Page 124 - The Miracle in the Cell Membrane

(1) (2)
These diagrams show
the entry into the cell of
LDL (low density
lipoprotein) particles
by means of endocyto-
sis. LDL particles build
a covalent bond with
Clathrin
covered 0.2 μm the protein ferritin, and
cavity LDL-ferritin LDL-ferritin then the cell membrane
(3) (4) forms a sac by which
these particles are
absorbed. Under an
electron microscope,
every small iron parti-
cle within the ferritin
can be seen as a small
dot.

from the cell's sur face and in the form of a cap sule, joins
the cell cyto plasm. During this proc ess, cal ci um ions
need to be present in the extra cel lu lar fluid because cal ci -
um allows the pro teins, which per mit the cap sule to sep -
a rate from the cell mem brane, to shrink.
Pinocytosis can be observed con stant ly in most cell
mem branes, although in cer tain cells it may take place
very rap id ly. In macro pha ges, for instance, a total of 3%
of the cell mem brane may be taken into the cell in the
form of sacs in the space of one minute. These sacs used

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