Why is SDS used in protein gel electrophoresis?

Gel electrophoresis is a laboratory technique that is used to separate charged DNA, RNA, and protein molecules based on their size. The first step in this process involves denaturing the proteins that will undergo electrophoresis. 

SDS (sodium dodecyl sulfate) is a strong detergent. When used in protein gel electrophoresis, SDS breaks up the cell membranes, solubilizes proteins, and coats them with negative charges. 

Many membrane proteins cannot be run on a protein gel as they are naturally insoluble in water and aggregate. However, the SDS-coated membrane proteins acquire a charge and are soluble in water. This allows them to be easily separated by a protein gel on applying an electrical current.