September 17, 2007 at 3:16 pm 2 comments

SDS-PAGE stands for sodium dodecyl (lauryl) sulfate-polyacrylamide gel electrophoresis. It sepearates proteins accroding to their sizes. Therefore, this technique can be used to identify and quantify proteins and to check sample purity.

SDS is a detergent that has a negative charge (from the sulfate) attached to it. It will denature protein samples, leaving the protein in its primary structure, and give it negative charges. This ensure that the protein samples migrate through the gel based on their size alone, not other properites like secondary, tertiary or quarternary structures or electric charges.

Polyacrylamide is a polymer consisting of acrylamide monomers. It forms a gel with “tunnels” of different sizes. When the protein samples are loaded into the gel and placed in an electric field, they will move toward the positive charge (Recall that the SDS has given the proteins negative charges). The smaller proteins will make their way through the gel faster, so the proteins samples are separated based on their sizes. The samples contains many copies of the same protein. They could also be a mixture of proteins, but the proteins with the same size always migrate to the same position in a defined period of time.

SDS-PAGE example  stained gel

The intensity of the bands depends on the amount of protein in the samples. To see individual bands clearly, only a small quantity is required. While running the gel, the proteins are colourless and invisible. The gel needs to be stained to see bands on the gel. Usually, the gel is never run so long that the bands totally migrate to the other side.

This fact that SDS-PAGE only separates proteins according to their sizes deserves a caveat. Different proteins with the same size will move to the same position and end up in the same band. In this case, individual proteins can not be identified.

SDS-PAGE (PolyAcrylamide Gel Electrophoresis)
SDS-PAGE entry in Wikipedia


Entry filed under: Techniques. Tags: , .

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2 Comments Add your own

  • 1. rajesh kumar sharma  |  November 23, 2007 at 3:35 am

    I am workind on wheat quality breeding aspect and so using SDS-PAGE,but unfortunately getting not suitable results.I am countering undermentioned problems:
    1. Not sharp bands of HMW & LMW.
    2. the electrophoresis unit wire which remained immersed in Buffer become black after some time just like carbon deposits in the automobile exaust.
    if anybdy can help in quest
    Rajesh Sharma
    PAU Ludhiana(PUNJAB)

  • 2. Vikas Mishra  |  May 2, 2008 at 9:16 am

    Dear rajesh,

    Check the buffers you have used for making resolving and stacking gels, usually the resolving one should be tris 1.5M having pH of 8.8 where as Stacking should be Tris 1.0 M having pH 6.8. Hope this will work


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