Page 224 - The Miracle in the Cell Membrane

To establish an affinity link
between cells, the distance between the
surfaces of the two complementary
adhering molecules must be less than 1
nanometer, and they must be correctly
aligned. It is difficult for these condi-
tions to be met, yet binding still takes
place, even if the links in the cell mem-
brane not approach one another to the
requisite extent. These links are strong
enough to bear a 40-nanogram weight
(1 nanogram = 1 billionth of a gram). If
the affinity links between cells were
not that strong, it would be exceeding-
ly difficult for one cell to bind to any
other.
Many cells can establish bonds to
other cells by means of a single protru-
sion; this can constitute a permanent
bond by means of two affinity links.
Were the affinity links in this bonding
system a few times weaker, the cell
could not attach to another. In addi-
tion, proteins would not be stable, and
enzymes would not bind to the rele-
vant substances. If these links were
stronger, then it would be very hard
for bonded cells to separate from one
another. As you have seen, there is a

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