Hierarchical organization of the plasma membrane: Investigations by single‐molecule tracking vs. fluorescence correlation spectroscopy

Single‐molecule tracking and fluorescence correlation spectroscopy (FCS) applied to the plasma membrane in living cells have allowed a number of unprecedented observations, thus fostering a new basic understanding of molecular diffusion, interaction, and signal transduction in the plasma membrane. It is becoming clear that the plasma membrane is a heterogeneous entity, containing diverse structures on nano‐meso‐scales (2–200 nm) with a variety of lifetimes, where certain membrane molecules stay together for limited durations. Molecular interactions occur in the time‐dependent inhomogeneous two‐dimensional liquid of the plasma membrane, which might be a key for plasma membrane functions.