Biology Reference
In-Depth Information
FIGURE 14.23
Left: Joseph Goldstein (1940
e
); Right: Michael Brown (1941
e
)
[64]
.
and ions through to large macromolecules and, for phagocytosis, even whole cells. Pinocy-
tosis is Greek for 'cell drinking' and involves the plasma membrane invaginating a volume
of extra-cellular fluid and anything it contains including water, salts, biochemicals, and even
soluble macromolecules. Phagocytosis is Greek for 'cell eating' and involves the plasma
membrane invaginating large insoluble solids.
Pinocytosis
Pinocytosis is a form of endocytosis involving fluids containing small solutes. In humans
this process occurs in cells lining the small intestine and is used primarily for absorption of
fat droplets. In endocytosis the cell plasma membrane extends and folds around desired
extra-cellular material forming a pouch that pinches off creating an internalized vesicle
(
Figure 14.24
,
[52]
). The invaginated pinocytosis vesicles are much smaller than those
generated by phagocytosis. The vesicles eventually fuse with the lysosome whereupon
the vesicle contents are digested. Pinocytosis involves a considerable investment of cellular
energy in the form of ATP and so is many thousand times less efficient than receptor-
mediated endocytosis. Also, in sharp contrast to RME, pinocytosis is non-specific for the
substances it accumulates. Pinocytosis is not a recent discovery but was first observed
decades before the other transport systems discussed above. Its discovery is attributed to
Warren Lewis in 1929.
