Biology Reference
In-Depth Information
merical models of macromolecules.
7
Atomic positions within the pro-
teins were stored as vectors within the computer, so that (to quote from
Levinthal's paper again) “the illusion of rotation and, consequently a
three-dimensionality, can be produced by presenting the observer with a
sequence of projections of an incrementally rotated vector model.” The
visual display and the means of manipulating it provided protein mod-
elers with a means of “seeing” numbers stored within the computer in
a way that had biological meaning. Indeed, the main use of the models
was, as Levinthal put it, to “assist in the process of user directed modi-
fi cation of structure.” In other words, users would manually alter the
confi guration of the protein on their screen in order to refi ne the struc-
ture or to simulate protein folding. The computer did not automatically
calculate the optimum confi guration of the protein, but rather allowed
the user to experimentally tweak the model until a satisfactory represen-
tation was found. Levinthal's work was an attempt not just to represent
biological macromolecules inside computers, but to allow biologists to
do something with the representations in order to learn about the func-
tion and behavior of proteins.
Despite Levinthal's efforts with protein structures in the 1960s,
computer-based visualization in biology did not catch on. As Francoeur
and Segal argue, the advantage of Levinthal's technology over ordinary
physical modeling were not immediately obvious to biochemists, who
had their own research styles (Levinthal himself was a nuclear physicist
by training, not a biologist), and the cost of setting up the computing
equipment was prohibitively high. It is also signifi cant that Levinthal
and his colleagues reported their work not to a conference of biologists
or biochemists, but to a group of computer graphics specialists. Reports
on the use of computers in biomedicine in the 1960s, such as the Air
Force-commissioned
Use of Computers in Biology and Medicine
from
1965, saw the main prospects of computing in data storage and quan-
titation, mentioning imaging hardly at all.
8
This was no doubt in large
part because most computers of the 1960s were not powerful enough
to process images at all—many were still working by means of punched
cards.
As biologists began to deal with larger and larger amounts of data,
“visual” thinking proved increasingly useful, even if it was not directly
associated with computing. Margaret Dayhoff's work on protein se-
quences, discussed in detail in chapter 5, was organized around the con-
cept of an “atlas.”
9
Dayhoff's
Atlas
looks nothing like an atlas of maps,
nor much like the anatomical or botanical atlases of the eighteenth and
nineteenth century. However, it has in common with other atlases the
