Homework/2

1. Holy and Leibler (1994) estimate that the time wasted by a microtubule that nucleates in the wrong direction (away from a kinetochore) is, on average, $R/(r\delta)$ where $R$ is the radius of the cell, $r$ is the rate at which monomers both attach and detach at the MT tip and $\delta$ is the size of a monomer. If a MT starts at the cell centre with a single monomer and turns around whenever it reaches the cell boundary, derive the estimate above using the theory for a diffusing particle discussed in class.
2. Using the formalism discussed in class (see slides), calculate the net force generated by a MT aster in which motors pull on all MTs along their entire length rather than just at the tip. Is the center a stable steady state for the aster?