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Sodium dodecyl sulfate in SDS-PAGE

Sodium dodecyl sulfate or SDS contains a polar head group with a net negative charge at the end of a long hydrophobic carbon chain. When heating up the sample, SDS binds to the protein, covering it with the negatively charged head groups. This process denatures the proteins, as SDS cleaves the hydrogen bonds, ionic bonds and hydrophobic interactions that hold the protein together in a particular structure. Furthermore, when SDS binds to the protein, it covers the protein with the negatively charged head groups, making the protein negatively charged.

Illustration of a protein before and after the influence of sodium dodecyl sulfate. To the left is an unaffected protein in its regular structure that is held together in a folded formation by hydrogen, ionic and disulphide bonds together with hydrophobic interactions. To the right is the influenced protein in a slightly unfolded structure where all hydrogen bonds, ionic bonds and hydrophobic interactions have been cleaved. Also the protein has been covered in negative charge.

Figure 1. Effect of SDS on a protein: Protein before and after the influence of SDS.

Referred from:

Article
Preparing protein samples for electrophoresis