  Intracellular components explore the cytoplasm via active motor-driven
transport in conjunction with passive diffusion. We model the motion of
organelles in narrow tubular cells using analytical techniques and numerical
simulations to study the efficiency of different transport modes in achieving
various cellular objectives. Our model describes length and time scales over
which each transport mode dominates organelle motion, along with various
metrics to quantify exploration of intracellular space. For organelles that
search for a specific target, we obtain the average capture time for given
transport parameters and show that diffusion and active motion contribute
comparably to target capture in the biologically relevant regime. Because many
organelles have been found to tether to microtubules when not engaged in active
motion, we study the interplay between immobilization due to tethering and
increased probability of active transport. We derive parameter-dependent
conditions under which tethering enhances long range transport and improves the
target capture time. These results shed light on the optimization of
intracellular transport machinery and provide experimentally testable
predictions for the effects of transport regulation mechanisms such as
tethering.
