Page 228 - The Miracle in the Cell Membrane

The Miracle in the Cell Membrane

cells to form the complex protrusions that let them feel
their way, and it would be impossible for the cell to per-
form vital functions such as bonding and crawling.
Dr. Juliet Lee of the Connecticut University
Molecular and Cell Biology Department made the fol-
lowing comment about the cell's ability to move in the
wake of her research published in Nature magazine:

A lot of people don't realize that many cells are not stationary
but can travel from one place to another. . . If cells could not
move, none of us would exist. Embryos would not develop,
wounds would never heal... When cells are stretched, such as
when they're going forward and their back end gets stuck, cal-
cium channels along the sides open to admit more calcium
ions. This boosts the cell's motility so that the back end is
pulled away from whatever it's been stuck on, and it can move
forward again. . . We also found that if we prevented cells
from exhibiting these pulses of calcium, the cells became stuck
so they could no longer pull their back edges in. . . . As soon
as the rear of the cell retracts, stretching is released, the calci-
um channels close and the level of calcium drops back. 72
The cell's abilities to selectively bind and to crawl
depend on the features of its cytoplasm and the structure
of the cell membrane. Cytoplasm has a most plastic and
mobile structure, ideally suited to crawling and binding.
The cell's abilities to move and bind are possible only
when cytoplasm possesses exactly the proper character-
istics. DNA, protein, sugar and lipids—the basic com-
pounds of life—also possess exactly the right structure
and need to be present in the right proportions for the

226