In affinity chromatography, which statement best describes what happens to the protein of interest?

• A. All proteins bind and stay on the resin.
• B. No interaction occurs and all proteins pass through.
• C. Everything passes through except the protein of interest.
• D. The resin nonspecifically binds many proteins.

Answer: (C)

In affinity chromatography, the resin carries a ligand that binds specifically to the protein of interest. When the sample is applied, most other proteins don’t interact with that ligand and flow through the column, while the protein of interest binds to the resin and is retained. After washing away unbound proteins, the target protein is eluted by changing the conditions (such as pH or salt) to disrupt the interaction. So the description that everything passes through except the protein of interest captures this idea: the protein of interest stays bound on the resin while all other components move through, and then is later released.