Computing with DNA
DNA and molecular self-assembly may lead to smaller and more economical computers and photonic devices for future missions in space and on Earth.
Research Task: Biological Aspects of Computation (ITSR/RCA)
Principal Investigator: Leonard Adleman, Ph.D., University of Southern California
Is there a computer in your genes? An ITSR team led by Dr. Leonard Adleman has shown that DNA can be used to solve complex mathematical problems. In Adleman's lab at USC, one-fiftieth of a teaspoon of deoxyribonucleic acid (DNA) has solved two modestly difficult problems—the "Hamilton Path," or "Traveling Salesman," problem and the "Customer Satisfaction" or "NP-complete 3-SAT" problem. His experiment has been heralded as the "start of a new era," forging an unprecedented link between computational science and life science.
Unlike the zero-or-one, on-or-off, binary code of today's computer, the DNA code is based on four nucleotides—adenine (a), thymine (t), cytosine (c), and guanine (g)—that always pair the same way: a attaches to t, and c attaches to g. Adleman saw this predictable pattern as an opportunity to create a new kind of computer.
DNA computers are quick, performing 10^17 operations per second. They're efficient. With one joule of energy, which is what it takes a human to lift one kilogram one meter, a DNA computer can perform 2 x 10^19 (a million times a million times a million times 20) operations. They're capacious, too. A single gram of DNA can store the equivalent of one trillion CDs. Finally, they're economical. You can purchase a molecule of DNA for about one thousand trillionths of a cent. The amount of DNA used in Adleman's experimental "computer" cost about thirty dollars.
Obstacles, however, do stand in the way of using DNA to accomplish practical tasks. Adleman's current process requires creating, duplicating, and separating a number of DNA strands that increases exponentially with the number of variables. Some believe that the upper limit for mathematical computing is 70 to 80 variables. The process is also prone to error as the DNA strands exceed a certain length. Adleman is researching error-correction techniques.
Although DNA computers will not soon replace silicon-based computers, they may complement them. NASA would like to apply DNA computing to a computationally difficult NASA problem, such as event scheduling. Eventually, DNA computers may be used to control chemical/biological systems, as electronic computers control electrical/mechanical systems today.
NASA is also interested in self-assembly, the ability of simple forms to autonomously assemble into more complex forms. Nature provides many examples: atoms forming into molecules, molecules into crystals, and cells into organisms. Even heavenly bodies self-assemble into astronomical systems. Understanding this process, we might find a way to automatically fabricate computer circuits in great volume. Scientists have already used viruses to assemble nanocircuitry in a lab. Self-assembly could be useful in creating self-sufficient systems for deep space.
Dr. Adleman's team is exploring molecular self-assembly as a way to create nanoscale electronic and quantum devices. His team has already published algorithms for aiding self-assembly, and has successfully created and imaged 2-D structures. They are now working on 3-D shapes. Although still in its infancy, this technology could lead to smaller and more economical computers for future missions in space and on Earth. DNA computing and the process of self-assembly hold great promise, but even if they do not succeed, they may point the way to the real "computer of the future."
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