Country: United States
Date: July 2005
How do scientists manipulate DNA? I mean we are talking
about chromosomes, which are far too tiny to be visible to the naked eye,
and can only be seen using electron microscopes. It is easy to say that
scientists chop off this or that chromosome from the spiral, but what do
they use to do that? Obviously they can't use a scalpel! Do they use
You're right, there is no way to physically manipulate DNA. It is all done
chemically using enzymes like reverse transcriptase, polymerase chain
reaction (pcr) and restriction enzymes. Reverse transcriptase makes DNA
copies of RNA, pcr makes multiple copies of a particular gene and
restriction enzymes cut DNA at specific locations or nujcleotide sequences
in a DNA molecule. These reactions are all carried out in vitro without ever
seeing a DNA molecule.
Ron Baker, Ph.D.
Actually, it is easy to extract DNA from cells. You have about 3 feet (!)
of DNA in EACH of your trillion cells. So scraping some cells from the
inside of your cheek and getting enough DNA to study is not difficult.
First, you have to break the cell membrane and then the nuclear membrane.
This can be done with detergents and heat. The DNA is soluble in water, but
not alcohol, so if you add alcohol to this mixture, the DNA will just float
above the alcohol and can be wound around a stick. Also, you can see this
mass of DNA with the naked eye because there is so much there. But it isn't
possible to see one single DNA molecule, because all molecules are too small
to see, even with an electron microscope. So to manipulate the DNA once it
is out of the cells, scientists use certain enzymes called restriction
enzymes to "cut" the DNA into small pieces that are easier to work with.
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Update: June 2012