What is the primary purpose of SDS-PAGE?

The primary purpose of SDS-PAGE is to separate proteins by size and charge. SDS-PAGE stands for sodium dodecyl sulfate-polyacrylamide gel electrophoresis, which is a technique widely used in biochemistry and molecular biology to analyze proteins.

In this method, proteins are denatured and coated with sodium dodecyl sulfate (SDS), a detergent that imparts a negative charge to the proteins. This allows the proteins to be separated primarily based on their size when an electric current is applied during electrophoresis. Smaller proteins migrate more quickly through the polyacrylamide gel compared to larger proteins, facilitating separation and allowing for estimation of their molecular weight.

This process is crucial for various applications, including protein characterization, purity analysis, and as a preparatory step for further techniques such as Western blotting. The other options provided do not pertain to the main function of SDS-PAGE; for example, amplifying DNA sequences is the goal of techniques like PCR, while staining DNA fragments is a step in gel electrophoresis techniques focused on nucleic acids, not proteins. Visualizing protein structures usually involves different methods such as X-ray crystallography or NMR spectroscopy rather than SDS-PAGE alone.