We're closer than ever to turning our bodies into computers. A study published this week in Science demonstrates how to turn DNA into a simple counter. That means your DNA could eventually be reprogrammed with a shut down command.
One of the many features of DNA is that it responds to signals over time. It interacts with molecules and enzymes in the cell which often tell it to do something later, after it has received several other chemical signals - or to react instantly when in the presence of certain proteins. The fact that DNA responds predictably to certain signals means that it could be turned into a counter that measures time via regularly delivered molecular signals. So if you built a biological machine that needed to count particulate matter in the air, DNA would be the perfect mechanism to use. Just a reengineer it to emit a particular protein after it had encountered, say, 10 particles of a toxin - then create a device that rings a bell when it sees the protein. Poof - you've got a biological machine that rings a bell when dangerous toxins are in the air.
Stanford synthetic biologist Christina D. Smolke described the importance of this new study in Science to us via e-mail:
A counter will allow you to program function or trigger responses based on frequencies of detected events over time (and therefore are an important component of programming in time and space). One of the more immediate applications would be trigger an event in response to a certain number of cell divisions or cell cycles. For instance, if there were a molecule associated with a certain phase of the cell cycle one could 'count' that molecule over time and therefore count the number of cell cycles. In this case, one might want to trigger cell death after a certain number of cell cycles as a means to avoid uncontrolled cell growth (or cancer)... You can also imagine wanting to detect not just the concentration of an environmental contaminant, but also its frequency of occurrence over time. Other technologies could use this as a safety kill switch, such that if one is releasing an engineered microorganism into the environment, you could use this counter to trigger its death after a certain number of cell divisions to provide better control over the engineered system and less chance for spreading from the intended application.
Most of the applications for this biotechnology are in medicine, but as Smolke points out you really could build a toxin sensor, or even a cell that is programmed to die after a set amount of time.
You can read Smolke's entire article in Science, and you can read the study she described in the same issue.