DNA has long been the scientific superstar; now RNA is stealing the spotlight. Before there were bacteria, before there were archaea or eukaryotes, there were ribocytes—primitive replicating microbes that did all their biochemical maneuvering with RNA alone. “Ribocytes were likely cells because the most plausible way to maintain a coherent evolutionary identity is to be membrane delimited,” according to Michael Yarus, of the University of Colorado at Boulder. The limit-defining outer membrane of these simple creatures was probably made of cosmochemicals—“that is, amphipathic lipids [that] occur naturally and broadly in the universe and don’t require complex biosynthesis,” he explains. Such amphipathic lipids— fatty biomolecules with both water-friendly and -phobic regions that enable them to form bilayers in cell membranes—are still common today in the form of phospholipids.
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