The baffling intelligence of a single cell (2024)

This explains how a single E. coli cell performs chemotaxis - an elegant, computation-like behavior that lets it hunt nutrients without a brain. The bacterium alternates between straight swims ("runs") and random reorientations ("tumbles") by coordinating multiple flagellar rotors: synchronous rotation bundles tails for a run, asynchronous rotation induces a tumble. A small signaling protein, CheY, is phosphorylated into CheY‑p at a rate set by membrane receptors; CheY‑p binds rotors and increases tumbling. When receptors detect an increasing attractant concentration the phosphorylation flow is interrupted, CheY‑p falls, runs lengthen, and the cell biases its random walk up the gradient. The system amplifies tiny changes - sensing shifts of only a few molecules per cell volume.

Sensitivity across huge concentration ranges comes from receptor methylation: attractant-bound receptors acquire methyl groups that dampen signaling, so the cell treats its recent background as a new baseline. Methylation and demethylation provide a short chemical memory allowing the cell to compare past and present concentrations. The broader network - kinases, phosphatases, methylases and demethylases - implements a constantly cycling, tunable circuit whose fast phosphorylation/dephosphorylation dynamics yield rapid, flexible responses. This motif underlies much cellular computation; understanding the physical details, not just flowcharts of names, reveals how simple chemical mechanisms produce robust, adaptive behavior.