What is Biological computers?
INTRODUCTION Biological Computers
Biological
computers have emerged as an interdisciplinary field that draws together molecular
biology, chemistry, computer science and mathematics. The highly predictable hybridization
chemistry of DNA, the ability to completely control the length and content of
oligonucleotides, and the wealth of enzymes available for modification of the
DNA, make the use of nucleic acids an attractive candidate for all of these nanoscale
applications
A 'DNA computer' has been used for the first time to find the only correct answer
from over a million possible solutions to a computational problem. Leonard Adleman
of the University of Southern California in the US and colleagues used different
strands of DNA to represent the 20 variables in their problem, which could be
the most complex task ever solved without a conventional computer. The researchers
believe that the complexity of the structure of biological molecules could allow
DNA computers to outperform their electronic counterparts in future.
Scientists have previously used DNA computers to crack computational problems
with up to nine variables, which involves selecting the correct answer from 512
possible solutions. But now Adleman's team has shown that a similar technique
can solve a problem with 20 variables, which has 220 - or 1 048 576 - possible
solutions.
Adleman
and colleagues chose an 'exponential time' problem, in which each extra variable
doubles the amount of computation needed. This is known as an NP-complete problem,
and is notoriously difficult to solve for a large number of variables. Other NP-complete
problems include the 'travelling salesman' problem - in which a salesman has to
find the shortest route between a number of cities - and the calculation of interactions
between many atoms or molecules.
Adleman and co-workers expressed their problem
as a string of 24 'clauses', each of which specified a certain combination of
'true' and 'false' for three of the 20 variables. The team then assigned two short
strands of specially encoded DNA to all 20 variables, representing 'true' and
'false' for each one.
In
the experiment, each of the 24 clauses is represented by a gel-filled glass cell.
The strands of DNA corresponding to the variables - and their 'true' or 'false'
state - in each clause were then placed in the cells.
Each
of the possible 1,048,576 solutions were then represented by much longer strands
of specially encoded DNA, which Adleman's team added to the first cell. If a long
strand had a 'subsequence' that complemented all three short strands, it bound
to them. But otherwise it passed through the cell.
To move on to the second clause of the formula, a fresh set of long strands was
sent into the second cell, which trapped any long strand with a 'subsequence'
complementary to all three of its short strands. This process was repeated until
a complete set of long strands had been added to all 24 cells, corresponding to
the 24 clauses. The long strands captured in the cells were collected at the end
of the experiment, and these represented the solution to the problem.
THE
WORLD'S SMALLEST COMPUTER
The world's smallest computer (around a trillion can fit in a drop of water) might
one day go on record again as the tiniest medical kit. Made entirely of biological
molecules, this computer was successfully programmed to identify - in a test tube
- changes in the balance of molecules in the body that indicate the presence of
certain cancers, to diagnose the type of cancer, and to react by producing a drug
molecule to fight the cancer cells.
q Facial recognition is a form ofcomputer
vision that uses faces to attempt to identify a person or verify a person’s
claimed identity. Regardless of specific
method used. 
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