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Protein gel electrophoresis

Protein gel electrophoresis is a technique to separate proteins by size. In the sample preparation, proteins are denatured and a negative charge is added to them by the SDS. The denaturation removes the folding and turns all proteins into linear molecules. The negative charge means that the proteins migrate from the negative pole (cathode) at the top of the gel towards the positive pole (anode) at the bottom. The gel functions like a molecular sieve. Small proteins migrate more easily through it than large proteins. Therefore, small proteins cover a larger distance during the experiment run time and will be found towards the bottom of the gel.

Gel electrophoresis results presented as pink bands spread throughout the gel. The first column on the right with 6 bands stretching from the top to the bottom of the gel is titled the marker, also known as the ladder. The rest of the columns with few bands in each column represent the samples. The pink bands are marked as separated protein fragments, their positions in the gel can be compared to the ladder to determine their size.

Figure 1: A completed gel electrophoresis experiment with 5 samples and the protein ladder on the right. The protein ladder can be used to estimate the sizes of the bands in the samples.

After electrophoresis, the different proteins in the sample will appear as bands at specific distances from the top of the gel on the basis of their size. The sizes of the protein bands can be estimated by comparing the distance with the molecular weight standard samples (also called a ladder).