gel electrophoresis – moving DNA through a gel
medium using an electric current
Liquid solutions of the gel is poured into a mould and
allowed to set and solidify.
Why can we move DNA with electricity?
DNA has a negative charge.
Each well is loaded with a different sample of DNA.
Samples often contain multiple pieces of DNA of
The gel provides resistance for DNA movement.
moves through gel easily
travels further in a set amount of time
requires more effort to move through gel
does not move as far in a set amount of time
Describe the DNA fragment lengths that have been
The gel medium can be made from:
1. agarose - seaweed extract
2. polyacrylamide - artificial polymer
The type of gel used is dependent on how well
separated the DNA pieces need to be (resolution).
Polyacrylamide has higher resolution than agarose.
DNA is colourless.
How do you know that it gets into the gel?
Coloured dyes are mixed with DNA to track distance
How do you see where the DNA is after the separation
DNA is stained with ethidium bromide and a UV light
box to see fluorescent DNA bands
How do you know how long your DNA fragments are?
A DNA ladder is also loaded on the gel containing
known lengths of DNA.
Samples of unknown length can then be approximated
through comparison with the DNA ladder.
The ladder is also known as a DNA marker.