Gel Electrophoresis

Gel Electrophoresis Overview

Used to separate mixtures of DNA, RNA, or proteins according to molecular size.
The DNA sample is pushed by an electrical field through a gel that contains a matrix of small pores.
An electric current is applied across the gel so that one end of the gel has a positive charge and the other end has a negative charge.
Charged molecules migrate towards the opposite charge. DNA, which has a negative charge, will therefore be pulled towards the positive end .
Smaller DNA molecules migrate through the gel more quickly and travel further than larger fragments that migrate more slowly and travel a shorter distance. Thusly, the molecules are separated by size.

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The use of dyes, fluorescent tags or radioactive labels enables the DNA on the gel to be visualised after they have been separated. They will appear as bands on the gel.
A DNA marker with fragments of known lengths is usually run through the gel at the same time as the samples.
By comparing the bands of the DNA samples with those from the DNA marker, you can work out the approximate length of the DNA fragments in the samples.

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The electrohoresis gel is very fragile and so, before the DNA seperation can be properly visualised, the DNA must be transferred to a more durable medium
A nylon membrane is laid on top of the gel and a blotting paper is laid over the membrane
Through capillary action, the buffer solution surrounding the gel is drawn onto the membrane along with the DNA

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