AAMC FL Practice Exam

What technique separates proteins based on their charge?

1. SDS-PAGE

2. Ion-exchange chromatography

3. Size-exclusion chromatography

4. Affinity chromatography

The correct answer is: Ion-exchange chromatography

Ion-exchange chromatography is a technique that separates proteins based on their charge. This method relies on the interaction between charged proteins and charged resin in the chromatography column. Proteins with a net charge will either be attracted to or repelled from the resin, depending on their overall charge at a given pH. The pH and ionic strength of the buffer can be manipulated to optimize the separation, allowing different proteins to elute at different times based on their charge characteristics. In contrast, SDS-PAGE primarily separates proteins based on their size after they have been denatured, while size-exclusion chromatography separates based on the size and shape of the proteins, allowing larger molecules to elute first. Affinity chromatography selectively isolates proteins based on specific interactions with a ligand attached to the resin, not charge. Thus, ion-exchange chromatography is the clear choice for separating proteins according to their charge.