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PARTISAN REVIEW
logical circuit, or "genetic applet," would possess data processing and
storage circuitry as well as the input/ output components necessary for
sensing and affecting its environment.
Before biological integrated circuits become a reality, several techni–
cal challenges must be overcome. In particular, more efficient and scal–
able methods are needed for fabricating long sequences of DNA.
Currently, fragments of DNA must be copied, cut, and pasted from pre–
existing fragments to piece together a complete synthetic network, a
process that can take weeks even to insert a single gene. This process is
akin to writing an essay by cutting and pasting words from a photo–
copied magazine article. Although it is currently feasible to synthesize a
sequence of DNA from scratch, it is economically impractical, costing
several thousands or tens of thousands of dollars for a single synthetic
gene. In addition, current technologies cannot efficiently integrate more
than five to ten genetic elements at a time.
Another technical challenge is the "wiring problem." In a biological
circuit, signals are carried by molecules that uniquely recognize and
affect the activity of another molecule. For example, the regulator pro–
teins in the genetic flip-flop bind to specific sequences in the DNA and
thereby inhibit protein synthesis. Each element in a biological circuit
must be a unique biochemical signal that interacts only with the
intended elements and no others. Currently, no method exists for effi–
ciently generating thousands of novel and unique biochemical signals.
However, recent research on the engineering of special DNA binding
proteins suggests a possible solution to at least one aspect of the wiring
problem .
The DNA fabrication and wiring problems are just two of several
technical challenges that remain in the path of practical biological cir–
cuits. But with the accelerating pace of basic biological research and
industrial genomics efforts, solutions to these problems may not be far
in the future.
If
increasingly complex biological circuits are developed
with a pace anything like that of electronic integrated circuits, they may
have an extraordinary impact on our lives.
Biological circuits, however, are not likely to replace the functions of
electronic circuits . More likely, they will fill needs that electronic circuits
cannot, such as the precise control of biochemical events at the cellular
level. Ultimately, genetic applets might be "downloaded" into a cell, cre–
ating, in effect, a "wet" nanorobot. These cellular robots might scav–
enge toxins from the bloodstream, autonomously synthesize complex
three-dimensional chemical matrixes, repair complicated genetic disor–
ders in animals and humans, control the growth of synthetic organs, or
