TOSSING COINS INSIDE LIVING CELLS

Our immune cells protect us by eating up bacteria. Once eaten, bacteria are transported to an execution chamber by the "Motor" proteins Kinesin and Dynein. These nanoscale motors generate force in opposite directions, and the balance of these forces guides the bacteria to its death. Pathogenic bacteria survive by upsetting this balance to make you sick. 

We use Optical trapping to directly measure the force, and therefore the activity of Kinesin and Dynein in real-time on bacteria. We show that the choice between Kinesin and Dynein is described by tossing a hypothetical coin (a stochastic Markov process). A binomial probability calculation based on the geometry explains this process, revealing a physical basis for the spatial organisation of components inside living cells.