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Inside the "Synthetic Cell"

Scientists are a step closer to creating life from scratch, as J. Craig Venter and his colleagues announced yesterday that they have synthesized a complete bacterial genome and installed it in a "synthetic cell" capable of replicating itself.

So, what defines a cell as "synthetic?" Haven't scientists been tinkering with genes for a while now? What makes this new work so special? I checked in with the producer of NOVA scienceNOW's "Artificial Life" segment, Julia Cort, and biologist David Deamer, who is featured in that segment, to find out. Now, if you haven't watched the segment yet, I'll give you a sneak preview: You'll see a scientist programming a string of genetic code into a computer, while a machine stocked with little bottles of the chemicals adenine, cytosine, guanine, and thymine, pops out artificial DNA to order. This segment ran back in 2005, so cooking up DNA from scratch is not a new thing.

But the scientists you'll see in the segment weren't synthesizing full genomes. They were whipping up a gene for this and a gene for that, and slipping them in to the "natural" DNA that lives in cells. Venter and his colleagues, on the other hand, have synthesized the whole shebang, creating a machine-made near-carbon-copy of a bacterial genome and stationing it inside a cell that's been wiped clean if its own DNA. That's no small feat, Deamer explained. Typically, synthesized DNA can only hold about 300 chemical "letters" before mistakes start to pile up. Venter and his team scaled that up to a million letters.

How did they do it? They started out with short segments of lab-made DNA, then stitched them together to create a full DNA loop. Then, they transplanted that DNA into a waiting cell--and nothing happened. After three months of "debugging," the team spotted a single errant letter in their synthetic code. Once they fixed it, the cell "booted up" properly.

So, what didn't Venter's group do? They didn't make artificial life. As Deamer put it, their work is more like a tremendously expensive biological Xerox. The DNA Venter's team synthesized was cribbed from an existing bacterium, and the cell into which the DNA was transplanted was a "natural" cell. So if DNA is like a computer's operating system, Venter's team lifted a copy of Windows Vista from one computer, retyped all the code, and booted it up on a different machine.

So, what's next? How about making biofuels using genetically-engineered cells, suggests Deamer. But it took dozens of scientists and tens of millions of dollars to make this one synthetic genome, and we don't know yet whether full "prosthetic genomes" will turn out to be a commercially scalable technology. In any case, policymakers are waking up to a new slate of bioethical questions; President Obama has already asked the Commission for the Study of Bioethical Issues to take up a study of the ethical implications of the synthetic genome.
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