What type of samples does SDS-PAGE separate?

SDS-PAGE, or sodium dodecyl sulfate-polyacrylamide gel electrophoresis, is a technique specifically designed to separate proteins based on their molecular weight. The method works by denaturing proteins and coating them with a negative charge through the binding of SDS, allowing them to be separated as they migrate through a polyacrylamide gel in an electric field. Since the proteins are linearized and given a uniform charge-to-mass ratio, the migration speed through the gel primarily depends on their size; smaller proteins travel further through the gel than larger ones.

Other options, such as nucleic acids or circular DNA, are processed with different gel electrophoresis methods, such as agarose gel electrophoresis. Similarly, small organic compounds do not typically undergo separation via SDS-PAGE, which is specifically tailored for protein analysis. Thus, the focus of SDS-PAGE on protein separation by molecular weight is what makes it the correct answer in this context.