How far off are scientists from making a synthetic cell?
So far in synthetic biology, manipulations have been limited to designing different genetic circuits by reshuffling some of the natural genes to perform a particular task and moving metabolic pathways from one organism into another. For example, the Keasling group engineered a metabolic pathway in Escherichia coli that produces precursors to the antimalaria drug artemisinin. Currently, the drug is harvested from the Artemisia annua plant, but it is very expensive to produce. However, these researchers also reproduced this plant metabolic pathway in yeast, allowing for an inexpensive way to produce the drug. Furthermore, the Voigt group engineered E. coli to produce spider silk, one of the strongest fibers known. Another area where there is progress in synthetic biology is designing almost digital-like circuits by perturbing gene control at different levels (transcriptional, translational, posttranslational). For example, scientists can currently design circuits that perform Boolean logic (i.e., involving AND, OR, and NOT operations). In this way, biological organisms can act as sensors, for example, producing an output only when they sense "A" AND they sense "B." In an effort to push the field further, several organizations are trying to make parts of genetic circuits more modular, so that one could just pick the desired parts and combine them like interlocking bricks to have a desired logic/output performed (e.g., see http://biobricks.org/).
However, many challenges still exist. Compared to electronics, biological systems have a lot of noise; rather than predictably producing an exact output, they generate drastically variable results. A lot of “bricks” are not well-defined; therefore, they work either only in a particular organism or only under particular conditions. The circuits are not as predictable as one would think, because of unknown interactions with the host organism machinery. Finally, way too much is still not known about natural biological processes and circuits, leading to more of a “black box testing” scenario, rather than purposeful design. However, because the price of DNA synthesis and sequencing has dropped over the past few years, allowing more and more scientists to tinker with genetic circuits, it is only a matter of time before a very simple synthetic cell is designed.