Unnatural DNA used to encode unnatural proteins, all in otherwise normal cells.
To the best of our ability to tell, everything on Earth shares a few common features. It encodes information in DNA using four bases, A, T, C, and G. Sets of three consecutive bases are used to code for a single amino acid, and most organisms use a set of 20 amino acids to build proteins. These features appear everywhere, from plants and animals to bacteria and viruses, suggesting that they appeared in the last common ancestor of life on Earth.
This raises a question that comes up a lot in evolutionary studies: are these features used because they’re in some way efficient, or did we end up stuck with them as a result of some historic accident?
Source: Life, but not as we know it