| Nearly 75 years after its double-helix structure was first uncovered, DNA is a household name and a symbol for biology itself. But without its lesser-known cousin RNA, life wouldn't exist — a fact that's become only more apparent the more scientists study the single-stranded molecule that translates DNA instructions into cellular activity. In recent years, it's become clear that RNA's importance goes beyond that storied role. Biologists have revealed it to be the secret operator behind many functions in the cell, where it acts as an emergency alarm, a text messaging system, and so much more.
"I've been in awe of what RNA can do," Amy Buck, an RNA biologist at the University of Edinburgh, told Quanta last year. She's not the only one. As this xkcd comic portrays, some biologists now consider RNA an even more crucial cellular player than DNA.
In its classic role, mRNA (messenger RNA) is a copy-paste molecule: It copies sequences of DNA and ferries them out of the nucleus to the cytoplasm, where they can be used to make proteins. However, as sequencing and other technologies have improved, biologists have discovered other kinds of RNA molecules that are actors in their own right. For example, some microRNAs help regulate which proteins cells make, to guide the development of brain cells, for example. Circular RNAs help manage glucose metabolism. Transfer RNAs coat the surface of leaves and structure the plant microbiome. That's just the start of a long list of recent discoveries.
Such discoveries have led biologists to appreciate RNA's flexibility. They've started engineering the molecule for medicine, for example to create mRNA vaccines. These vaccines saved tens of millions of lives in their first year of use during the Covid-19 pandemic, though they are now under attack by the Trump administration. Some scientists are fascinated by the "RNA world" theory, which posits that life started with these simple genetic building blocks. If that theory is proved true, we will be able to say unequivocally: Yes, RNA is the star of the show called life.
What's New and Noteworthy A sunburn is our painful experience of what is fundamentally damage to cells. When ultraviolet light from the sun enters our skin cells, it can damage genetic material, and if the damage is not caught quickly it can kill the cell, cause harm to its neighbors or, in the worst-case scenario, develop into cancer. The body needs to identify genetic damage, and fast. Research published last year identified RNA as the center of a cell's emergency alert system. Ribosomes, the cellular machines that translate RNA into proteins, falter when reading UV-damaged RNA. They slow down, stop working and crash into each other — kicking off a signaling process that alerts the cell that something is wrong and needs to be taken care of. "Amazingly, it's the RNA that signals that. That's the remarkable observation," said study author and RNA biologist Rachel Green of Johns Hopkins University.
Because RNA is so ancient, it's a code that life across all the kingdoms can read and understand; thus, cells use RNA to communicate with each other, within and across species. By packaging little vesicles with short-lived strands of RNA, they send "text messages" to other cells. Biologists aren't quite sure how the recipient reads or uses these messages, but they have seen them used to build proteins in the recipient, which can help or harm the cell.
RNA might also be key to stabilizing some endosymbiotic relationships. One example is the partnership involving an alga called Chlorella that can often be found living inside an aquatic microbe called Paramecium bursaria. The pair trade food and nutrients, but the alga is in a vulnerable spot: Why doesn't the microbe just digest it? One study suggested that an "RNA brake" system might protect the alga (and the mutually beneficial partnership). If the Paramecium host attacked its algal endosymbiont, free-floating algal RNA would burst out into its cytoplasm, which could set off processes that would ultimately harm the larger microbe. Understanding this mechanism could be key to figuring out the story of how eukaryotes first evolved, likely from an ancient endosymbiotic relationship. | 
