Even as you read
this article, computer chip manufacturers are furiously racing
to make the next microprocessor
that will topple speed records. Sooner or later, though, this
competition is bound to hit a wall. Microprocessors made of
silicon will eventually reach their limits of speed and
miniaturization. Chip makers need a new material to produce
faster computing speeds.
You won't believe where scientists have found the new
material they need to build the next generation of
microprocessors. Millions of natural supercomputers exist
inside living organisms, including your
body. DNA (deoxyribonucleic acid) molecules, the material
our genes
are made of, have the potential to perform calculations many
times faster than the world's most powerful human-built
computers. DNA might one day be integrated into a computer
chip to create a so-called biochip that will push computers
even faster. DNA molecules have already been harnessed to
perform complex mathematical problems.
While still in their infancy, DNA computers will be
capable of storing billions of times more data than your
personal computer. In this edition of How
Stuff Will Work, you'll learn how scientists are using
genetic material to create nano-computers that might take the
place of silicon-based computers in the next decade.
A Fledgling Technology
DNA computers can't
be found at your local electronics store yet. The technology
is still in development, and didn't even exist as a concept a
decade ago. In 1994, Leonard Adleman introduced the idea of
using DNA to solve complex mathematical problems. Adleman, a
computer scientist at the University
of Southern California, came to the conclusion that DNA
had computational potential after reading the book "Molecular
Biology of the Gene," written by James Watson, who
co-discovered the structure of DNA in 1953. In fact, DNA is
very similar to a computer hard
drive in how it stores permanent information about your
genes.
Adleman is often called the inventor of DNA computers. His
article in a 1994 issue of the journal Science
outlined how to use DNA to solve a well-known mathematical
problem, called the directed Hamilton Path problem,
also known as the "traveling salesman" problem. The goal of
the problem is to find the shortest route between a number of
cities, going through each city only once. As you add more
cities to the problem, the problem becomes more difficult.
Adleman chose to find the shortest route between seven cities.
You could probably draw this problem out on paper and come
to a solution faster than Adleman did using his DNA test-tube
computer. Here are the steps taken in the Adleman DNA computer
experiment:
- Strands of DNA represent the seven cities. In genes,
genetic coding is represented by the letters A, T, C and G.
Some sequence of these four letters represented each city
and possible flight path.
- These molecules are then mixed in a test tube, with some
of these DNA strands sticking together. A chain of these
strands represents a possible answer.
- Within a few seconds, all of the possible combinations
of DNA strands, which represent answers, are created in the
test tube.
- Adleman eliminates the wrong molecules through chemical
reactions, which leaves behind only the flight paths that
connect all seven cities.
The success of the Adleman
DNA computer proves that DNA can be used to calculate complex
mathematical problems. However, this early DNA computer is far
from challenging silicon-based computers in terms of
speed. The Adleman DNA computer created a group of
possible answers very quickly, but it took days for Adleman to
narrow down the possibilities. Another drawback of his DNA
computer is that it requires human assistance. The goal
of the DNA computing field is to create a device that can work
independent of human involvement.
Three years after Adleman's experiment, researchers at the
University
of Rochester developed logic
gates made of DNA. Logic gates are a vital part of how
your computer carries out functions that you command it to do.
These gates convert binary code moving through the computer
into a series of signals that the computer uses to perform
operations. Currently, logic gates interpret input signals
from silicon
transistors, and convert those signals into an output
signal that allows the computer to perform complex functions.
The Rochester team's DNA logic gates are the first step
toward creating a computer that has a structure similar to
that of an electronic PC. Instead of
using electrical signals to perform logical operations, these
DNA logic gates rely on DNA code. They detect fragments of
genetic material as input, splice together these
fragments and form a single output. For instance, a genetic
gate called the "And gate" links two DNA inputs by
chemically binding them so they're locked in an end-to-end
structure, similar to the way two Legos might be fastened by a
third Lego between them. The researchers believe that these
logic gates might be combined with DNA microchips to create a
breakthrough in DNA computing.
DNA computer components -- logic gates and
biochips -- will take years to develop into a
practical, workable DNA computer. If such a computer is ever
built, scientists say that it will be more compact, accurate
and efficient than conventional computers. In the next
section, we'll look at how DNA computers could surpass their
silicon-based predecessors, and what tasks these computers
would perform.
A Successor to Silicon
Silicon
microprocessors have been the heart of the computing world for
more than 40 years. In that time, manufacturers have crammed
more and more electronic devices onto their microprocessors.
In accordance with Moore's Law, the number of
electronic devices put on a microprocessor has doubled every
18 months. Moore's Law is named after Intel founder Gordon
Moore, who predicted in 1965 that microprocessors would double
in complexity every two years. Many have predicted that
Moore's Law will soon reach its end, because of the physical
speed and miniaturization limitations of silicon
microprocessors.
DNA computers have the potential to take computing to new
levels, picking up where Moore's Law leaves off. There are
several advantages to using DNA instead of silicon:
- As long as there are cellular organisms, there will
always be a supply of DNA.
- The large supply of DNA makes it a cheap
resource.
- Unlike the toxic materials used to make traditional
microprocessors, DNA biochips can be made cleanly.
- DNA computers are many times smaller than today's
computers.
DNA's key advantage is that it will make
computers smaller than any computer that has come before them,
while at the same time holding more data. One pound of DNA has
the capacity to store more information than all the electronic
computers ever built; and the computing power of a
teardrop-sized DNA computer, using the DNA logic gates, will
be more powerful than the world's most powerful supercomputer.
More than 10 trillion DNA molecules can fit into an area no
larger than 1 cubic centimeter (0.06 cubic inches). With this
small amount of DNA, a computer would be able to hold 10 terabytes of
data, and perform 10 trillion calculations at a time. By
adding more DNA, more calculations could be performed.
Unlike conventional computers, DNA computers perform
calculations parallel to other calculations.
Conventional computers operate linearly, taking on tasks one
at a time. It is parallel computing that allows DNA to solve
complex mathematical problems in hours, whereas it might take
electrical computers hundreds of years to complete them.
The first DNA computers are unlikely to feature word
processing, e-mailing
and solitaire programs. Instead, their powerful computing
power will be used by national governments for cracking secret
codes, or by airlines
wanting to map more efficient routes. Studying DNA computers
may also lead us to a better understanding of a more complex
computer -- the human brain.
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