Page 222 - The Miracle in the Cell Membrane

How Does a Cell Select the Cell to Bind
to?

The surface of a typical cell is not smooth, but rough.
Most cells make contact with one another by means of
micro-protrusions on their surfaces known as phyllopods,
which are generally no longer than 0.1 microns in length
and cover no more than 1/100th of a square micron. The
cell uses these micro-protrusions as if they were fingers,
to discover its environment and feel the surfaces of other
nearby cells.
Binding to another cell takes place as a result of spe-
cial molecules on these micro-protrusions. Binding mole-
cules, present in pairs, bind with their mutually comple-
mentary surfaces. Proteins apply the lock-and-key recog-
nition principle they use to recognize substances. The
bond between two binding molecules is known as the
affinity link, whose strength consists of the totality of var-
ious weak chemical bonds that attach two molecules
together.
The external surfaces of cells are negatively charged.
For that reason, cells repel each other electrostatically.
Under these conditions, it would appear impossible for
them to remain in physical contact with one another. But

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