Every cell is made of three basic parts: genetic information in the form of DNA or RNA, proteins that provide function and structure, and a surrounding membrane to hold everything together. However, such fatty acid membranes destabilize both in saltwater, where life first arose, and in the presence of the magnesium ions required by RNA. So how did the first cells come to be? A new study suggests it takes one simple ingredient to stabilize the membranes, The Atlantic reports: amino acids. Scientists found that when they mixed these protein building blocks with fatty acids before adding salt or magnesium ions, not only did the membranes stay intact, they also formed double layers that more closely resemble the structure of modern cells, they reported Monday in the Proceedings of the National Academy of Sciences.