Active transport and self-organization in living cells

Efficient control of mass, energy, and information flows is critical for the robust function of large complex systems. Cities, for example, can come to a standstill when power grids, transportation, or information networks are disrupted. A living organism is another - one whose function requires the tandem operation of circulatory and nervous systems that couple disparate parts of the body, orchestrating the joint work of billions of cells. Large-scale coordination is no less essential in a single cell, especially for events leading up to cell division or the maturation of an egg. Much of that coordination is actuated through the cell's cytoskeleton, a collection of polymers, cross-linkers, and molecular motors, that organizes itself into mesoscopic active structures to perform its various tasks. Along this vein, I'll discuss how genetic material is "properly" positioned within the cell as it moves towards division, and how egg cells self-organize large-scale transport flows during growth. Both involve the collective interaction of cytoskeletal polymers with motors, and understanding them has required new experiments, new models, and new methods of simulation. As mechanics problems they are also beautiful, giving rise to novel fluid-structure problems, and new instabilities to ponder.