ABSTRACT

Dynamics in cells comes in a number of different forms. One of the most important classes of dynamical process is diffusion, the random jiggling of individual molecules in solution. When many such molecules are diffusing simultaneously, the overall concentration field undergoes changes in space and time that give the appearance of ordered and directed movements of molecules down concentration gradients. Brownian motion is an inevitable outcome of the thermal jiggling of water molecules and does not indicate the activities of a living system. However, diffusive motion is always present at molecular length scales, and biological systems must tolerate, exploit, or inhibit Brownian motion in order to perform directed dynamic processes. There are a number of different techniques that permit the investigation of diffusive dynamics within cells. A more direct technique for monitoring diffusive dynamics is through explicit particle tracking in which individual trajectories are monitored.