Page 76 - The Miracle in the Cell Membrane

The Miracle in the Cell Membrane

cell—which itself con sists of 70% water—must be able to
enter and leave. The phos phol i pid mol e cule is cre at ed
espe cial ly for this pur pose. One end of it is hydro phil ic—
that is, it attracts water—while the other end of it (being
hydro pho bic), repels it.
The fatty layer mak ing up the great er part of the cell
mem brane con sists of these spe cial phos phol i pids mol e -
cu les. The phos phate end attracts water mol e cu les and
holds onto them, while the fat end is hydro pho bic. As
this struc ture forms, the hydro phil ic phos phate groups
turn them selves towards water, and the hydro car bon
chain dis tan ces itself from water because of its hydro pho -
bic prop er ty. As a result, the phos phol i pid mol e cu les
string them selves togeth er to form a cell mem brane in
which the hydro phil ic phos phate sec tions face the inner
and outer sur fa ces of the mem brane. To put it anoth er
way, the phos phol i pids bind to one anoth er end-to-end
and form a dou ble-
lay er ed mem brane.
The Water-attracting
Hydrophilic Section The hydro phil ic
ends face both the
water-based cyto -
The Water-repelling
Hydrophobic Section plasm inside the cell
and the liquid
between the other

The water-retaining phosphate parts of the phospholipid molecules
making up the cell membrane face the cell's exterior surface. If the
phosphate sections were inside, then the water-repellent lipid parts
would repel water. Water could not enter the cell, chemical reactions
in the cell could not take place, and its life would be endangered.

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