Electrophoresis Notes

Topics: Agarose gel electrophoresis, Molecular biology, Gel electrophoresis Pages: 3 (702 words) Published: March 28, 2015
What is gel electrophoresis?
Gel electrophoresis is a technique that separates pieces
of DNA (or other biological molecules) by size.
Pieces of DNA in a test tube all
look the same.

DNA Gel Electrophoresis

Gel electrophoresis separates pieces of DNA by size so
that researchers can further analyze them

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November 29, 2005

Once the DNA samples are loaded onto the gel, an electric current is applied to the gel. DNA is negatively charged due to all the phosphate groups in the backbone of DNA. Thus, DNA will move towards the positive electrode.

How does gel electrophoresis work?
First a gel is prepared. Gels are made of agarose, a seaweed extract similar to gelatin. The finished gel has a consistency similar to very firm jello. This consistency offers resistance to the pieces of DNA as they try to move through the gel. The gel is prepared with wells at one end so that DNA samples can be loaded into the gel. 1

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3

4

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- electrode

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direction of migration

Wells for loading samples

- electrode

+
Side View

Side view

+ electrode
Top view

+ electrode
Top View

Top view

As the pieces of DNA move through the gel, they will meet with resistance. Larger pieces of DNA will have more difficulty moving through the gel than smaller fragments. Thus, larger fragments will move slower than smaller fragments. This allows separation of all different sizes of DNA fragments.

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2

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4

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Here you can see the migration of
different fragments of DNA over
time. Lane 2 contains a small
fragment only, lane 3 a large
fragment only, and lane 4 both a
small and a large fragment.

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Larger fragment
Smaller fragment

30 minutes

10 minutes

20 minutes

10 min

20 min

1

Uses of DNA Gel Electrophoresis
Is my DNA still there?
Is my DNA completely cut?

Uses of DNA Gel Electrophoresis
Restriction mapping - where...
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