A GLIMPSE OF 
In the three centuries since Robert 
Hooke turned his microscope on bits 
of dried cork, much has been learned 
about the world inside the cell. 
Directed by the genes and influenced 
by the environment, cells perform an 
astonishing array of tasks and take on 
a variety of forms suited to their work. 
Cell biologists now know a great deal 
about how the cell's living machinery 
works to make proteins, how many of 
the organelles are formed, and the 
steps involved in cell division. With 
so much revealed, it may seem that 
there is little mystery left in cells. But 
this is far from true. 
Large portions of the cell's mem- 
branes, for example, remain un- 
charted territory. Although strides 
have been made in discerning the 
structure, function, and location of 
many surface and inner membrane 
proteins, studies of membrane lipids 
have lagged behind. In the years 
ahead, scientists will be attempting 
to discover how lipids in animal cells 
(which are manufactured at a single 
site, the endoplasmic reticulum) are 
transported to multiple sites through- 
out the cell. 
Studies of cell organelles have 
been intense in recent decades, but 
much still remains to be learned 
about, for example, the actions of the 
Golgi apparatus and the endoplasmic 
reticulum. Protein receptors and 
trafficking signals that direct newly 
made proteins through these organ- 
elles have been postulated, but 
scientists have yet to isolate and 
characterize these systems. New 
techniques will probably be devised 
for examining the roles of cellular com- 
ponents, but there is still a place for 
such time-honored methods as cell 
fractionation, which was used by Paul 
Lazarow of The Rockefeller University 
and other investigators to separate per- 
oxisomes from other cell components, 
thus fueling renewed interest in the 
study of this organelle. 
In the future, isolated studies of cell 
organelles and molecules will be 
increasingly supplemented by investi- 
gations that aim to probe more global 
cellular functions. According to 
Norton Gilula of the Research Institute 
of Scripps Clinic, "the greatest single 
challenge in cell biology today is 
learning what regulates cell division 
and differentiation." How, for example, 
does each cell in a developing organ- 
ism "know" when to turn the appropri- 
ate genes "on" or "off"? Why do 
some cells become "specialists," while 
others remain "generalists"? Why do 
normal cells eventually wear out and 
die — and what factors hasten or slow 
cell death? 
To answer such questions, says 
Gilula, "we need to know not only 
details of shape and action for individ- 
ual molecules, but also how these 
molecules interact in complete cells." 
Because the fundamental unit of an 
organism is the cell, whatever is 
learned about individual genes, pro- 
teins, and other molecules must be 
reinterpreted at the cellular level before, 
a full understanding of the role of each 
in health and disease is possible. 
Already, basic research on how cel Is 
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