Section: Chemical and Physical Foundations of Biological Systems

31) In an SDS-PAGE procedure, the SDS serves as a detergent. Why are the proteins treated with a detergent before being run through the electrophoresis gel?

1. To coat the proteins with a large positive charge, since amino acid side chains may have positive, negative, or neutral charges, and a large uniform charge is necessary to get good separation in the gel.
2. To allow the electrophoresis to separate the proteins solely on the basis of the length of the primary sequence.
3. To prevent the protein from denaturing so that the electrophoresis can accurately resolve the proteins on the basis of tertiary structure.
4. To break the intramolecular bonds holding the tertiary and primary structure of the protein together, thereby generating linear fragments that may be sorted on size.