Think the memory card in your camera
is high-capacity? It's got nothing on DNA. With data… Read…
The dawn of biological computers is
at hand. In a major first for synthetic biology, Stanford engineers have used
genetic material to create a biological transistor. Called the
"transcriptor," the creation is the final, missing component
necessary for the creation of a biological computer that could enable
researchers to program functions into living cells.
Modern computers rely on three
standard functions. One: they must be able to store information. Two: they have
to be able to transmit information. Three: they need a basic system of
logic – a set of rules that governs how they should function given one or more
forms of input. A biological computer would implement all three on a cellular
level, using proteins and DNA in place of silicon chips.
The first two functions have been
demonstrated with cellular materials before. Several labs have now demonstrated
the ability to store digital data in DNA, some of them at jaw-dropping densities;
and last year, a team led by Stanford bioengineer Drew Endy developed a system
for transmitting genetic information between cells. Now, in a study recounted
in the latest issue of Science, Endy's team
has developed what it calls a "transcriptor" – the biological
equivalent of a digital transistor – and with it a system of logic that can
control cellular function.
In your standard computer,
transistors govern the flow of electricity by playing red light/green light
with electrons along a circuit. Similarly, a transcriptor regulates the flow of
a protein called RNA polymerase along a strand of DNA. Transistors and
transcriptors are, at their most basic, on/off switches – the gatekeepers of
information transmission, storage, amplification, and so forth.
The rules that these gatekeepers
follow give rise to the logic systems that dictate what problems a computer can
solve. A transcriptor gatekeeper that lives by a code of "AND," for
example, might allow RNA polymerase to continue along a strand of DNA when two
predetermined conditions are "true" – if, for example, the
transcriptor detects the presence of Enzyme-A AND Enzyme-B inside the
cell.
A transcriptor that abides by the
code of "OR," on the other hand, would allow RNA polymerase to
continue when either or both of the enzymes are present. In computer
science, transistors that abide by AND-/NAND-/OR-/XOR-/NOR-/XNOR-rules (which you can read all about here) are called
Boolean logic gates. Endy calls his transcriptor equivalents Boolean Integrase
Logic gates. Or "BIL" gates, for short. Below, Endy
provides an in-depth explanation of Transcriptors and BIL gates.
Here's the takeaway: if you line a
bunch of these logic gates up, you form a logic circuit. Get enough logic
circuits together, and you have a computer that can handle just about any
computation you throw at it – whether it's addition and subtraction on a
calculator, or gene expression inside a cell.
Endy plans on starting small. For
now, he's working with bacteria, helping other researchers use his BIL gates to
engineer E. coli that can be programmed to change color. And in a
refreshingly practical take on the potential applications of his team's
creation, Endy told NPR's Morning Edition
that he doubts these DNA computers will ever outwit your iPhone; but this, he
said, is missing the point.
"We're building computers that
will operate in a place where your cellphone isn't going to work."
Endy's team's research is published
in the latest issue of Science. For a
fantastic animated explanation of Transcriptors, check out this series of graphics created by
Adam Cole for NPR.
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