Home

Gel electrophoresis to visualise DNA

Today in the lab I was doing some genotyping to determine which DNA samples contained a specific mutation. To do that, I first run a PCR reaction to obtain some fragments of DNA for the gene of interest. I then had to do gel electrophoresis with these DNA fragments to visualise them. This technique helps me identify the samples with the genotype I am looking for.

Timelapse: loading the DNA samples into a gel tank for gel electrophoresis.

What is gel electrophresis and how does it work?

Electrophoresis is the movement of a charged particle in an electrical current. Gel electrophoresis is a technique that separates DNA, RNA and protein molecules based on their size and charge.

This technique uses a gel (in the video above I am using an agarose gel that I prepared) as an anticonvective medium during electrophoresis.

During gel electrophoresis, an electric current is applied to move the charged molecules through the gel. Gels suppress the thermal convection caused by the application of the electric current.

The electric field generated consists of a negative charge at one end which pushes the molecules through the gel, and a positive charge at the other end that pulls the molecules through the gel.

DNA is negatively charged, and therefore it will be repelled by the negative charge whereas it will be attracted towards the positive charge.

Shorter molecules move faster and migrate farther than longer ones because shorter molecules migrate more easily through the pores of the gel.

The DNA samples are run alongside a DNA ladder which contains fragments of different known sizes, so that we can compare the samples to the ladder and figure out their size.

Gel electrophoresis in progress. Each tiny well was loaded with a DNA sample previously amplified by PCR. The purple bands are an indication of how far down the gel the samples have run.
Gel electrophoresis in progress. Each tiny well was loaded with a DNA sample previously amplified by PCR. The purple bands are an indication of how far down the gel the samples have run.