By BBC News Online Science Editor Dr David Whitehouse
June 16, 1999
A large-scale prototype of a computer that could be smaller
than a living cell has been designed by an Israeli
Some scientists believe that, in the future, small
biological computers could roam our bodies monitoring our
health and correcting any problems they may find.
The prototype has been developed by Professor Ehud Shapiro
of the Computer Science Department at the Weizmann Institute
It is being presented at the Fifth International Meeting on
DNA-Based Computers at the Massachusetts Institute of
In terms of the logic on which it operates, the prototype
will behave in a similar way to molecules inside a living
cell, a "biomolecular machine".
A living computer
Each cell of our bodies is a collection of machines made out
of biological molecules. These molecules can form pulleys
and gears to move other molecules around the cell.
Some molecules have the ability to assemble and take apart
other molecules. Others gather small molecules and use a
template to construct new molecules.
In a sense, each of our cells is a complicated city of
biological machines all working together.
It is possible that a future biomolecular version of
Professor Shapiro's device could lead to the construction of
computers, smaller than a single cell, and with the ability
to monitor and modify them.
If scientists were ever able to build such a computer, its
medical applications would be far-reaching. It could swim in
our bloodstream or be attached to specific organs monitoring
and supplementing their performance.
"For example, such a computer could sense anomalous
biochemical changes in the tissue and decide, based on its
program, what drug to synthesise and release in order to
correct the problem," says Professor Shapiro.
A Turing machine
Existing electronic computers are based on the architecture
developed by John von Neumann in the US in the 1940s. But
the new mechanical computer is based on the Turing machine,
conceived in 1936 by the British mathematician Alan Turing.
The Turing machine uses the basic concepts of computing,
reading and writing one bit of data and performing an action
depending upon a program. But although the Turing machine is
a general-purpose, universal, programmable computer and is
key to the theoretical foundations of computer science, it
has not been used in real applications.
Like a Turing machine, Professor Shapiro's mechanical device
has a "rule molecule" designed so that the processing of the
molecule modifies another molecule in a predetermined way.
To demonstrate the concept, Professor Shapiro has built a
30-centimetre-high plastic model of his mechanical computer.
He hopes that the advent of improved techniques for making
and assembling molecules will mean the day when his computer
could be made is not far off.
If it were built from biological molecules it would measure
about 25 millionths of a millimetre in length, roughly the
size of a cell component called a ribosome.
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