Could we rewrite the instructions for life?

Every living thing on earth is made from a genetic sequence that contains four different nitrogenous bases – adenine (A), guanine (G), cytosine (C) and thymine (T). You can think of these bases like letters in a language – different words arise depending on the way they are arranged. However, unlike the 26 letters we have in the English language, nature only has four. But marvelously, these four letters are used to write genetic codes for over a million different types of living species. It stands to reason then that these four letters are special; they’re selected, optimized, and entrusted by nature to hold the instructions for life.

But what if we could rewrite those instructions? A group of scientists were recently able to make a DNA sequence with four new, completely synthetic, nucleobases. This eight-letter genetic code combined the standard A, G, C, and T, with new letters Z, P, S, and B. Normal DNA sequences fold into the shape of a long, spirally structure called a double helix. This shape is crucial for the long-term storage of genetic information and is therefore necessary for preserving the fidelity of life. These scientists showed that different 8-letter DNA sequences were all able to maintain a double helical structure and also exhibit chemical and physical properties similar to normal DNA. To further demonstrate the legitimacy of these new letters, they also showed that their synthetic sequence could be used to make RNA, the functional genetic instructions that are “read” by cellular machinery to make living things.  

The successful advent of 8-letter DNA expands our ability to store information – with 8 letters, we could write the same instructions in significantly less space, improving the potential for DNA to be used as a hard drive of sorts. Additionally, synthetic DNA could have medical and biotechnological implications. Short sequences of DNA are sometimes used to locate specific molecules, such as those that are uniquely expressed in cancer cells. More base options allow for more specificity, improving the targeting properties of these DNA sequences.

Most profoundly however, synthetic DNA also suggests that our DNA isn’t particularly special. There isn’t something uniquely perfect about the four bases nature chose for life on earth – in fact, life on other planets could exist with completely different types of genetic information, and a DNA scan may be insufficient to survey for life. Even if we don’t find extraterrestrial life forms, research in this field could be en route to engineering its own synthetic organisms – which would maybe be too close to all those famous sci-fi dystopian movies for comfort.

Peer edited by Nicole Fleming.

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