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doi: 10.1242/10.1242/jcs.00067
Book Review |
by Gerald H. Pollack
Ebner and Sons (2001) 305 pages. ISBN
0-9626895-1-3 $27.95
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Ever since seeing a book entitled Why People Believe Weird Things, I've been meaning to sit down and read it. Although I haven't yet gotten around to reading that particular book, I recently read a different book that raises the same question.
Cells, Gels, and the Engines of Life attempts to explain cell biology in terms of gels, discarding virtually all of molecular biology in the process. Cell membranes are the first thing to go. The book starts off by asserting that cells can be cut or punctured without affecting their physiology, implying that membranes do not act as boundaries. This leads to an immediate dismissal of ion channels and pumps. After all, if there is no barrier, there is no need for channels. In order to explain why the cell's contents don't leak out after cutting, the cytoplasm is described as a gel. Electrical and chemiosmotic gradients are proposed to result from selective gel properties.
Unfortunately for this whole argument, cells rapidly reseal their membranes after cutting, through calcium-mediated fusion of cytoplasmic vesicles (e.g. McNeil et al., 2000). If the membrane is not successfully patched, the cell dies. So, actually, the membrane is a barrier after all, and there is no reason at all to doubt the existence of ion channels.
Motivated by these over-interpreted cell-cutting experiments, the book proceeds to force all of cell biology into a Procrustean bed of polymer physics, which leads to some rather unusual proposals. Consider flagellar motility. Conventionally, we assume that dynein arms bend the flagellum to drive the cell through the medium. The book questions this model on first principles: cilia and flagella have circular cross-sections, it is stated, and aren't shaped like paddles as one would expect. Therefore, it is argued, they can't propel cells by beating against the surrounding media. Evidently, in addition to not believing in ion channels, we aren't supposed to believe in mastigonemes either. An alternative model is formulated based on the phenomenon of bead movement. Plastic beads stuck onto the outside of flagella in Chlamydomonas move back and forth at a rate of roughly 2-3 µm/second. Why, the book asks, would flagella have such motility unless it was to power swimming? That this motility might simply mediate gliding on solid substrates is never considered, in spite of the fact that Chlamydomonas lives in the soil and mainly moves by gliding rather than swimming. Instead, surface-bead movement is proposed to be the sole motile force for cellular swimming, and the book speculates that flagellar bending merely points the end of the flagellum in the right direction, so that the fluid flowing off the end can exert force in a given direction, like the rotatable nozzles of a Harrier jump-jet engine. This is a strange model given that bead movement is bi-directional and, thus, unlikely to produce much net flow. Moreover, Chlamydomonas swimming speed has been clocked at around 200 µm/second. It is not obvious how a 2 µm/second flow could propel the whole cell at a speed of 200 µm/second.
The model for flagellar motility is by no means the most startling section of this book. For example, it is asserted that myosin doesn't contract muscles by moving its head domain along actin, but rather by contracting its coiled-coil domain (the head doesn't do anything, apparently). Indeed, our whole concept of motor proteins is challenged on the grounds that motors are so small that they are incapable of pulling their much larger cargo (a cartoon of a frog trying to pull a tank is included to emphasize this point). The implied relationship between a molecule's size and its force-generating capacity is never revealed to us, however, because the book has to move on to bigger issues, such as human diseases. Cancer, for example, is explained as being due to mutant proteins (whose identity is not specified) that act not by influencing the cell cycle machinery (of which there is no mention) but, rather, by somehow causing water to become disordered and thereby somehow promoting mitosis, leading to cell proliferation.
Let's try to be fair. Sometimes cell function really is just a matter of simple physics. There is unquestionably a need for a careful, balanced exploration of the role that simple physical phenomena, such as gels and diffusion, may play in cell biology. I had hoped that Cells, Gels, and the Engines of Life would be such a book, but unfortunately it is not. Apart from the fact that many of the arguments seem, at best, incompletely thought-out, this book obviously has an axe to grind and spends far too much time grinding it. For example, a comparison is drawn again and again between the molecules discovered by modern cell biology and the wheels-within-wheels of Ptolemaic astronomy. Evidently, we are meant to conclude that gel theory has been persecuted just like Galileo was and therefore must be true. The same comparison is also invoked to attack molecular biology on the grounds that it is too complicated to be correct. Although we all may wish, at times, that we didn't have to remember so many darned molecules, that doesn't mean we can just ignore them. We must, with the author, recall Einstein's admonition to make things as simple as possible, but not simpler.
Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, CT, USA
References
McNeil, P. L., Vogel, S. S., Miyake, K. and Terasaki, M. (2002). Patching plasma membrane disruptions with cytoplasmic membrane. J. Cell Sci. 113,1891 -1902.[Abstract]
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