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RNA is being studied in order to better understand gene expression patterns in cells. Because enzymes
that break down RNA are abundant in nature, RNA is naturally very unstable. Some are even secreted by our
own skin and are extremely difficult to destroy.
RNA extraction,
like DNA extraction,
requires the use of
various buffers and enzymes to inactivate other macromolecules while preserving only the RNA.
Gel Electrophoresis
An electric field can move nucleic acids because they are negatively charged ions at neutral or alkaline
pH in an aqueous environment.
Gel electrophoresis
is a technique used to separate charged molecules on the
basis of size and charge. Nucleic acids can be separated into whole chromosomes or fragments. An electric
current is applied after the nucleic acids are loaded into a slot at one end of a gel matrix, and negatively charged
molecules are pulled toward the opposite end of the gel (the end with the positive electrode). Smaller molecules
move faster through the pores in the gel than larger molecules; this difference in migration rate separates the
fragments based on size. The nucleic acids in a gel matrix are invisible until they are stained
with a compound
that allows them to be seen, such as a dye. Distinct nucleic acid fragments appear as bands at specific distances
from the top of the gel (the negative electrode end) based on their size (Figure 51). A long
smear is formed by
a mixture of many fragments of varying sizes, whereas uncut genomic DNA is usually too large to run through
the gel and forms a single large band at the top of the gel.
Figure 51.
Six samples' DNA fragments
were run on a gel, stained with a fluorescent dye, and viewed under
UV light. (credit: modification
of work by James Jacob, Tompkins Cortland Community College)
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