Scientists have long wondered how life first began on Earth.
While we don’t have all the answers, one thing is clear: every living thing is made up of cells, and what separates a living cell from a random chemical reaction is a membrane.
These thin, protective barriers surround cells and control what comes in and out—an ability that may have helped shape the very chemistry of life.
A new study published in PLOS Biology explores how early cell membranes could have influenced the kinds of molecules that made it into cells and, eventually, became part of life as we know it.
The researchers focused on a curious feature shared by many biological molecules: chirality.
Chirality is a property that describes how some molecules twist or “turn” in space, like a left hand and a right hand. These mirror images are not interchangeable, even though they’re made of the same parts.
In living things, this matters a lot. For example, DNA and RNA—the molecules that carry genetic information—are made of sugars that all twist the same way (right-handed). Proteins, which do most of the work in cells, are built from amino acids that twist the opposite way (left-handed). Why life picked one “hand” over the other has puzzled scientists for decades.
To dig into this mystery, researchers studied how different types of membranes let molecules through. They looked at membranes similar to those found in archaea, a group of ancient microbes, and also tested a custom-designed membrane that mixed features from both archaea and bacteria.
They examined how easily different versions of sugars and amino acids could pass through these membranes.
Their results showed that right-handed sugars—those needed for DNA and RNA—could pass through the membranes more easily than their left-handed counterparts. This suggests early membranes may have favored the right-handed version, helping set the stage for life’s genetic code.
The results for amino acids were more mixed, but the team found that some left-handed amino acids, such as alanine (thought to be one of the first amino acids used by life), also passed through more easily, especially in the mixed-type membrane.
While these early membranes were only lab-made models, they offer a possible explanation for one of life’s biggest mysteries: how the specific twists of DNA, RNA, and proteins came to be so consistent across all living things.
As the researchers note, the membranes that formed around the first cells may have acted like sieves, naturally selecting the molecular “hands” that could pass through—and eventually, become life.
