Is the cell a gel--and why does it matter?

That the cell is a gel is broadly acknowledged. Textbooks begin with this assertion-and then proceed with great abandon to derive mechanisms based on free diffusion, as though the gel concept were groundless and cell was an aqueous solution. This disconnect emerges in part because the behavior of gels is not well understood, particularly among most biologists. Recently, great strides have been made in the understanding of gel behavior. It has become clear, for example, that a central mechanism in gel function is the phase-transition-a qualitative structural change prompted by a subtle change of environment, not unlike the transition from ice to water. Phase-transitions are capable of doing work. If the cell is a gel, then a logical approach to understanding cell function is to understand gel function-especially whether some role may be played by the phase-transition. Here we pursue this approach. We first consider the dichotomy of the cell as a gel and the cell as an aqueous solution. We then set up a gel-based foundation for cell behavior, in which the gels' physical chemical features are used to explore how the cell achieves its everyday tasks. If there is a common underlying mechanism of cell function, it appears that the polymer gel phase-transition could well be a candidate.