The cell walks over its own engine.

Structure of a Cytoskeleton

Any design for the engine has to account for one fact: the engine is in a constant cycle of decay and rebirth. The cell walks over its own engine, most of which remains stationary, even as the cell creates a new version of the engine at the cell front. The researchers’ new blueprints for the engine have a natural beauty, because the mechanism for constantly recreating the engine is a logical byproduct of the basic motor design.

The motor’s other trick is that it must produce asymmetry where once there was none. Your average cell is like a balloon filled with jelly, but somehow this balloon can transform itself into a movement machine. It’s as if the parts of a car engine, initially strewn across a floor, could grab onto each other and take the car out for a spin. Suddenly the cell has a front that pushes outwards and attaches to its surroundings, a middle that pulls the rest of the cell forwards with a molecular motor, and a back that lets go.

Making a Movement Machine