food for thought...from the Wired synthetic biology article...

genetic code contains only four letters: A, C, G, and T, which stand for the four nucleotide bases that make up DNA (adenine, cytosine, guanine, and thymine). Every possible three-letter DNA word - ACT, GCA, and so on - either denotes one of 20 amino acids used to make proteins or instructs a cell's protein-making machinery to stop making protein. A gene is a long string of such words that specify the order in which to assemble amino acids, resulting in a given protein.

Because there are 64 three-letter words in the DNA language and only 20 amino acids required by biology, there's more than one possible word for most of the acids. For example, the amino acid arginine has six DNA synonyms. This redundancy makes it possible to add new words to the genetic code.

Imagine typing all the three-letter words of a bacterial genome in a text editor and changing all uses of the four less common words for arginine to the two most common. This would preserve the meaning of every gene while giving you four spare words. Presumably you could reassign them to new amino acids - amino acids that living creatures have never used before. This may sound far out, but it has already been done. Scientists at the Scripps Research Institute in La Jolla, California, have modified a bacterium to read a word that normally means "stop making protein" as "add a weird amino acid here."

Extending the genetic code in this way opens a wide range of possibilities that are obvious to chemists but that nature has never tried, because it simply didn't have enough words to work with. You could enhance proteins with fluorescent amino acids, making them easier to track as they wander around cells. You could give proteins chemical hooks that would make it easier for them to link to certain sugars, which would be especially useful for proteins in drugs.

New proteins are just the beginning. Rejiggering the genetic code could also eliminate some worries about biotechnology. Synthetic creatures based on a code that looked like nonsense to natural systems couldn't exchange genes with familiar flora and fauna, and thus couldn't escape into the wild. More ambitiously, engineers could build life-forms out of entirely different building blocks. For example, some molecules come in two mirror-image forms, like a pair of hands. Nature uses left-handed amino acids and right-handed sugars. If synthetic organisms worked the other way around, they would be incapable of making use of natural foodstuffs, thus ruling out most of the ways they could disrupt natural ecosystems.