for National Geographic News
Israeli scientists have devised a computer that can perform 330
trillion operations per second, more than 100,000 times the speed of
the fastest PC. The secret: It runs on DNA.
in Rehovot, Israel, unveiled a programmable molecular computing machine
composed of enzymes and DNA molecules instead of silicon microchips.
Now the team has gone one step further. In the new device, the single
DNA molecule that provides the computer with the input data also
provides all the necessary fuel.
The design is considered a giant step in DNA computing. The Guinness
World Records last week recognized the computer as "the smallest
biological computing device" ever constructed. DNA computing is in its
infancy, and its implications are only beginning to be explored. But it
could transform the future of computers, especially in pharmaceutical
and biomedical applications.
Following Mother Nature's Lead
Biochemical "nanocomputers" already exist in nature; they are
manifest in all living things. But they're largely uncontrollable by
humans. We cannot, for example, program a tree to calculate the digits
of pi. The idea of using DNA to store and process information took off
in 1994 when a California scientist first used DNA in a test tube to
solve a simple mathematical problem.
Since then, several research groups have proposed designs for DNA
computers, but those attempts have relied on an energetic molecule
called ATP for fuel. "This re-designed device uses its DNA input as its
source of fuel," said Ehud Shapiro, who led the Israeli research team.
Think of DNA as software, and enzymes as hardware. Put them together in
a test tube. The way in which these molecules undergo chemical
reactions with each other allows simple operations to be performed as a
byproduct of the reactions. The scientists tell the devices what to do
by controlling the composition of the DNA software molecules. It's a
completely different approach to pushing electrons around a dry circuit
in a conventional computer.
To the naked eye, the DNA computer looks like clear water
solution in a test tube. There is no mechanical device. A trillion
bio-molecular devices could fit into a single drop of water. Instead of
showing up on a computer screen, results are analyzed using a technique
that allows scientists to see the length of the DNA output molecule.
"Once the input, software, and hardware molecules are mixed in
a solution it operates to completion without intervention," said David
Hawksett, the science judge at Guinness World Records. "If you want to
present the output to the naked eye, human manipulation is needed."
Don't Run to the PC Store Just Yet
As of now, the DNA computer can only perform rudimentary
functions, and it has no practical applications. "Our computer is
programmable, but it's not universal," said Shapiro. "There are
computing tasks it inherently can't do."
The device can check whether a list of zeros and ones has an even
number of ones. The computer cannot count how many ones are in a list,
since it has a finite memory and the number of ones might exceed its
memory size. Also, it can only answer yes or no to a question. It
can't, for example, correct a misspelled word.
In terms of speed and size, however, DNA computers
surpass conventional computers. While scientists say silicon chips
cannot be scaled down much further, the DNA molecule found in the
nucleus of all cells can hold more information in a cubic centimeter
than a trillion music CDs. A spoonful of Shapiro's "computer soup"
contains 15,000 trillion computers. And its energy-efficiency is more
than a million times that of a PC.
While a desktop PC is designed to perform one calculation very fast,
DNA strands produce billions of potential answers simultaneously. This
makes the DNA computer suitable for solving "fuzzy logic" problems that
have many possible solutions rather than the either/or logic of binary
computers. In the future, some speculate, there may be hybrid machines
that use traditional silicon for normal processing tasks but have DNA
co-processors that can take over specific tasks they would be more
suitable for.
Doctors in a Cell
Perhaps most importantly, DNA computing devices could revolutionize the
pharmaceutical and biomedical fields. Some scientists predict a future
where our bodies are patrolled by tiny DNA computers that monitor our
well-being and release the right drugs to repair damaged or unhealthy
tissue.
"Autonomous bio-molecular computers may be able to work as 'doctors in
a cell,' operating inside living cells and sensing anomalies in the
host," said Shapiro. "Consulting their programmed medical knowledge,
the computers could respond to anomalies by synthesizing and releasing
drugs."
DNA computing research is going so fast that its potential is
still emerging. "This is an area of research that leaves the science
fiction writers struggling to keep up," said Hawksett from the Guinness
World Records.
A summary of the research conducted by scientists at the
Weitzmann Institute of Science is published in today's online edition
of the Proceedings of the National Academy of Sciences.
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