The discovery of the language of life, an ancient, long molecule called DNA with eight nucleotide letters suitable for storing and transmitting information, was a breakthrough in our knowledge of the range of possibilities necessary for life on Earth and beyond. Now, new studies suggest that alternatives to DNA-based life, as we know it on Earth, may be possible on other worlds.
DNA –a giant among molecules
DNA, a giant among molecules, was discovered in 1869 by the Swiss chemist Friedrich Miescher. Every cell in your body contains about two meters of it. Etched into its famous double-helix structure is the instruction manual for life. The basic recipe is the same for all known life: we share about 7% of our genes with Neanderthals, 98 per cent with chimpanzees, 85 per cent with mice, 60 per cent with chickens and more than half with many bacteria.
“A molecule with crystalline levels of stability that could be arbitrarily structured might encode and store a vast amount of information, which is precisely what DNA turned out to be: an aperiodic crystal,” writes astrophysicist Paul Davies in The Demon in the Machine (p. 25 University of Chicago Press. Kindle Edition)
In a research breakthrough funded by NASA announced on February 21, 2019, scientists synthesized a molecular system that, like DNA, can store and transmit information. This unprecedented feat suggests there could be an alternative to DNA-based life, as we know it on Earth – a genetic system for life that may be possible on other worlds.
This new molecular system, which is not a new life form, suggests scientists looking for life beyond Earth may need to rethink what they are looking for. .
DNA is a complex molecule that stores and transmits genetic information, is passed from parent to offspring in all living organisms on Earth, and its components include four key ingredients called nucleotides – all standard for life as we know it. But, what about life on other worlds?
“Life detection is an increasingly important goal of NASA’s planetary science missions, and this new work will help us to develop effective instruments and experiments that will expand the scope of what we look for,” said Lori Glaze, director of NASA’s Planetary Science Division.
The illustration above shows the structure of a new synthetic DNA molecule, dubbed hachimoji DNA, which uses the four informational ingredients of regular DNA (green, red, blue, yellow) in addition to four new ones (cyan, pink, purple, orange). (Indiana University School of Medicine)
Now, scientists computed a zoo of millions of alternate genetic polymer molecular structures, giving context for why biology encodes information how it does, and providing a guide to searches for extraterrestrial biology. A new study released by the Tokyo Institute of Technology suggests that more than 1 million chemical look-alikes could encode biological information in the same way that DNA does. The new study, published Sept. 9 in the Journal of Chemical Information and Modeling, might explain how life first evolved on Earth and even help us search for life-forms beyond our planet, the authors wrote.
“It is truly exciting to consider the potential for alternate genetic systems … that these might possibly have emerged and evolved in different environments, perhaps even on other planets or moons within our solar system,” co-author Jay Goodwin, a chemist at Emory University, said in a statement.
Both DNA and RNA, the two known types of nucleic acids, contain chemical bits called nucleotides, which link up in a particular order and relay different data, depending on their sequence, similar to individual letters within a written sentence. Some natural and man-made molecules mimic the basic structure of DNA, but before now, no one had attempted to count up how many of these look-alikes might exist, the authors wrote.
“There are two kinds of nucleic acids in biology,” co-author Jim Cleaves, a chemist at the Tokyo Institute of Technology, said in the statement. “We wanted to know if there is one more to be found or even a million more. The answer is, there seem to be many, many more than was expected,” Cleaves said.
The authors designed a computer program to generate chemical formulas for nucleic acid-like molecules. In DNA, nucleotides couple up in distinct pairings and assemble in a line, so the scientists made sure that their generated molecules could form in the same way. In the end, their program put together more than 1,160,000 different molecules that met these basic criteria.
The mind-boggling number of nucleic-acid-like molecules suggest that evolution may have performed “test runs” with some of these other molecules before settling on nucleic acids as the best conveyors of genetic data, the authors wrote.
Image credit: Scientists have found there are likely millions of ways of storing biological information. But why does biology do it the way it does? Used under CC0 1.0 license