What key aspect is measured during the FRAP technique?

The Fluorescence Recovery After Photobleaching (FRAP) technique is designed to measure the mobility of molecules within a membrane. In this method, a specific area of a fluorescently labeled membrane protein is photobleached using a high-intensity laser. After the bleaching, the recovery of fluorescence in that area is monitored over time. The extent to which fluorescence returns indicates how readily other, unbleached fluorescently labeled molecules move into the bleached zone.

This mobility is essential for understanding various biological processes, such as protein diffusion, protein-protein interactions, and membrane dynamics. By analyzing the recovery curve and calculating parameters like diffusion coefficients, researchers can gather valuable insights into the behavior of proteins and lipids in a membrane environment. Therefore, this technique specifically focuses on the mobility of molecules, making it a critical tool in cell biology and biochemistry. Other options do not pertain to the core aspect measured by this technique.