Biological NAND Gate: The future may be closer than we think

Digital circuits are built out of seven simple logic gates:  AND, OR, XOR, NOT, NAND, NOR, and XNOR.  These logic gates work by receiving a simple input and producing an output based on the input.  The AND gate will return a ‘True’ Boolean value if and only if both of its inputs are true, while the NOT gate will return a Boolean value of ‘True’ if the input is ‘False’, just like the words would suggest. Biologists at the Imperial College London have constructed an AND Gate and a NOT gate and were able to link them to produce a combitorial NAND Gate.  The NAND gate will return ‘True’ if both of the inputs are not ‘True’ (Figure 1).

Truth table of a NAND Gate. (http://whatis.techtarget.com/definition/0,,si_ gci213512,00.html)

The biological NAND gate (Figure 2) was constructed in E. coli.  The inputs are outputs are all natural biological molecules.  There are two inputs that go into the AND gate.  If both of the inputs are ‘True’, it will pass a ‘True’ value onto the NOT gate, which will then return a ‘False’.  If either of the inputs are ‘False’, the result of the NAND gate will be ‘True’.

Diagram of the synthetic NAND gate (Wang et al 2011).

Biological logic gates are not completely novel, but these new gates are able to be used in a number of biological systems and are modular, meaning that they can be joined together.  These improvements could lead to faster development of more complex biological circuits.  Once the seven simple logic gates are able to be constructed we will be able to make biological computing as complex as we would like.  Martin Buck, one of the authors on the paper, suggested that the gates could form the building blocks of microscopic biological devices.  His ideas include: sensors that can swim inside of arteries, search for harmful plaque, and deliver medications; sensors that could detect and destroy cancer cells inside the body; and sensors that could be deployed into the environment to detect and neutralize dangerous toxins (Quick, 2011).  They also propose that advanced circuits could be built to work as a projected image edge detector or a cellular event counter (Wang et al, 2011).  The possibilities are literally endless, and the future of medicine may be closer than we think.

Quick, D. (2011, October 21). Logic gates created from dna and bacteria could form basis of biological computers. Gizmag, Retrieved from http://www.gizmag.com/biological-logic-gates/20237/

Wang, B. et al. Engineering modular and orthogonal genetic logic gates for robust digital-like synthetic biology. Nat. Commun. 2:508 doi: 10.1038/ncomms1516 (2011).

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