If SDS PAGE sounds like a ridiculous combination of letters, you urgently need to decipher what these letter mean and understand the mechanism of this technique.
As with all forms of gel electrophoresis, molecules may be run in their native state, preserving the molecules’ higher-order structure, or a chemical denaturant may be added to remove this structure and turn the molecule into an unstructured linear chain whose mobility depends only on its length and mass-to-charge ratio. For nucleic acids, urea is the most commonly used denaturant. For proteins, sodium dodecyl sulfate (SDS) is an anionic detergent applied to protein sample to linearize proteins and to impart a negative charge to linearized proteins. This procedure is called SDS-PAGE. In most proteins, the binding of SDS to the polypeptide chain imparts an even distribution of charge per unit mass, thereby resulting in a fractionation by approximate size during electrophoresis. Proteins that have a greater hydrophobic content, for instance many membrane proteins, and those that interact with surfactants in their native environment, are intrinsically harder to treat accurately using this method, due to the greater variability in the ratio of bound SDS.
Firstly, watch the video.
Then flick through the notes.
A good tutorial about gel electrophoresis can be found HERE.
Big thanks to http://web.mnstate.edu/provost/BiochemistryLabI.html and http://en.wikipedia.org/wiki/Polyacrylamide_gel_electrophoresis.