Engineering - Molecular Theory of the Living Cell - page 116

Chapter 5
Engineering
5.1 Microelectronics
5.1.1 Enzymes as “Soft-State” Nanotransistors
Molecular and cell biologists may benefit conceptually from a generalized notion of
the transistor , an abbreviated combination of “transconductance” and “resistance,”
that includes any physical device that can activate a physicochemical process when
energized. Given such a generalization, we can readily recognize two distinct
classes of transistors - (1) artificial transistors made out of solid-state materials
and (2) natural transistors, that is, enzymes, made out of deformable (or soft )
heteropolymers of amino acids, namely, proteins and polypeptides.
Solid-state transistors conduct electricity when energized by applied voltage,
while soft-state transistors enable or cause chemical reactions to occur when
energized by substrate binding (Ji 2006e; Jencks 1975). Just as transistors are the
basic building blocks of the digital computer, so enzymes are the basic building
blocks of the living cell, the smallest molecular computer in Nature (Ji 1999a). This
provides a theoretical framework for comparing the properties of and the physical
principles underlying solid-state transistors and enzymes (see Table 5.1 ). A similar
table was discussed in NECSI Discussion Forum (Ji 2006e).
The content of Table 5.1 is mostly self-explanatory, but the following items
deserve special attention:
1. Process . The process enabled by a solid-state transistor when energized is the
flow of electrons through it. In contrast, the process enabled by an enzyme when
energized is the flow of electrons from one atomic grouping to another within a
given molecule (most often a substrate) or from one molecule to another (Row 1).
2. Size . The linear dimension of the cell is at least 10 3 times smaller than that of the
digital computer, and this is reflected in the physical dimension of enzymes
relative to that of typical transistors (see Row 2).