Gel electrophoresis
Separating molecules by size
and charge
Gel electrophoresis
Image credit: biotechnologyonline.gov.au/
Electrophoresis of DNA
In electrophoresis an electric current is set
up across a watery gel – agarose
 Negatively charged molecules move to the
positive terminal and positively charged
molecules move to the negative terminal
 Each nucleotide on the DNA molecule
carries a negative charge
 Therefore, DNA molecules only move from
the negative cathode to the positive anode

© 2010 Paul Billiet ODWS
Electrophoresis of DNA
Negative charge increases with size, big
DNA molecules move more quickly
 However, bigger molecules move more
slowly through the gel
 The result is a steady and fine separation
of DNA molecules by size
 Molecules which differ by only one
nucleotide in their length can be separated

© 2010 Paul Billiet ODWS
Electrophoresis of DNA
Marker molecule
indicates the front
Agarose Gel
CATHODE Wells for the
mixture
+
ANODE
Buffer solution
DNA fragments separating by size
© 2010 Paul Billiet ODWS
Gel electrophoresis
Image credit: biotechnologyonline.gov.au/