In a sense, a simple bacterium is like a soap bubble. Both consist of a fluid enveloped by a thin layer of another fluid. But poke a hole in each structure, and their resemblance ends: The soap bubble pops; the bacterium’s single cell reseals. The origin of this difference lies in the competition between surface tension and its lesser-known one-dimensional analog, line tension.
Line tension arises when molecules have to rearrange themselves at the edge of a hole. The rearrangement has an energy cost, which the molecules pay by forcing the edge to shorten. Because a small fraction of molecules bear the cost, line tension is nearly always feeble. In a soap bubble, surface tension prevails. But in a cell membrane, which feels the same pressure inside and out, line tension is the stronger force.
There are reasons to suspect that line tension plays a role in how cell...
