Information Technology Reference
In-Depth Information
Figure 5.2
Information transport through an individual genetic regulatory circuit.
The representation of the information is initially coded in the concentration of small
molecules. During processing the format of this representation changes several times
with the result ultimately represented by the concentration or activity of a protein.
represented by voltages and currents and is communicated through the con-
trolled transport of electrons. In contrast, information in cellular systems is
represented by molecular concentrations and is communicated through the
transport of these molecules and control of molecular production by genetic
expression. As information is transported through cells, the manner in which it
is represented changes several times (Figure 5.2), in contrast to silicon systems
where the information always remains coded within a collection of electrons.
Transistors are the fundamental building block for silicon information-
processing devices. These three-terminal components control current flow
between two terminals using the voltage on the third terminal (Figure 5.3a). Hi-
ratsuka and co-workers [51, 52] have proposed the realization of transistor-like
circuits and interconnections using enzyme-catalyzed reactions and diffusion
of the products.
Hiratsuka et al.'s proposed fundamental device is roughly analogous to a
bipolar junction transistor with current flow represented by the enzymatic con-
version of a substrate into a product as controlled by effectors (Figure 5.3b).
These investigators propose to create complex functionality by coupling mul-
tiple enzyme transistors to form a network of biochemical reactions defined by
the molecular selectivity of enzyme transistors. Information would be coded
into molecular agents and then discriminated by the selectivity of enzyme tran-
sistors. In this plan, information is transported from point to point by molecular
diffusion. Because different molecules represent individual quanta of informa-
tion, there is no need for insulation between interconnect paths. This is an in-
creasingly difficult and ultimately limiting problem for silicon systems at higher
