Which technique allows the observation of protein size after separation?

SDS-PAGE (Sodium Dodecyl Sulfate-Polyacrylamide Gel Electrophoresis) is a widely used technique for separating proteins based on their size. In this method, proteins are denatured and coated with SDS, an anionic detergent that imparts a negative charge to the protein molecules. As the proteins migrate through a polyacrylamide gel during electrophoresis, the gel acts as a molecular sieve, allowing smaller proteins to move faster than larger ones.

The resulting separation enables the assessment of protein size by comparing the migration distance of the proteins to a set of molecular weight markers, known as standards, that are run alongside the samples. Therefore, the size of each protein can be estimated based on where it falls relative to these markers on the gel. This technique is essential in biochemistry for analyzing protein purity, estimating molecular weights, and preparing samples for further analysis or downstream applications.

Other techniques listed, such as clearance analysis, affinity chromatography, and mass spectrometry, serve different purposes in protein studies, such as analyzing binding interactions, purifying proteins, or determining molecular weights through mass measurement, but they are not specifically designed for observing protein size after separation like SDS-PAGE is.