Proceedings of the National Academy of Sciences
100.8 (April 15,2003): 4527–32, published online April 2,
2003, http://www.pnas.org/cgi/content/full/100/8/4527.
24.
Duke University press release, "Duke Scientists 'Program' DNA Molecules to Self Assemble into Patterned
Nanostructures," http://www.eurekalert.org/pub_releases/2003-09/du-ds092403.php,
referring to Hao Yan et
al., "DNA-Templated Self-Assembly of Protein Arrays and Highly Conductive Nanowires,"
Science
301.5641
(September 26, 2003): 1882–84. See also http://www.phy.duke.edu/~gleb/Pdf_FILES/DNA_science.pdf.
25.
Ibid.
26.
Here is an example of the procedure to solve what's called the traveling-salesperson problem. We try to find an
optimal route for a hypothetical traveler among multiple cities without having to visit a city more than once.
Only certain city pairs are connected by routes, so finding the right path is not straightforward.
To solve the traveling-salesperson problem, mathematician Leonard Adleman of
the University of
Southern California performed the following steps:
1.
Generate a small strand of DNA with a unique code for each city.
2.
Replicate each such strand (one for each city) trillions of times using PCR.
3.
Next, put the pools of DNA (one for each city) together in a test tube. This step uses DNA'saffinity to link
strands together. Longer strands will form automatically. Each such strand represents a possible route of
multiple cities. The small strands representing each city link up with each other in a random fashion, so there
is no mathematical certainty that a linked strand representing the correct answer (sequence of cities) will be
formed. However, the number of strands is so vast that it is virtually certain that at least one strand—and
probably millions—will be formed that represents the correct answer.
The next steps use specially designed enzymes to eliminate the trillions of strands
that represent wrong
answers, leaving only the strands representing the correct answer: 4. Use molecules called "primers" to destroy
those DNA strands that do not start with the start city, as well as those that do not end with the end city; then
replicate
the surviving strands, using PCR.
4.
Use an enzyme reaction to eliminate those DNA strands that represent a travel path greater than the total
number of cities.
5.
Use an enzyme reaction to destroy those strands that do not include city 1. Repeat for each of the cities.
6.
Now, each of the surviving strands represents the correct answer. Replicate these surviving strands (using
PCR) until there are billions of such strands.
7.
Using a technique called electrophoresis, read out the DNA sequence of these correct strands (as a group).
The readout looks like a set of distinct lines, which specifies the correct sequence of cities.
See L. M. Adleman, "Molecular Computation of Solutions
to Combinatorial Problems,"
Science
266
(1994): 1021–24.
27.
Charles Choi, "DNA Computer Sets Guinness Record," http://www.upi.com/view.cfm?StoryID=20030224-
045551-7398r. See also Y. Benenson et al., "DNA Molecule Provides a Computing Machine with Both Data
and Fuel,"
Do'stlaringiz bilan baham: