Gel electrophoresis is a laboratory technique used to separate DNA fragments, RNA, or proteins based on their mass and charge. It is a key method used in:

• Genetic fingerprinting
• Gene sequencing
• Forensics
• Disease diagnostics
• Protein analysis

How Gel Electrophoresis Works (DNA)

Step-by-Step:

1. DNA is cut into fragments using restriction endonucleases (restriction enzymes).
2. These DNA fragments are loaded into wells in a slab of agarose gel.
3. An electric current is applied across the gel.
4. Because DNA is negatively charged, it moves towards the positive electrode (anode).
5. The gel acts as a sieve:

• • Smaller fragments move faster and further.
  • Larger fragments move more slowly and travel less distance.

The separated fragments can be visualised by staining the DNA with a loading dye prior to putting the DNA into the wells. (otherwise DNA would not be visible).

The DNA can also be visualised by adding fluorescently labelled probes that bind to the DNA after separation and then using UV light to visualise them.

• DNA fragments of different lengths will migrate through the gel at different rates.
• DNA fragments with a greater number of base pairs will have a longer length and therefore a greater mass.
• These fragments would not travel as far in the gel compared to DNA fragments with a smaller mass.
• This separation based on mass creates distinct bands, where each band represents a fragment of a particular size.

• A DNA ladder is where DNA fragments of a known length are separated on the gel alongside samples of unknown length.
• The fragments of unknown length can be compared to the fragments of the DNA ladder to estimate their length by comparison.

Yes - but the process is slightly different:

• Polyacrylamide gel (not agarose) is often used for higher resolution.
• The proteins will be separated by mass, but this depends on the number of amino acids in the polypeptide chains.
• They are also separated by charge, but this depends on the amino acid R-groups they contain.